Bulletin of the British Museum (Natural History). British Museum (Natural History) Converted as part of the ABLE project by Dauvit King London : BM(NH) Set of bird parts only held at TOS 112. General Library missing Vol 55-56, 1989-90 Vol.1 (1950)- 4 5 6 This document has been converted to TEI XML as part of the ABLE project to make it more widely available to biodiversity researchers in a useful format. eng text No corrections have been made in the text. The original source has not been regularized or normalized. Quotation marks have not been processed. They are as in the original DjVu XML document. Hyphens, including end-of-line hyphens, have not been processed. They are as in the original DjVu XML document. The text has been segmented based purely on layout based on page breaks. No language level segmetation, such as sentences, tone-units or graphemic, has been applied. Additional mark up using taXMLit has been applied to the TEI XML based on analysis of the original source through the uBio and OpenCalais web services. (Add comment for fuzzy matching once this has been brought into the final workflow too.) Bulletin of the British Museum (Natural Histd GvHWM Zoology series Vol 36 1979 British Museum (Natural History)London 1980 Dates of publication of the parts No 1 28 June 1979 No 2 26 My 1979 No 3 27 September 1979 No 4 25 October 1979 No 5 29 November 1979 ISSN 0007-1498 Printed in Great Britain by Henry Ling Ltd, at the Dorset Press, Dorchester, Dorset ContentsZoology Volume 36 f v No 1 A guide to the species of the genus Aspidisca I. C. H. Wu & C. R. Curds No 2 The Hemiuroidea : terminology, systematics and evolutionD. I. Gibson & R. A. Bray No 5 Anatomy, relationships and classification of the families Citharinidaeand Distichodontidae (Pisces, Characoidea)R. P. Vari . 35 No 3 Notes on the anatomy of Macrochirichthys macrochirus (Valenciennes),1844, with comments on the Cultrinae (Pisces, Cyprinidae)G. J. Howes 147 No 4 Miscellanea Siliceous structures secreted by members of the subclass Lobosia(Rhizopodea : Protozoa) C. G. Ogden The first recorded specimens of the deep-water coral Lophelia pertusa(Linnaeus, 1758) from British Waters J. B. Wilson The larval and post larval development of the brachyuran crab Geryontridens Kroyer (Family Geryonidae) reared in the laboratory R. W. Ingle Notes on the types of scorpions in the British Museum (NaturalHistory), London. Buthus socotrensis Pocock, 1889 (Family : Buthidae) M. Vachon Five new prawn-associated gobies (Teleostei : Gobiidae) of the genusAmblyeleotris N. V. C. Polunin & R. Lubbock The taxonomy of Procavia capensis in Ethiopia, with special referenceto the aberrant tusks of P. c. capillosa Brauer (Mammalia, Hyracoidea)G. B. Corbet 203 209 217 233 239 251 261 Bulletin of the British Museum (Natural History) Irene C. H. Wu & Colin R. Curds Zoology series Vol 36 No 1 28 June 1979 The Bulletin of the British Museum (Natural History), instituted in 1949, is issued in fourscientific series, Botany, Entomology, Geology (incorporating Mineralogy) and Zoology,and an Historical series. Papers in the Bulletin are primarily the results of research carried out on the unique andever-growing collections of the Museum, both by the scientific staff of the Museum and byspecialists from elsewhere who make use of the Museum's resources. Many of the papers areworks of reference that will remain indispensable for years to come. Parts are published at irregular intervals as they become ready, each is complete in itself,available separately, and individually priced. Volumes contain about 300 pages and are notnecessarily completed within one calendar year. Subscriptions may be placed for one or moreseries. Subscriptions vary according to the contents of the Volume and are based on a forecastlist of titles. As each Volume nears completion, subscribers are informed of the cost of thenext Volume and invited to renew their subscriptions. Orders and enquiries should be sent to: Publication Sales, British Museum (Natural History),Cromwell Road, London SW7 5BD,England. World List abbreviation: Bull. Br. nat. Hist. (Zool.) Trustees of the British Museum (Natural History), 1979 ISSN 0007-1498 Zoology series Vol 36 No 1 pp 1-34 British Museum (Natural History) Cromwell Road London SW7 5BD Issued 28 June 1979 A guide to the species of the genus Aspidisca Irene C. H. Wu & Colin R. Curds Department of Zoology, British Museum (Natural History), Cromwell Road, London SW7 5BD Introduction As a sequel to 'A guide to the species of the genus Euplotes"" (Curds, 1975) the present paper isprimarily a collection of diagrams and descriptions of the species of the genus AspidiscaEhrenberg, 1830 (1832). Keys to what we consider to be distinct species are included, and aredesigned to enable workers to make specific identifications of Aspidisca without the need tosearch the literature. Previous attempts known to the present authors are those of Plough (1916)who devised a key to eight species (see Appendix 1) and Kahl (1932) whose key included 28species (see Appendix 2). Borror (1972), in a revision of the order Hypotrichida Stein, 1859,listed 22 species of Aspidisca with their synonyms. While we sometimes do not agree with Borror(1972), it should be pointed out that some of the disagreements are only matters of opinion.Information is still required to substantiate these opinions even though some effort has recently(Tuffrau, 1964; Borror, 1972; Curds, 1975, 1977) been devoted to the taxonomy of the familyEuplotidae Ehrenberg, 1838. Since Ehrenberg, 1830 (1832) established the genus Aspidisca withAspidisca lynceus (Miiller, 1773) Ehrenberg, 1830 as the type species, over 50 nominal specieshave been transferred and added to the genus. Species have been distinguished by the size andshape of the body, the number of dorsal ribs, the presence of a thorn on the dorsal surface, thenumber of cirri on the ventral surface, nuclear features and the configuration of the peristome.Kahl (1932) applied all these criteria in devising his key (Appendix 2) and divided them intomarine and freshwater species. Plough (1916), on the other hand, considered the shape of the'cuirass' to be the most stable character and believed that the numbers and disposition of cirrito be variable. More recently, silver-impregnation techniques have been used to study themorphology and morphogenesis of ciliates. The diagnostic value of the silver-line systems ofAspidisca spp. and the other features mentioned above will be discussed under separate headings. Features of taxonomic importance (a) Habitat The freshwater species listed by Kahl (1932) include A. lynceus, A. costata, A. turrita, A. herbicola,A. marsupialis and A. sulcata. Earlier Plough (1916) had reported the occurrence of A. turrita andA. costata in both sea water and freshwater but stated the others, including A. lynceus, to bestrictly marine species. In fact the original specimens of A. lynceus were found in freshwater andthe species has since been reported in freshwater sites (Kahl, 1932; Bick, 1972). A. herbicolaKahl, 1932 appears to be the only species which is reported to occur in freshwater alone. Allother species described to date inhabit the marine environment. (b) Size It is known that the size of a ciliate may vary with many factors including rate of growth, con-centration of food, kind of food and so on, and is therefore of limited taxonomic value (see Curds,1975). In the case of Aspidisca, while their sizes range from 16 to 150 um long most species arebetween 50 and 100 urn long (Fig. 1). Therefore, the exceptionally large size (135-150 um) ofA. magna Kahl, 1932 can perhaps justifiably be regarded as diagnostic. (c) Shape The typical shape of Aspidisca is oval although it generally tends to be more convex on theright than on the left. The outline may be smooth or jagged with spurs or dentations whichmostly appear on the left border. The dorsal surface is commonly arched and it may be smooth Bull. Br. Mus. not. Hist. (Zool.) 36 (1): 1-34. Issued 28 June 1979 I. C. H. WU & C. R. CURDS Fig. 1 Sizes of some Aspidisca species: (a) A. polys tyla; (b) A. magna; (c) A. lyncaster (calledA. leptaspis in this revision); (d) A. pulcherrima; (e) A. magna (after Tuffrau, 1964). or longitudinally marked by indistinct furrows, conspicuous ribs and sometimes a posteriorlydirected curving thorn. Plough (1916) distinguished species primarily by the number of spurs on the left border andindeed, by the relatively crude earlier diagrams, the number of spurs does appear to be the mostdistinctive feature among the species Plough included (Fig. 2). More specimens with serratedborders have since been studied in greater detail. In many cases the actual number of spurspresent and the degree to which they are developed is variable and there is considerable differencebetween descriptions (Fig. 3). However, a projection from the peristomial area on the left borderis found on all species with serrated borders. Thus we do not intend to separate species by thenumber of peripheral serrations but consider the presence of a 'peristomial spur' diagnostic. a "A^V b V C Fig. 2 Ventral surfaces of : (a) Aspidisca hexeris (called A. sedigita in this revision); (b) A. lyncaster; (c) A. sedigita (after Plough, 1916). THE GENUS ASPIDISCA a be Fig. 3 Ventral surface of Aspidisca lyncaster (called A. leptaspis in this revision): (a) after Tuffrau,1964; (b) after Kahl, 1932; (c) after Dragesco, 1960. (d) Dorsal ribs and thorn Many workers have reported that the dorsal ribs and thorn noted in several species of Aspidiscaare inconsistent in size, number and even their presence. Diller (1975) stated that his specimensof A. costata usually had six to seven dorsal ribs but the number varied considerably within thethree to ten range. Hamm (1964) showed that the size of the dorsal ribs of A. costata vary underdifferent growth conditions (Fig. 4). The dorsal thorn of A. turrita has also been found to varyin size (Ehrenberg 1838; Claparede & Lachmann 1858). Kahl (1932) stated that this thorn issometimes missing while Borror (1965) mentioned that a dorsal thorn was present on only someof his specimens of A. aculeata (Ehrenberg, 1838) Kahl, 1932. However, in both cases there areinsufficient data to be certain that the specimens with and without a dorsal thorn are the samespecies. In the following keys, the actual presence of ribs, crenated ribs or thorn on the dorsalsurface will be used as diagnostic characters but their number and size will be regarded astaxonomically insignificant. More conclusive studies of clonal cultures of Aspidisca with dorsalribs, thorn and peripheral projections would be most valuable, particularly so as variable dorsalridges and lateral projections have been recently noted (Curds, 1977) in a related hypotrich,Euplotes aediculatus. (e) The adoral zone of membranelles The genus Aspidisca is characterised by a two-part adoral zone of membranelles (AZM) alongthe left border. The posterior part is a series of 8-20 membranelles lining the peristome which ispartially enclosed by the ventral plate and the anterior part is a group of cilia-like structures,two to eight in number, often confined in an indentation of the ventral plate. Kahl (1932) andDragesco (1965) regarded the configuration of the flap of ventral plate over the buccal cavity as a D c Fig. 4 Aspidisca costata showing dorsal ribs of: (a) normal type; (b) overfed form; (c) starvedspecimen; (d) specimen with extremely high ribs; (e) specimen from an adverse environment(called A. cicada in this revision after Hamm, 1964). 4 I. C. H. WU & C. R. CURDS a specific character but we find it not sufficiently distinctive to be of significant taxonomic value.The peristome is generally triangular, about one third to half of the body size in length and onefourth to one third in width. In some cases, the peristome extends forward and almost meets theanterior group of ciliary structures which is referred to by different names in the literature andis often regarded as a specialised section of the AZM. We refer to this group of 'cilia' as theanterior ciliary organelle. Diller (1975), who called the organelle a 'tooth', stated that thedifferentiation of this and the AZM are independent in A. costata and suggested that it is equiva-lent to the I/I cirrus in Euplotes (using the system of Wallengren 1900); this suggestion does not a < i o Fig. 5 Some stages of nuclear reorganisation in Aspidisca lynceus: (a) the macronucleus of a normalresting individual ; (b) an early stage in the formation of the reorganisation band ; (c) reorganisationbands completely separated by the central chromatin; (d) nucleus about one-half reorganised;(e) reorganisation about two-thirds complete; (f) the beginning of condensation. Micronucleusin prophase; (g) bands about to disappear; (h) macronucleus fully condensed; (i) constriction ofthe macronucleus; (j) daughter macronucleus slightly after division; (k) macronucleus of a youngdaughter individual (after Summers, 1935). conform with the scheme for Aspidisca presented by Tuffrau (1964) (see Fig. 1 1). The numbers ofmembranelles in the posterior AZM and of the 'cilia' in the anterior ciliary organelle will bementioned, if known, in the following descriptions even though they seem to have little diagnosticvalue. (f ) Nuclear features It has long been recognised that the nuclei of ciliates are of taxonomic importance. Themacronucleus of hypotrichs such as Euplotes takes a variety of forms during reorganisation;however, during 'interphase' it is constant and characteristic of the species (see Curds, 1975).Most Aspidisca spp. have, like Euplotes, a C-shaped or horseshoe-shaped macronucleus and aspherical micronucleus and Summers (1935) described the division and reorganisation of themacronucleus of A. lynceus to be comparable to that of Euplotes. A band-like macronucleushas been described by Ghosh (1921) and several authors have illustrated horseshoe-shapedmacronuclei with dilated centres. These may correspond to two of the divisional stages of themacronucleus of A. lynceus as illustrated by Summers (Fig. 5). A small number of species havebeen found to have two oval or ellipsoid macronuclei. While Tuffrau (1964) suggested that thepresence of two macronuclei in A. major (Madsen, 1931) Kahl, 1932 might represent a transi-tional stage, this has not been confirmed and the presence of two macronuclei is used as adiagnostic character in the following keys. Summers (1935) stated that one micronucleus waspresent in trophic A. lynceus, but Borror (1965) found there were one to three micronuclei in his THE GENUS ASPIDISCA Fig. 6 Dorsal silver-line systems of: (a) Aspidisca cicada (after Curds, 1977); (b) Aspidisca lynceus(after Klein, 1929); (c) Euplotes sp., single-vannus type after Curds, 1975; (d) Euplotes sp., double-patella type after Curds, 1975. specimens of A. aculeata. Agamaliev (1967, 1971) observed similar variation in A. caspicaAgamaliev, 1967 while Dragesco (1954) described A. hyalina as possessing four micronuclei.Summers (1935) noted that although the division of the micronucleus is usually initiated when thereorganisation process of the macronucleus is about two thirds complete, it may be much earlier.Dini & Bracchi (1976) who studied the nuclear cycle of A. aculeata also found that division of themicronucleus preceded that of the macronucleus. Therefore the presence of two micronuclei maybe a transitional state. On the other hand, Dini & Bracchi stated that 'when more micronucleiare present in the same cell, they divide asynchronously'. These data suggest that the number ofmicronuclei should not be used as a taxonomic criterion until the micronuclear activities ofAspidisca are better understood. (g) Dorsal argyrome It was hoped that the patterns of the dorsal argyrome or silver-line system of Aspidisca wouldbe valuable for specific identification. Unfortunately, only a few workers have described thedorsal silver-line system of the species studied and some have encountered technical difficultiesin applying the silver-impregnation methods to this genus although the ventral argyrome and I. C. H. WU & C. R. CURDS a b Fig. 7 Dorsal silver-line system of: (a) Aspidisca aculeata; (b) Aspidisca leptaspis (after Agamaliev, 1974). cirral bases are usually successfully stained. Even Tuffrau (1964), who pioneered the applicationof the argyrome patterns for the diagnosis of Euplotes, only gave incomplete descriptions of thesilver-line systems of Aspidisca spp. which he studied. Klein (1929) and Curds (1977) used thedry silver method (see Klein, 1958) to stain A. lynceus and A. cicada respectively. They foundthat both of these species have distinctly different argyrome patterns from those described in thegenus Euplotes (Fig. 6). In neither case did the staining depict any connections between thekinetics. However, A. aculeata and A. leptaspis Fresenius, 1865 have dorsal argyromes similar tothose of Euplotes with four dorsal kinetics connected by single links (Fig. 7). Furthermore, thesilver-line systems of A. polystyla Stein, 1859 and A. major (Madsen, 1931) Kahl, 1932 weredescribed by Tuffrau (1964) as having four kinetics with argyrome patterns like those of Euploteseurystomus. Agamaliev (1967, 1971) studied the silver-line system of A. caspica and found thedorsal argyrome pattern to be highly variable. He observed single, double and multiple rows ofpolygons between the kinetics in this species and that the number of dorsal cilia was also highlyvariable (Fig. 8). Recently Gates & Curds (1979) noted that the geometry of the dorsal argyromein different stocks of the same clone of Euplotes varies significantly. Because of the paucity of a b c Fig. 8 Dorsal silver-line patterns of Aspidisca caspica: (a) after Agamaliev, 1967;(b & c) after Agamaliev, 1971. THE GENUS ASPIDISCA 7 data concerning the dorsal argyrome and its reported variability, we have not used it for specificidentification but do add information on it when available. (h) The cirri We believe that the numbers and arrangements of the cirri on the ventral surface of Aspidiscaare the most stable diagnostic features. With few exceptions, Aspidisca spp. have seven fronto-ventral and five transverse cirri. Some species have an extra satellite-like frontoventral cirrusmaking eight in total. Only A. mutans Kahl, 1932 and A. binucleata Kahl, 1932 have more thaneight frontoventral cirri. The extreme left hand cirrus of the five transverse cirri is frequently split,often into three, making seven in all. One species, A. polystyla, is consistently found with 11-15transverse cirri which the present authors regard as a reasonable specific character although ithas been suggested (Tuffrau, 1964) that it is the result of three of the original transverse cirrisplitting. IP Fig. 9 Cirri arrangement : (a) Aspidisca lynceus showing 'lynceus-arrangement' of the frontoventralcirri (after Kahl, 1932); (b) Aspidisca polystyla showing 'polystyla-arrangement' of the frontoventralcirri (after Tuffrau, 1964). The frontoventral cirri appear to be arranged in two basic patterns. One is as in A. lynceuswhere the seven frontoventral cirri are located within the anterior half of the ventral surface,with a row of four cirri running closely along the anterior right border and a row of three nearerthe centre (Fig. 9a). The second is as in A. polystyla which was the first species to be describedwith six of the seven frontoventral cirri in the anterior half of the ventral surface, in two groupsof three, and the remaining cirrus lying subequatorially in the posterior half of the body close tothe transverse cirri (Fig. 9b). These cirri have frequently been referred to as six frontals and oneventral. There is often a low projection ('lp' in Fig. 9) on the inner right border dividing the ventralsurface. These two patterns will be referred to as the 'lynceus-arrangement' and the 'polystyla-arrangement'. Where eight frontoventral cirri are observed, one cirrus is invariably satellite-likewhich does not affect the overall 'polystyla-arrangement' of the other seven cirri. Satellite-likecirri have been shown by Tuffrau (1964) and Deroux & Tuffrau (1965) to have distinct morpho-genetic origins. These authors studied the morphogenesis of the cirri of A. lyncaster and A.orthopogon respectively and numbered the cirri as did Wallengren (1900) for Euplotes (Fig.lOa & b). Their system is adopted throughout this revision. Although it is erroneous to regardsuch cirri as true 'satellites', which many workers have done, the term 'satellite-like', whileperhaps misleading, is probably most appropriate. A different morphogenetic pattern for thecirri and the AZM of A. costata was presented by Diller (1975) (Fig. lOc). The location of the transverse cirri is fairly uniform throughout the genus. They are generallyjust posterior to the peristome in a row curving towards the anterior on the right. In some species, 8 I. C. H. WU & C. R. CURDS the three transverse cirri on the right form an almost vertical row slightly apart from the othertwo cirri. It may be significant that the latter arrangement of the transverse cirri appears toassociate with frontoventral cirri in 'lynceus-arrangement' (see Fig. 11). IV, VI V IV III II I ! I Fig. 10 Numeration of ventral cirri by the Wallengren (1900) system of: (a) Aspidisca lyncasterafter Tuffrau, 1964 (called A. leptaspis in this revision); (b) A. orthopogon after Deroux & Tuffrau,1965; (c) A. lynceus after Diller, 1975. Diagnosis of Aspidisca Small (mostly 50-100 urn) hypotrichs. Body ovoid and rigid. Dorsal and right side convex.Ventral surface flattened. Dorsal surface may be smooth or conspicuously ridged. Left andposterior borders sometimes serrated. AZM in two parts. The posterior part is a system ofmembranelles lining the peristome while the anterior part (or anterior ciliary organelle) is com-prised of two to eight cilia. Seven to eight frontoventral cirri, five to twelve transverse cirri. Nomarginal or caudal cirri. Macronucleus horseshoe-shaped or in two rounded parts. Mostly marine,few euryhaline. Systematic description Keys to the genus Aspidisca The characters selected to separate the species are used in order of their reported stability. Thefirst division of species into groups is based on the number and arrangement of the frontoventralcirri. Further separations are based on the number of transverse cirri, presence of peristomialspur, presence of dorsal ribs and thorn, number of macronuclei and so on. Unless otherwisestated, all species described are marine, the sizes of organisms given in the text refer to theirlengths and scales drawn on diagrams indicate 10 um. Key to the major groups la 7 or 8 frontoventral cirri .b more than 8 frontoventral cirri 2 a frontoventral cirri in 'lynceus-arrangement'b frontoventral cirri in 'polystyla-arrangement' . SECTION C p. 27 SECTION A p. 9SECTION B p. 14 THE GENUS ASPIDISCA Fig. 11 Four Aspidisca species with lynceus-type ventral cirri arrangement (after Kahl, 1932):(a) A. cicada (called A. costata & A. sulcata in Kahl); (b) cross-section of (i) A. cicada (calledA. sulcata in Kahl); (ii) A. cicada (called A. costata in Kahl), (iii) longitudinal section of A. turrita;(c) A. turrita; (d) A. lynceus; (e) A. herbicola, ventral surface; (f) A. herbicola, dorsal surface. Section A Key to species with frontoventral cirri in 'lynceus-arrangement' 1 a with peristomial spur ...... b without peristomial spur ..... 2 a dorsal surface smooth ...... b dorsal surface with grooves, ribs and/or thorn. 3 a with dorsal thorn. ...... b without dorsal thorn ...... 4 a 3-10 conspicuous dorsal ribs. ....b indistinct dorsal grooves ..... 5 a 6 dorsal kineties bearing, from left to right 2:7:9:9:7b 5 dorsal kineties bearing, from left to right 3:6:6:3:2 6 a with dorsal thorn. ...... b without dorsal thorn : 7 ciliacilia . 62 A. lynceus3 A. turrita4 A. cicada5 A. lynceus A. cicada A. herbicola A. lyncaster Aspidisca lynceus (Miiller, 1773) Ehrenberg, 1830 Trichoda lynceus Miiller, 1773Aspidisca nana Tucolesco, 1962 10 I. C. H. WU & C. R. CURDS Fig. 12 , Aspidisca lynceus: (a & b) ventral & dorsal silver-line systems after Klein, 1929; (c & d)ventral surface & diagrammatic cross-section after Bick, 1972; (e & f) ventral & dorsal silver-linesystems after Gelei, 1939; (g & h) ventral view & nucleus (called A. nana in Tucolesco, 1962). This species was first described by Miiller (1773) as Trichoda lynceus and was transferred to thegenus Aspidisca by Ehrenberg (1830) as the type species. It is probably the most studied andwidespread species of the genus and its general morphology has been described in detail byClaparede & Lachmann (1858), Stein (1859), Kahl (1932), Gelei (1939) and Bick (1972). Klein(1929) was the first to describe the silver-line system stained by the dry-silver method. Gelei (1939)also used the silver-impregnation technique but illustrated a silver-line system different to thatshown by Klein. The original specimens were described from freshwater but others have beenfound in marine and freshwater habitats from various parts of the world. DIAGNOSIS. Aspidisca lynceus (Figs lid & 12) is a small (30-50 um) species found in all typesof water where decomposition of organic material takes place, frequently in activated sludge.The typical features are oval body with straight left border and convex right border, smoothoutline, seven frontoventral cirri, five transverse cirri, 10-15 membranelles in the posterior AZMand three to four cilia in the anterior ciliary organelle, a horseshoe-shaped macronucleus and aspherical micronucelus. The arrangement of the cirri is typical of a group of four species, A. cicada,A. herbicola, A. lynceus and A. turrita (Fig. 11). The frontoventral cirri are in two rows, of fourand three cirri, near the anterior border; two of the five transverse cirri are immediately posteriorto the peristome while the other three are slightly apart on the right and are almost verticallyaligned. Kahl (1932) and Bick (1972) have noted a distinct spike-like projection separating theextreme left pair of transverse cirri in A. lynceus and this is also found in A. turrita (Figs lie THE GENUS ASPIDISCA 11 6 d, 12c). A smooth dorsal surface distinguishes A. lynceus from A. cicada which has dorsal ribs,but Stein (1859) noted three feeble dorsal furrows on his specimens of A, lynceus, while Hamm(1964) noted that the ribs of A. cicada are sometimes indistinct in which cases the separation ofA. lynceus from A. cicada relied upon the dorsal silver-line system. The silver-line system ofA. lynceus, according to Klein (1929), consists of two lateral peripheral kinetics which meetanteriorly encircling three central longitudinal kinetics and a short kinety on their right whichextends only to the posterior half of the body. The kinetics carry, from left to right, 2:7:9:9: 7 : 7 cilia (Fig. 12b). Fig. 13 Aspidisca turrita: (a-c) ventral, dorsal & dorsolateral view after Stein, 1859; (d & e) ventral& lateral view after Claparede & Lachmann, 1858; (f) after Kahl, 1932; (g-j) dorsal thorns(called Euplotes turritus in Ehrenberg, 1838). Aspidisca turrita (Ehrenberg, 1838) Claparede & Lachmann, 1858Euplotes turritus Ehrenberg, 1838 Ehrenberg (1838) first discovered this species, which is characterised by the presence of a dorsalthorn, among seaweeds in Berlin and later in freshwater together with A. lynceus. He named thisorganism Euplotes turritus but Claparede & Lachmann (1858) transferred it to the genusAspidisca and emended the specific name to turrita. The latter authors noted that the dorsal thornon their specimens found near Berlin was more prominent than that reported by Ehrenberg.The species was redescribed by Stein (1859), Plough (1916) and Kahl (1928, 1932). Kahl (1932)noted that its shape and ciliature are completely identical to those of A. lynceus and that theremay be ribs as well as a thorn on the dorsal surface which itself may vary in size or be missing.Further studies may prove the dorsal thorn to be a transitional appendage, in which caseA. turrita should be regarded as a synonym of A. lynceus. 12 I. C. H. WU & C. R. CURDS DIAGNOSIS. Aspidisca turrita (Figs lie & 13) is a euryhaline species and its morphology isalmost identical to the type species A. lynceus. It is small (20-30 jam), the body is oval but convexon the right and the outline is smooth. There are seven frontoventral cirri in 'lynceus-arrangement'and, as in A. lynceus, two of the five transverse cirri are found posterior of the peristome separatedby a 'spike'. The other three transverse cirri are aligned almost vertically near the right border.The macronucleus is C-shaped. A curved, pointed dorsal thorn distinguishes this from the typespecies. Aspidisca cicada (Miiller, 1786) Claparede & Lachmann, 1858 Trichoda cicada Miiller, 1786 Coccudina cicada Bory, 1 827 Coccudina crassa Dujardin, 1841 Aspidisca costata (Dujardin, 1841) Stein, 1859 Aspidiscopsis bengalensis Ghosh, 1921 Aspidisca marsupialis Penard, 1921 Aspidisca sulcata Kahl, 1932 Aspidisca costata f. tetracirrata Tucolesco, 1962 The taxonomic history of this species is one of confusion and misidentifications. Brown (1966)studied the species and subsequently (Brown, 1968) gave a complete historical account of thenomenclature of the species but the confusion remained. A recent account and redescription ofthe species was given by Curds (1977). Briefly, the original freshwater specimens were described by Miiller (1786) and named Trichodacicada which Bory (1827) then transferred to the genus Coccudina. Claparede & Lachmann(1858) placed T. cicada Miiller in the genus Aspidisca. Stein (1859) first synonymised Coccudinacostata Dujardin, 1841 with Aspidisca cicada Claparede & Lachmann, 1858. However, the dorsalribs of the former species were described as being crenated while those of the latter species weresaid to be smooth. Later workers including Plough (1916), Kahl (1932), Hamm (1964), Bick (1972)and Diller (1975) perpetuated the error and described A. cicada (Miiller, 1786) Claparede &Lachmann, 1858 under the name A. costata (Dujardin, 1841) Stein, 1859. Borror (1972) alsolisted A. cicada as a synonym of A. costata and Trichoda cicada as a synonym of A. lynceus. DIAGNOSIS. Aspidisca cicada (Fig. 14) is a small (20-45 urn) euryhaline species similar to thetype species A. lynceus and equally widely distributed. The oval body is convex on the right andthere are seven frontoventral and five transverse cirri. The frontoventral cirri are in 'lynceus-arrangement' and a projection separating the second and third transverse cirri from the left hasbeen noted by Bick (1972) and Curds (1977). The body outline is smooth but the peristomesometimes form a 'swelling' at the posterior left. There are about eight membranelles in theposterior AZM and three anterior cilia. The dorsal surface is conspicuously ridged by longitudinalribs varying in size and number (within the three to ten range). The macronucleus is C-shaped andthe micronucleus is at its anterior left. The dorsal silver-line system consists of two centrallongitudinal kinetics and on their right a short kinety extending only to the posterior third of thebody, encircling these are two outer kinetics which runs along the periphery and meet anteriorly.The five kinetics, from left to right, carry 3:6:6:3:2 cilia. Aspidisca herbicola Kahl, 1932 This species has been described once briefly and it is the only species that has not yet been foundin marine habitats. DIAGNOSIS. Aspidisca herbicola (Fig. lie & f) is a small (50 urn) freshwater species. The peris-tomial spur and the four dorsal ribs, one bearing a thorn, distinguish this from the type species.The seven frontoventral cirri are in 'lynceus-arrangement'. The transverse cirri are arrangedexactly like those of A. lynceus except that the two cirri on the left are not separated by a 'spike'.There are about ten membranelles in the posterior AZM and three anterior cilia. THE GENUS ASPIDISCA 13 n Fig. 14 Aspidisca cicada: (a-e) after Curds, 1977; (f) after Bick, 1972 (called A. costata); (g-i)after Claparede & Lachmann, 1858; (j-k) after Stein, 1859 (called A. costata); (1) after Dujardin,1841 (called Coccudina crassa); (m-n) after Tucolesco, 1962 (called A. costata f. tetracirratd);(o-q) after Penard, 1921 (called A. marsupialis); (r) after Ghosh, 1921 (called Aspidiscopsisbengalensis). Aspidisca lyncaster (Miiller, 1779) Stein, 1859 Trichoda lyncaster Miiller, 1779Kerona lyncaster Miiller, 1786 This species was first briefly described as Trichoda lyncaster by Miiller in 1779 and later (1786)he transferred it to the genus Kerona. Stein (1859), by fixing the animals, gave a more detailed 14 I. C. H. WU & C. R. CURDS description of the specimens collected from seawater of Stralsundt, and later from TravemUnde.The species was transferred to the genus Aspidisca by Stein in 1859. Plough (1916) redescribedthe species in his work but later workers, including Kahl (1932), Dragesco (1960) and Tuffrau(1964), described organisms under the name A. lyncaster, which the present authors wouldregard as A. leptaspis. DIAGNOSIS. Aspidisca lyncaster (Fig. 15) is a small (30-50 urn) species. It is almost egg-shaped,slightly pointed posteriorly. On the left border there is a conspicuous peristomial spur and asmaller anterior projection. There are seven frontoventral cirri in 'lynceus-arrangement' whichdistinguishes this species from A. leptaspis, five transverse cirri, an extensive peristome and twoto three cilia in the anterior ciliary organelle. The dorsal surface is marked by three longitudinalridges and the macronucleus is horseshoe-shaped. a / \ ^ b Fig. 15 Aspidisca lyncaster: (a) ventral surface; (b) dorsal surface (after Stein, 1859). Section B Key to species with frontoventral cirri in 'polysty la-arrangement' THE GENUS ASPIDISCA 10 a 2 macronuclei .....b single macronucleus .... 11 a without peristomial spur (with V/3 cirrus)b with peristomial spur (with VI/2 cirrus) 12 a dorsal surface with smooth ridgesb dorsal surface with crenated ribs . 15 A. fuscaA. sedigita A. orthopogon 12 A. leptaspisA. pule her rima a Fig. 16 Aspidisca poly sty la: (a) after Tuffrau, 1964; (b) after Stein, 1859;(c) after Pereyaslawzewa, 1886 (called A, pland). Aspidisca polystyla Stein, 1859A spidisca plana Pereyaslawzewa, 1886 The original study of this species by Stein (1859) was very detailed and he characterised thespecies by the presence of a large number of transverse cirri. Most of the original specimens had10-1 1 transverse cirri but some had 12, up to 15 have been observed in later studies. Plough (1916),Kahl (1932) and Tuffrau (1964) all described the species and Tuffrau mentioned the silver-linesystem. Dragesco (1963) described an organism which he regarded as A. polystyla possessing onlyfive transverse cirri, but the present authors consider this specimen to be A. steini. DIAGNOSIS. Aspidisca polystyla (Fig. 16) is a small (40-50 urn) species characterised by 10-15transverse cirri. The body outline is smooth and the dorsal surface is marked by three longi-tudinal ridges. The arrangement of the seven frontoventral cirri is diagnostic : two rows of threecirri are found near the anterior while one cirrus is found near the transverse group. There areabout 15 membranelles in the posterior AZM and two to six anterior cilia. The macronucleus ishorseshoe-shaped but no micronucleus has been observed. The dorsal silver-line system wasdescribed by Tuffrau (1964) as consisting of four kinetics with hexagonal links as in Euploteseurystomus but no illustration was provided. Aspidisca major (Madsen, 1931) Kahl, 1932 Onychaspis (Aspidisca) steini var. major Madsen, 1931Aspidisca steini var. major (Madsen, 1931) Kahl, 1932Aspidisca major var. faurei Dragesco, 1960 Madsen (1931) described this species as Onychaspis (Aspidisca) steini var. major which was dis-tinguished from A. steini Buddenbrock, 1920 by its larger size. The description was brief and therewas no mention of nuclei. Kahl (1932) redescribed this species as Aspidisca (Onychaspis) steinivar. major and listed Aspidisca major Madsen (?) with two macronuclei as a separate species. 16 I. C. H. WU & C. R. CURDS Kahl separated A. steini var. major and A. major by the difference in number and disposition ofthe anterior cilia. Tuffrau (1964) later described A. major Madsen (?) which is almost identical tothe Onychaspis (Aspidiscd) steini var. major of Madsen (1931) and had two macronuclei. Tuffraunoted that the two macronuclei were connected by a nuclear membrane, and in A. major var.faurei Dragesco, 1960 they appear to be joined more completely. However, in both cases thereare two distinct nuclear elements. Fig. 17 Aspidisca major: (a) after Tuffrau, 1964; (b) after Madsen, 1931 (called Onychaspis(Aspidisca) steini var major); (c) after Kahl, 1932; (d) after Dragesco, 1960 (called A. major varfaurei); (e) nuclear features after Dragesco, 1960. DIAGNOSIS. Aspidisca major (Fig. 17) is a medium size (60-100 urn) oval species with perfectlysmooth borders and a smooth dorsal surface. The seven frontoventral cirri are in 'polystyla-arrangement' and the five transverse cirri are long. The group of one to four anterior cilia isfound just anterior of the II/3 cirrus as in A. steini. The peristome, with about 15 membranellesin the posterior AZM, is small relative to the body size. There are two ellipsoid macronucleiwhich may be connected by a nuclear membrane. The dorsal silver-line system consists of fourrows of sensory bristles with transverse links forming regular polygons as in A. polystyla andEuplotes-eurystomus (Tuffrau, 1964). Aspidisca steini Buddenbrock, 1920 Aspidisca glabra Kahl, 1928 Aspidisca hyalina Dragesco, 1954 [Aspidisca polystyla Stein; Dragesco, 1963 Misidentification] The original specimens of this species were found in a marine aquarium in Germany. Buddenbrock(1920) pointed out the possibility of it being a variety of A. polystyla Stein which differs only inhaving many more transverse cirri. However, it was later found that the two species could bedistinquished by their silver-line systems. Kahl (1932) inadequately redescribed the species, butBorror (1963) found an organism of similar shape and ciliature in N. America which he identifiedas A. steini and gave data concerning its size, micronucleus and dorsal kinetics for the first time. THE GENUS ASPIDISCA 17 DIAGNOSIS. Aspidisca steini (Fig. 18) is a small (30-35 urn) species characterised by its smoothoutline and smooth dorsal surface. The seven frontoventral cirri are in 'polystyla-arrangement'and the extreme left cirrus of the five transverse cirri may be double-based or split into twomaking six transverse cirri. There are eight to nine membranelles in the posterior AZM and theanterior ciliary organelle containing two to four cilia is positioned just anterior to the II/3 cirrus.The macronucleus is C-shaped and the spherical micronucleus is located on its left. There arefive dorsal kinetics carrying, from left to right, 2:4:5:5:4 cilia respectively. Fig. 18 Aspidisca steini: (a & b) ventral surface & dorsal silver-line system after Borror, 1963;(c-e) after Buddenbrock, 1920; (f) after Kahl, 1928 (called A. glabra); (g-h) after Dragesco, 1954(called A. hyalina); (i) after Dragesco, 1963 (called A. polystyla). Aspidisca aculeata (Ehrenberg, 1838) Kahl, 1932 Euplotes aculeata Ehrenberg, 1838Onychaspis aculeata Manseld, 1923 Ehrenberg (1838) first discovered this small species with a dorsal 'backward curving hook' inseawater at Kiel which he called Euplotes aculeata Ehrenberg, 1838. The original diagrams werecrude and practically identical to those of Euplotes turritus Ehrenberg, 1838. Mansfeld (1923)found in an aquarium in Berlin a hypotrich, Onychaspis aculeata, with a dorsal thorn similar toAspidisca turrita (Ehrenberg, 1838) Claparede & Lachmann, 1858 but differing in having dorsalribs as well as a thorn. Kahl later (1932) identified it as Euplotes aculeata Ehrenberg and trans-ferred it to the genus Aspidisca. Borror (1965) and Agamaliev (1974) redescribed the species ingreater detail, stained the silver-line system and noted up to three micronuclei. The arrangementof the frontoventral cirri of Onychaspis aculeata illustrated by Mansfeld appears to be differentfrom the two usual patterns but we consider the illustrations by the later authors more reliable. 18 I. C. H. WU & C. R. CURDS Fig. 19 Aspidisca aculeata: (a-c) after Agamaliev, 1974; (d) after Kahl, 1932; (e-f) after Ehrenberg,1838 (called Euplotes aculeata); (g-k) after Mansfeld, 1923 (called Onychaspis aculeata); (1-p)after Borror, 1965. DIAGNOSIS. Aspidisca aculeata (Fig. 19) is a small (30-50 jam) species with seven frontoventralcirri in 'polystyla-arrangement' which distinguishes it from Aspidisca turrita, and five or sixtransverse cirri. The body is oval, slightly convex on the right, and the outline is smooth. Dorsallythere are four ribs, the second from the left of which carries a thorn. The macronucleus is (T--shaped and one to three micronuclei may be found by its anterior left. The peristome is averagein size with about ten membranelles in the posterior AZM and there are three to five anteriorcilia. The silver-line system, according to Agamaliev (1974), consists of five dorsolateral kineticswith single cross-links, and the four dorsal kinetics carry, from left to right, 4:5:6:8 ciliarespectively; while Borror (1965) found no lateral kinetics and the four dorsal kinetics carry,from left to right, 5:5:5:6 cilia respectively and a few cross-links were noted. THE GENUS ASPIDISCA Aspidisca tuberosa Kahl, 1932 19 Oxytricha cicada Ehrenberg, 1838Coccudina costata Dujardin, 1 841 The description of this species by Kahl (1932) is brief but the ventral ciliature and the crenateddorsal ribs are clearly illustrated. A small, smooth-bordered hypotrich with crenated ribs wasdescribed as Oxytricha cicada by Ehrenberg, 1838, and was considered by Dujardin (1841) to besimilar to Coccodina costata. Since the specific name cicada is preoccupied, the correct combina-tion for this taxon should be Aspidisca costata. But, due to a long history of misuse of this com-bination when describing A. cicada (Miiller, 1786) Claparede & Lachmann, 1858 (see p. 12), thepresent authors refrain from making this emendation. Fig. 20 Aspidisca tuberosa: (a-b) after Kahl, 1932; (c-d) after Dujardin, 1841 (called Coccudinacostata); (e-g) after Ehrenberg, 1838 (called Oxytricha cicada). DIAGNOSIS. Aspidisca tuberosa (Fig. 20) is a small (30-35 urn) species characterised by four tosix crenated sharp dorsal ribs. Its body shape is typical of the genus, oval and convex on the right.There are seven frontoventral cirri in 'polystyla-arrangement', six transverse cirri, three cilia inthe anterior ciliary organelle and ten membranelles in the posterior AZM. Aspidisca polypoda (Dujardin, 1841) Kahl, 1932 Coccudina polypoda Dujardin, 1841 Aspidisca andreewi Mereschowsky, 1878 Aspidisca poly sty la naz maxima Gourret & Roeser, 1886 Aspidisca quadrilineata Kahl, 1932 This species characterised by seven or eight conspicuous dorsal ribs was first described by Dujardin(1841). Kahl (1932) clearly illustrated the dorsal ribs and the ventral cirri of specimens fromHeligoland and transferred the species to the genus Aspidisca. Dragesco (1960) described some-what larger organisms from Roscoff which he identified as A. polypoda but made no mention ofthe characteristic dorsal ribs. The latter author also described the nuclei and mentioned that 'letegument de ce cilie montre une fine structure superficielle, constituant un veritable reseau amailles fines' but presented no diagrams of these. As in the case of A. lynceus and A. cicada, adistinctive silver-line system would be a more precise feature for separating A. polypoda fromA. steini rather than just the presence of dorsal ribs. DIAGNOSIS. Aspidisca polypoda (Fig. 21) is a small (30-55 um) species with seven or eightdistinctive dorsal ribs which distinguishes it from A. steini, and the 'polystyla-arrangement' ofthe seven frontoventral cirri distinguishes it from A. cicada. Six transverse cirri are generally 20 I. C. H. WU & C. R. CURDS noted. The peristome is small with 8-15 membranelles in the posterior AZM and there are threeto four anterior cilia. The macronucleus is described as a horseshoe-shaped opening towards theposterior right and the spherical micronucleus is found in the opening (Dragesco, 1960). Aspidisca dentata Kahl, 1928 This species has been described only by Kahl (1928, 1932) and it was found extensively in Oldesloe,Kiel and the North Sea but not in large numbers. Fig. 21 Aspidisca polypoda : (a-c) after Kahl, 1932; (d) after Dragesco, 1960; (e-g) after Dujardin,1841 (called Coccudina polypoda); (h) after Mereschkowsky, 1878 (called A. andreewi); (i-j) afterGourret & Roeser, 1886 (called A. polystyla var maxima). DIAGNOSIS. Aspidisca dentata (Fig. 22) is a small (20-40 um) species. It has four dorsal ribs,one of which bears a thorn. There are seven frontoventral cirri in 'polystyla-arrangement', sixtransverse cirri, six to ten membranelles in the posterior AZM and four anterior cilia. The presenceof a peristomial spur separate this from the almost identical species Aspidisca aculeata. Aspidisca magna Kahl, 1932 Aspidisca pelvis Delphy, 1938 Aspidisca maxima Vacelet, 1961 (see Vacelet, 19616) The original description of this species by Kahl (1932) was inadequate as only six to eight speci-mens were observed. However, its large size is distinctive. Tuffrau ( 1 964) described an equally large THE GENUS ASPIDISCA 21 Fig. 22 Aspidisca dentata: (a & b) ventral & dorsal surface after Kahl, 1932;(c) ventral surface after Kahl, 1928. species which also possessed a peristomial spur and this he identified as A. magna. AlthoughTuffrau used silver-impregnation techniques, only a vague description of the dorsal silver-linesystem was given. DIAGNOSIS. Aspidisca magna (Fig. 23) is the largest (135-157 um) species described. The bodyis broadly oval and its outline is broken only by a broad conspicuous peristomial spur. There arefour ribs on the dorsal surface and the central ones of these are higher than the lateral ones. Theseven frontoventral cirri are in 'polystyla-arrangement' and there are five or six transverse cirri.The peristome is small in proportion to the body size with about 20 membranelles in the posterior Fig. 23 Aspidisca magna: (a) after Tuffrau, 1964; (b-c) after Kahl, 1932; (d-e) after Delphy, 1938(called A. pelvis); (f) after Vacelet, 19616 (called A. maxima). 22 I. C. H. WU & C. R. CURDS AZM and there are six anterior cilia. The macronucleus is a slim horseshoe but no micronucleushas been noted. The dorsal argyrome pattern is described as 'classic' with four kinety meridiansjoined by simple transverse links (Tuffrau, 1964). Fig. 24 Aspidisca fusca: (a-b) after Agamaliev, 1967; (c) after Kahl, 1932; (d) after Burkovsky,1970; (e) after Burkovsky, 1970 (called A. irinae); (f-g) after Dragesco, 1965. Aspidisca fusca Kahl, 1928Aspidisca irinae Burkovsky, 1970 This species was first found in Oldesloe, Kiel. In the original description, Kahl (1928) did notmention the nuclei but Dragesco (1965) identified specimens from Port Etunnie and reported thepresence of two macronuclei. Agamaliev (1967) was unsuccessful in silver-impregnating thedorsal argyrome of specimens from the Caspian Sea but successfully stained the ventral cirri anda lateral kinety. Burkovsky (1970) described A. fusca with frontoventral cirri in an uncharacteris-tic arrangement which the present authors would question. In the same paper Burkovsky des-cribed a new species A. irinae which is practically identical to A. fusca and is here regarded as asynonym. DIAGNOSIS. Aspidisca fusca (Fig. 24) is a small to medium size (40-60 urn) species. The body isoval, slightly convex on the right, and the dorsal surface is arched and smooth. There are sevenfrontoventral cirri in 'polystyla-arrangement' and five transverse cirri. The peristome is small THE GENUS ASPIDISCA 23 with 10-12 membranelles in the posterior AZM and there are four to six anterior cilia. Twocentrally located oval macronuclei are arranged in an inverted 'V shape with a spherical micro-nucleus situated between. The prominently developed peristomial spur distinguishes this speciesfrom A. major. Aspidisca sedigita Quennerstedt, 1867 Aspidisca hexeris Quennerstedt, 1869Aspidisca crenata Fabre-Domerque, 1869Aspidisca angulata Bock, 1952Aspidisca pertinens Bock, 1955Aspidisca fjeldi Dragesco, 1960Aspidisca tridentata Dragesco, 1963Aspidisca caspica Agamaliev, 1967Aspidisca fuscoides Agamaliev, 1975 Aspidisca sedigita is in almost every respect like Aspidisca leptaspis described by Fresenius twoyears earlier, but the absence of a VI/2 cirrus distinguishes A. sedigita from the earlier species.The four species A. hexeris, A. crenata, A. pertinens and A. fjeldi are all of similar size, shapeand ciliature to A. sedigita but have been designated as separate species since they have only oneor no projection on the left border other than the peristomial spur. As we do not consider lateralprojections to be stable taxonomic features the above listed species are regarded as synonyms ofA. sedigita. The two species A. tridentata and A. caspica both have three dentations on the leftborder are undoubtedly identical to A. sedigita. DIAGNOSIS. Aspidisca sedigita (Fig. 25) is a medium size (50-100 um) species. Its shape is typicalof the genus, oval and convex on the right. On the left border is a prominent peristomial spurand one or two smaller projections. The posterior border may be serrated and the dorsal surfaceis marked by two to four grooves. There are seven frontoventral cirri in 'polystyla-arrangement'and six to seven transverse cirri. The peristome is of average size and there are four to eightanterior cilia. The macronucleus is horseshoe-shaped and up to three micronuclei have beenobserved. According to the description of A. caspica by Agamaliev (1967, 1970), the silver-linesystem consists of five dorsolateral kinetics carrying a variable number of cilia and the argyromepattern is also variable. Aspidisca orthopogon Deroux & Tuffrau, 1965 This species has been described only by Deroux & Tuffrau (1965) who gave a detailed account ofthe morphogenesis of the ventral ciliature. DIAGNOSIS. Aspidisca orthopogon (Fig. 26) is one of the few larger (80-110 urn) species of thegenus. Its outline is smooth and the body a perfect oval without being convex on the right, as istypical of the genus. Other than seven frontoventral cirri in 'polystyla-arrangement', it has asatellite-like V/3 cirrus (also named 'cirre surnumeraire' by Deroux & Tuffrau, 1965) and not theVI/2 cirrus found in the other species with eight frontoventral cirri. Its peristome with 40-50membranelles in the posterior AZM is uniquely extensive and there are four anterior cilia. Themacronucleus is a classic horseshoe and the micronucleus is by its anterior left. The silver-linesystem consists of four symmetrically aligned dorsal kinetics each carrying more than 30 cilia,and simple transverse links forming a 'draught-board' pattern. Aspidisca leptaspis Fresenius, 1865 Aspidisca psammobiotica Burkovsky, 1970 [Aspidisca lyncaster Stein; Kahl, 1932 Misidentification][Aspidisca lyncaster Stein; Dragesco, 1960 Misidentification][Aspidisca lyncaster Stein; Tuffrau, 1964 Misidentification] 24 I. C. H. WU & C. R. CURDS Fig. 25 Aspidisca sedigita: (a) after Quennerstedt, 1867; (b) after Quennerstedt, 1869 (calledA. hexeris); (c-d) after Bock, 1952 (called A. angulatd); (e) after Fabre-Domerque, 1885 (calledA. crenata); (f-g) after Bock, 1955 (called A.pertinens); (h-i) after Dragesco, 1960 (called A.fjeldi);(j) after Dragesco, 1963 (called A. tridentata); (k-m) after Agamaliev, 1967 (called A. caspica);(n-p) after Agamaliev, 1975 (called A.fuscoides). [Aspidisca sedigita Quennerstedt; Kahl, 1932 Misidentification][Aspidisca sedigita Quennerstedt; Dragesco, 1960 Misidentification] Fresenius (1865) found a large and a small (30-35 um) Aspidisca in a seawater acquarium. Hestated that the former was similar to A. lyncaster and described the latter as A. leptaspis. SinceKahl (1932) found large specimens of the latter species, it is likely that Fresenius described twodifferent size groups of the same species. There are eight frontoventral cirri illustrated in Fresenius's THE GENUS ASPIDISCA 25 diagram which we consider are a major diagnostic feature. Two species, A. lyncaster (Muller)Stein and A. sedigita Quennerstedt, have been described with similar ciliature but only sevenfronto ventral cirri. Tuffrau (1964) described the silver-line system of what he identified as A.lyncaster but with eight front oventral cirri and it is similar to that of A. leptaspis illustrated byAgamaliev (1974). Fig. 26 Aspidisca orthopogon: (a) ventral ciliature; (b) nuclei; (c) dorsal silver-line system (after Deroux & Tuffrau, 1965). DIAGNOSIS. Aspidisca leptaspis (Fig. 27) is a small to medium size (30-90 um) species. It ischaracterised by the presence of a prominent peristomial spur and a satellite-like VI/2 cirruswhich together with seven other frontoventral cirri in 'polystyla-arrangement' make a total ofeight. One or two small dentations may be found at the anterior left and serrations on the posteriorborder. There are five or six transverse cirri and three or four dorsal ribs. The peristome is fairlyextensive accommodating about 1 5 membranelles in the posterior AZM and the anterior ciliaryorganelle consists of six to eight cilia. The macronucleus is a perfect horseshoe and two micro-nuclei have been seen. The silver-line system is of five dorsolateral kinetics, the dorsal kinety onthe extreme right hand runs along the border and joins the two central kinetics anteriorly. Simpletransverse links join the kinetics. The longest dorsal kinety on the right carries about 20 cilia(see Agamaliev, 1974). Aspidisca pulcherrima Kahl, 1932 Aspidisca pulcherrima var. baltica Kahl, 1932Aspidisca baltica Borror, 1965 This species was originally described from the North Sea by Kahl (1932). Tuffrau (1964) identifiedthis species from Roscoff and described its silver-line system but did not mention any crenateddorsal ribs which is a distinctive feature described by Kahl (1932). Kahl (1932) also describeda variety, A. pulcherrima var. baltica, on the seaweed Ulva in the Baltic Sea which he consideredhad a less serrated posterior border and the dorsal ribs bore 'humps' rather than 'teeth'. Borror(1965) redescribed this variety and raised it to species level for similar reasons, noting that it alsohad a distinct configuration of the 'right lip of the buccal cavity' and ventral argyromes. Sincewe do not consider these features as diagnostic characters this variety is treated as a synonym.Borror (1965) also illustrated the silver-line system which agrees with that given by Tuffrau (1964). DIAGNOSIS. Aspidisca pulcherrima (Fig. 28) is a medium size (70-90 um) species characterisedby four crenated dorsal ribs and a rugged body outline. Apart from a prominent peristomial spur,there may be two smaller projections on the anterior left border. Along the posterior border are 26 I. C. H. WU & C. R. CURDS m Fig. 27 Aspidisca leptaspis: (a-c) after Agamaliev, 1974; (d-e) after Fresenius, 1865; (f) after Kahl,1932; (g-h) after Burkovsky, 1970 (called A. psammobioticd); (i) after Kahl, 1932 (called A.lyncaster);(i) after Dragesco, 1960 (called A. lyncaster}; (k) after Tuffrau, 1964 (called A. lyncaster);(1) after Kahl, 1932 (called A. sedigita); (m) after Dragesco, 1960 (called A. sedigita). three to four pronounced dentations and the posterior half of the right border is also slightlyserrated. There are six or seven transverse cirri and seven frontoventral cirri in 'polystyla-arrange-ment' plus a satellite-like VI/2 cirrus making eight in all. The macronucleus is C-shaped with oneor two micronuclei at its immediate left. There are 15-20 membranelles in the posterior AZM andfour to eight anterior cilia. The silver-line system consists of four kinety meridians and simpleirregular transverse links. THE GENUS ASPIDISCA 27 9 h Fig. 28 Aspidisca pulcherrima: (a-b) after Kahl, 1932; (c) after Tuffrau, 1964; (d-e) after Kahl,1932 (called A. pulcherrima var baltica); (f-h) after Borror, 1965 (called A. balticd). Section C Key to species with more than eight frontoventral cirri 1 a 11-15 frontoventral cirri and a keel-like dorsal spineb 9 frontoventral cirri and 2 macronuclei . A. inn tansA. binucleata Aspidisca mutatis Kahl, 1932 The large number of cirri on the ventral surface and the keel-like dorsal spine of A. mutans areunique to the genus. The description of this species from Kiel is the only source of information. DIAGNOSIS. Aspidisca mutans (Fig. 29) is a large (90-150 urn) species. The oval body is convexon the right and the outline is smooth. It has 1 1-15 frontoventral cirri aligned in two rows each 28 I. C. H. WU & C. R. CURDS Fig. 29 Aspidisca mutans: (a) ventral surface; (b) dorsal surface; (after Kahl, 1932). with five to seven, and six to eight cirri. A satellite-like cirrus by the anterior right border andseven to eight transverse cirri make a total of up to 24 cirri on the ventral surface. The two ovalmacronuclei are small and are located anteriorly. The micronucleus is at the apex of the inverted'V formed by the macronuclei. There is a keel-like spine dorsally which may 'vary in its acutenessbut is seldom absent'. Aspidisca binucleata Kahl, 1932 The description of this species by Kahl is brief. A. binucleata differs from A. major only in havingnine frontoventral cirri instead of seven. DIAGNOSIS. Aspidisca binucleata (Fig. 30) is a medium size (70-90 um) species and the outlineof the oval body is smooth. There are nine frontoventral cirri, six transverse cirri, 15-20 mem-branelles in the posterior AZM and four anterior cilia. The two small round macronuclei and amicronucleus on their right are found in the anterior half of the body. Doubtful species Aspidisca caudata Vacelet, 1961 This species (Fig. 31) found at the marine station of Endorome-Marseille is 50-65 um long. Thereare two dentations on the left border, seven frontoventral cirri in 'polystyla-arrangement', five Fig. 30 Aspidisca binucleata after Kahl, 1932. THE GENUS ASPIDISCA 29 transverse cirri and a horseshoe macronulceus which are diagnostic features of A. sedigita.Vacelet (196 la) noted a tail-like structure which did not function as a flagellum nor as a ciliumbut trailed behind, and sometimes the animal seemed to be attached to the substrate by this 'tail'.Vacelet stated, however, that the rare individuals were briefly seen once on the surface of asediment sample, therefore the present authors are reluctant to regard this as a distinct speciesuntil further confirmation and information on this tail-like structure become available. a Fig. 31 Aspidisca caudata: (a) ventral surface; (b) nuclei (after Vacelet, 1961a). Nomena nuda Aspidisca bipartita Gourret & Roeser, 1886Aspidisca denticulata Ehrenberg, 1838Aspidisca pulvinata Fromentel, 1874Aspidisca radiata Fromentel, 1874Aspidisca robusta Kahl, 1932 Appendix 1 Plough's key for identification of the species of Aspidisca (Plough, 1916) A. Right and left border smooth ......... B. Left border incised to form a single backwardly directed spur in the posterior third C. Left border with two spurs, one in the anterior and one in the posterior third D. Left border with three spurs .......... a. Dorsal surface with recurved thorn-like appendage ..... Dorsal surface without thorn ......... c. Dorsal surface and posterior border serrated ...... Dorsal surface smooth .......... a' Ventral plate projecting beyond left border of carapace .... Ventral plate not projecting ......... a" Peristome reaching anterior border, anal cirri five ..... Peristomial cilia not reaching anterior border, anal cirri more than five a A. hexeris A. sedigita A. turrit a* a' A. leptaspis A. lyncaster A. costata* a" A. lynceusA. poly sty la * Indicates the only forms so far reported in freshwater. 30 I. C. H. WU & C. R. CURDS Appendix 2 Kahl's key for the identification of species of Aspidisca (translated from Kahl, 1(14) Freshwater, always with five transverse cirri .... 2 (5) Transverse cirri in an oblique row at or near the posterior border 3 (4) Transverse cirri at posterior border, only five ventral cirri . 4 (3) Transverse cirri near posterior border, dorsal with four delicate streaks .......... 5 (2) Transverse cirri far from the posterior border, the three right transverse cirri are on a ledge ...... 6 (9) The two left transverse cirri are divided at their base by a promi- nent spike. ......... 7 (8) Dorsal entirely smooth, without ribs and thorns 8 (7) Dorsal with a thorn arched towards the posterior, the remain surface flat or with delicated longitudinal ribs 9 (6) The two left transverse cirri are not divided by a spike 10(1 1) + Ventral plate forms a tooth on the left, dorsally there are four ribs,of these, the second from the left almost always bears a thorn . 11(10) Ventral plate without tooth on the left, no thorn dorsally butthere are three to six ribs 12(13) Small, almost always strongly arched form with six dorsal ribs .13(12) Somewhat larger species with three tall dorsal ribs .14 (1) Marine species, almost always with six transverse cirri 1 5(34) No teeth on the left of peristome (one species with five transversecirri exhibit a tooth adjacent to the flattened side) 16(19) Five transverse cirri . . . ... 17(18) Next to the peristome on the left, one finds turning of the body,nevertheless, the tooth lies visible ..... 18(17) No lateral tooth next to the peristome ..... 19(16) More than five transverse cirri ...... 20(33) Six transverse cirri ........ 21(22) Moderately large flat form with two rounded nuclei (also un-coloured towards the rim) and nine frontoventral cirri . 22(21) Small differently shaped species, always with seven ventral cirri. 23(24) Dorsally are four ribs varying in height, the second from the leftof these is almost always long, it bears a very variable thorn . 24(23) Dorsal without thorn, entirely flat or with ribs 25(26) Dorsal flat 26(25) Dorsal with ribs 27(28) Dorsal surface strongly arched, with eight clearly marked ribs,posterior edge of the peristome has projection directed back . 28(27) Flattened, with five to six weak ribs .....29(30) The peristomial deck forms a prominent triangle 1932) 2 3 Aspidiscopsis bengalensis A. marsupialis6 7A. lynceus A. turrita . 10 A. herbicola . 12A. costataA. sulcata . 15 . 16. 17 A.fusca A. majorA. steini var. major . 20. 21 A. binucleata . 23 A. aculeata . 25A. steini . ' . 27 A. polypoda . 29 A. andreewi THE GENUS ASPIDISCA 30(29) The posterior edge of the peristome forms a short blunt tooth,this projects back towards the two left transverse cirri . 31(32) The four (or six) lower but sharply drawn ribs bear at regularintervals, small humps ....... 32(31) The four ribs have no humps, sometimes the left rib is notdiscernible ......... 33(20) Seven to twelve transverse cirri 33a(33b) Seven, eight or nine transverse cirri and always in same propor-tion with 11, 13 or 15 ventral cirri . . . . 33b(33a) 10 to 12 transverse cirri but only seven ventral cirri . 34(15) On the left of the peristome, the left border bears a broad hori-zontal tooth. The following species (perhaps with nameA. dentata) form a distinct subgroup of the genus distinguishedby the five to seven relatively short broad transverse cirri in-serted obliquely, also the seven ventral cirri are conspicuouslybroad, frequently at the posterior of the ventral cirri stands aslender side-cirrus lying alongside the transverse ledge . 35(36) Small form, from a dorsal ridge, a thorn arches towards theposterior .......... 36(35) Dorsal without thorn 37(46) The anterior border has an obvious tooth and from there the leftside of the nucleus begins (cf. A. robustd) .... 38(43) Six transverse cirri, a side-cirrus at the posterior of the ventralcirri, a tooth-like projection at the anterior third on the leftborder, the right edge is very flat and transparent, in thefrontal group there are six to eight membranelles . 39(42) The posterior border has four to five teeth .... 40(41) The posterior has four or five sharply pointed teeth, dorsally arefour high ribs with sharp teeth ...... 41(40) The posterior teeth weakly developed, can also be distinct,dorsal ribs low, bear only humps ..... 42(39) The posterior border shows a tooth only on its left edge and isonly very weak in the remainder, dorsally are four variablyclear low ribs, often only the two middle one are stronglydeveloped 43(38) Five or seven transverse cirri . ...... 44(45) Five transverse cirri otherwise like the preceeding species . 45(44) Seven transverse cirri, the posterior edge either without distinctteeth or weekly notched 46(37) The front left edge forms no distinct tooth, on the left side of thebody is without distinct break or with a small indentation 47(50) Dorsal ridges weakly indicated 48(49) Large flat transparent species with three or four weakly indicatedridges, tooth on the left border exists strongly 49(48) Small slender form with a weak tooth on the left border .50(47) Four or six strong ribs dorsally 31 . 31A. tuber osa A. quadrilineata . 33a A. mutatisA. poly sty la . 35, A. dentata . 37 38 . 39. 40 A. pulcherrimaA. pulcherrima var baltica A. sedigita . 44 A. lyncaster A. crenata . 47. 48 A. leptaspisA. hexerls 51 32 I. C. H. WU & C. R. CURDS 51(52) Medium size form, with six to seven uniformly high and strong but round ribs ......... A. robusta 52(51) Very large form with two medial wing-like and two low lateral dorsal ribs ......... A. magna References Agamaliev, F. G. 1967. Faune des cilies mesopsammiques de la cote ouest de la Mer Caspienne. Cah,Biol. mar. 8 : 359-402 [English & Russian summary.] 1971. Complements to the fauna of psammophilic ciliates of the western coast of the Caspian Sea. Acta Protozool. 8 (30) : 379-404. [Russian : English summary.] 1974. Ciliates of the solid surface overgrowth of the Caspian Sea. Acta Protozool. 13 (5) : 53-82. [Russian : English summary.] 1975. A new species of ciliates (Hypotrichida) from the Caspian Sea. Zool. Zh. 54 : 1246-1248. Bick, H. 1972. Ciliated Protozoa. An illustrated guide to the species used as biological indicators in freshwater biology. Geneva (World Health Organisation). 198 pp. 94 figs.Bock, K. J. 1952. Uber einige holo- und Spirotriche Ciliaten aus den marinen Sandgebeiten der Kieler Bucht. Zool. Anz. 149 : 107-115. 1955. Condylostoma vastum nov. spec., und Aspidisca pertinens nov. spec., zwei sandbewohnende Ciliaten aus dem Kustengebiet der Kieler Bucht. Zool. Anz. 154 : 302-304. Borror, A. C. 1963. Morphology and ecology of the benthic ciliated protozoa of Alligator Harbor,Florida. Arch. Protistenk. 106 : 465-534. 1965. New and little-known tidal marsh ciliates. Trans. Am. microsc. Soc. 84 : 550-565. 1972. Revision of the order Hypotrichida (Ciliophora, Protozoa). J. Protozool. 19 (1) : 1-23. Bory, de St Vincent. 1827. Encyclopedic methodique. Histoire naturelle des zoophytes, ou animaux rayonnes, faisant suite a 1'histoire naturelle des vers de Bruguiere. Paris (Agasse, Imprimeur - Libraire). Livraison 98 (Tome 2, Pt 2) : 377-819.Brown, T. J. 1966. Observations on the morphology and reproduction of Aspidisca cicada Mtiller. N.Z. JlSci. 9(1): 65-76.1968. A reconsideration of the nomenclature and taxonomy of Aspidisca costata (Dujardin, 1842), (Ciliata). Acta Protozool. 5 (13) : 245-252.Buddenbrock, von W. 1920. Beobachtungen uber einige neue oder wenig bekannte marine Infusorien. Arch. Protistenk. 41 : 341-364.Burkovsky, I. V. 1970. The ciliates of the mesopsammon of the Kandalaksha Gulf (White Sea) I & II. Acta Protozool. 7 (33) : 475-489 & 8 (3) : 47-65. [Russian : English summary.]Claparede, E. & Lachmann, J. 1858. Etudes sur les infusoires et les rhizopodes. Mem. Inst. natn. genev. 5 : 1-260.Curds, C. R. 1975. A guide to the species of the genus Euplotes (Hypotrichida, Ciliatea). Bull. Br. Mus. not. Hist. (Zool.) 28 (1) : 1-61. 1977. Notes on the morphology and nomenclature of three members of the Euplotidae (Protozoa : Ciliatea). Bull. Br. Mus. not. Hist. (Zool.) 31 (6) : 267-278. Delphy, J. 1938. Etudes de morphologic et de physiologic sur la faune d'Arcachon. Bull. Stn. Biol. Arcachon 35 : 49-75.Deroux, G. & Tuffrau, M. 1965. Aspidisca orthopogon n. sp. Revision de certains mecanismes de la morphogenese a 1'aide d'une modification de la technique au protargol. Cah. Biol. mar. 6 : 293-310.Diller, W. F. 1975. Nuclear behaviour and morphogenetic changes in fission and conjugation of Aspidisca costata (Dujardin). /. Protozool. 22 : 221-229.Dini, F. & Bracchi, P. 1976. Ciclo cellulare di Aspidisca aculeata (Ehrenberg). Atti Accad. naz. Lincei Re. Ser. 8, Vol. LX (1) : 64-69.Dragesco, J. 1954. Diagnoses preliminaires de quelques cilies nouveaux des sables. Bull. Soc. zool. Fr. 79 : 62-70. 1960. Cilies mesopsammiques litteraux (systematique, morphologic, ecologie). Trav. Stn. biol. Roscoffl2(N.S.): 1-356. 1963. Complements a la connaisance des cilies mesopsammiques de Roscoff II. Heterotriches. HI. Hypotriches. Cah. Biol. mar. 4 : 251-275. 1965. Cilies mesopsammiques d'Afrique Noire. Cah. Biol. mar. 6 : 357-399. Dujardin, F. 1841. Histoire naturelle des zoophytes. Infusoires. Paris. THE GENUS ASPIDISCA 33 Ehrenberg, C. G. 1830 (1832). Beitrage zur Kenntniss der Organisation der Infusorien und ihrer geo-graphichen Vertreitung, besonders in Sibirien. Phys. Math. Abh. K. Akad. Wiss. Berlin 1830 : 1-88. 1838. Die Infusionsthierchen als vollkommene Organismen. Leipzig (L. Voss). 612 pp. Fabre-Domerque, P. 1885. Note sur les infusoires cilies de la baie de Concarneau. /. Anat. Physiol., Paris 21 : 554-568. Fresenius, G. 1865. Die Infusorien des Seewasseraquariums. Zool. Gart., Frankf. 6 : 81-89, 121-129.Fromentel, de E. 1874. Etudes sur les microzoaires ou infusoires proprement dits. Paris (Libraire de 1' Academic de Medicine).Gates, M. A. & Curds, C. R. 1979. The argyrome of the genus Euplotes (Hypotrichida, Ciliophora). Bull. Br. Mus. not. Hist. (Zool.) 35 (2): 127-1 34.Gelei, von J. 1939. Vollkommene Sinneselemente bei den hoheren Ciliaten II. Studie uber die Sinnesor- ganellen von Aspidisca - Arten: Allgemeines. Mat. termeszettud. Ert. 58 : 476-518.Ghosh, E. N. 1921. New hypotrichous infusoria from Calcutta. //. R. Microsc. Soc. 1921 : 248-250.Gourret, P. & Roeser, P. 1886. Les protozoaires du vieux-port de Marseille. Archs Zool. exp. gen. (2 e Serie) 4 : 443-534.Hamin, A. 1964. Untersuchungen iiber die Okologie und Variabilitat von Aspidisca costata (Hypotricha) im Belebtschlamm. Arch. Hydrobiol. 60 : 286-339.Kahl, A. 1928. Die Infusorien (Ciliata) der Oldesloer Salzwasserstellen. Arch. Hydrobiol. 19 : 50-123, 189-246. 1932. Urtiere oder Protozoa. I: Wimpertiere oder Ciliata (Infusoria), eine Bearbeitung der freile- benden und ectocommensalen Infusorien der Erde, unter Ausschluss der marinen Tintinnidae. In DahlF. [Editor] Die Tierwelt Deutschlands. Jena (G. Fischer): Teil 25 : 399-650. Klein, B. 1929. Weitere Beitrage zur Kenntnis des Silberliniensystems der Ciliaten. Arch. Protistenk. 65 : 183-257. 1958. The 'dry' silver method and its proper use. J. Protozool. 5 : 99-103. Madsen, H. 1931. Bemerkungen iiber einige entozoische und freilebende marine Infusorien der Gattungen Uronema, Cyclidium, Cristigera, Aspidisca und Entodiscus gen. nov. Zool. Anz. 96 : 99-112.Mansfeld, K. 1923. 16 neue oder wenig bekannte marine Infusorien. Arch. Protistenk. 46 : 97-140.Mereschkowsky, von C. 1878. Studien iiber Protozoen des nordlichen Russland. Arch, mikrosk. Anat. 16:153-248.Mtiller, O. F. 1773. Vermium Terrestrium et Fluviatilium seu Animalium Infusorium, Helminthicorum et Testaceorum, non Marinorum, Succincta Historia. Hauniae et Lipsiae. Vol. 1, 72 pp.- 1779. Zoologia danica seu animalium daniae et norvegiae rariorum ac minus notorum. Descriptiones et historia. Hauniae et Lipsiae. Volumen primum. (Plates published separately in 1777.) 1786. Animalcula Infusoria Fluviatilia et Marina. Hauniae. 367 pp. Penard, E. 1921. Etudes sur les infusoires d'eau douce. Geneve (Georg et Cie). 331 pp.Pereyaslawzewa, S. 1886. Protozoaires de la mer Noire. Zap. novoross. Obshch. Estest. 10 (II) : 79-114.Plough, H. H. 1916. The genus Aspidisca Ehrenberg. Trans. Am. Microsc. Soc. 35 : 233-244.Quennerstedt, A. 1867. Bidrag till Sveriges infusoriefauna II. Acta Univ. lund. 4 : 1-47. 1869. Bidrag till Sveriges infusoriefauna III. Acta Univ. lund. 6 : 1-35. Stein, F. 1 859. Der Organismus der Infusionsthiere nach eigenen Forschungen in systematischer Reihenfolge bearbeitet I. Leipzig. 206 pp.Summers, F. M. 1935. The division and reorganization of the macronuclei of Aspidisca lynceus Miiller, Diophrys appendiculata Stein and Stylonychia pustulata Ehrbg. Arch. Protistenk. 85 : 173-208.Tucolesco, J. 1962. Etudes protozoologiques sur les eaux roumaines. I. Especes nouvelles d'lnfusoires de la mer Noire et des Bassins sales Paramarins. Arch. Protistenk. 106 : 1-36.Tuffrau, M. 1964. La morphogenese de bipartition et les structures neuromotrices dans le genre Aspidisca (cilies hypotriches). Revue de quelques especes. Cah. Biol. mar. 5 : 173-199.Vacelet, E. 1961a. La fauna infusorienne des 'sables a amphioxus' des environs de Marseille. Bull. Inst. oceanogr. Monaco 3 (No. 1202) : 1-12. 19616. Les cilies de la microfaune des 'sables mal calbres' des environs de Marseille. Reel Trav. Stn mar. Endoume 36 (Bull, no. 22) : 13-19. Wallengren, H. 1900. Zur Kenntnis der vergleichenden Morphologic der hypotrichen Infusorien. Bik.K. svenska Vetensk. Akad. Handl. 26 (Afd IV, No. 2) : 1-31. 34 I. C. H. WU & C. R. CURDS Index of species and synonyms Aspidisca aculeata (Ehrenberg, 1838) Kahl, 1932 17 andreewi Mereschkowsky, 1878 . 19angulata Bock, 1952 . . 23 baltica Borror, 1965 . . 25 binucleata Kahl, 1932 . . 28caspica Agamaliev, 1967 . . 23cicada (Miiller, 1786) Claparede & Lachmann, 1858 . . 12costata (Dujardin, 1841) Stein, 1859 12 costata f. tetracirrata Tucolesco, 1962 12 crenata Fabre-Domerque, 1885 . 23dentata Kahl, 1928 . . .20fusca Kahl, 1928 . . .22fuscoides Agamaliev, 1975. . 23fjeldi Dragesco, 1960 . . 23glabra Kahl, 1928 . . . 16herbicola Kahl, 1932 . . \ihexeris Quennerstedt, 1 869 . 23hyalina Dragesco, 1954 . . jgirinae Burkovsky, 1970 . . 22leptaspis Fresenius, 1865 . . 23lyncaster (Muller, 1779) Stein, 1859 13 lynceus (Muller, 1773) Ehrenberg, 1830 . . .9magna Kahl, 1932 . . . 2 Qmajor (Madsen, 1931) Kahl, 1932 15major varfaurei Dragesco, 1960. 15marsupialis Penard, 1921 . \2maxima Vacelet, 1961 . . 20mutans Kahl, 1932 . . .27nana Tucolesco, 1962 . . 9orthopogon Deroux & Tuffrau, 1965 23 Aspidisca pelvis Delphy, 1938 . . .20per linens Bock, 1955 . . 23 plana Perejaslawzewa, 1886 . 15polypoda (Dujardin, 1841) Kahl, 1932 19 polystyla Stein, 1859 . . .15poly sty la var. maxima Gourret & Roeser, 1886 . . .19psammobiotica Burkovsky, 1970. 23pulcherrima Kahl, 1932 . . 25pulcherrima var. baltica Kahl, 1932 25 quadrilineata Kahl, 1932 . -19sedigita Quennerstedt, 1867 . 23steini Buddenbrock, 1920 . -16steini var. major (Madsen, 1931) Kahl, 1932 . . . .15sulcata Kahl, 1932 . . . 12tridentata Dragesco, 1963 . . 23tuberosa Kahl, 1932 . . . 19turrita (Ehrenberg, 1838) Claparede & Lachmann, 1858 nAspidiscopsis bengalensis Ghosh, 1921 . 12 Coccudina cicada Bory, 1827 . . -12 costata Dujardin, 1841 . . 19 crassa Dujardin, 1841 . -12 polypoda Dujardin, 1841 . . 19 Euplotes aculeata Ehrenberg, 1838 . . 17turritus Ehrenberg, 1838 . . \\ Kerona lyncaster Muller, 1786 . -13 Onychaspis aculeata Mansfeld, 1923 . 17 (Aspidisca) steini var. major Madsen, 1931 . . .15Oxytricha cicada Ehrenberg, 1 838 . . 19 Trichoda cicada Muller, 1786 . . -12lyncaster Muller, 1779 . .13lynceus Muller, 1773 ... 9 Related titles (Zoology series Vol. 36 No. 1)Published by the British Museum (Natural History) An Atlas of Freshwater Testate Amoebae By C. G. Ogden & R. H. Hedley 222 pp + 95 plates To be published Autumn 1979 The term 'testate amoebae' is given to those amoebid protozoa (Protozoa : Sarcodina :Rhizopodea) in which the cytoplasm is enclosed within a discrete shell or test, and whichextrude filose pseudopodia. Testate amoebae, also known as thecamoebae, are present in awide range of moist and freshwater habitats from moss, soil, peat, and standing water tosewage-treatment works. They are most commonly found in any moist situation wherethere are mosses, even occurring above ground level on the barks of trees and on the roofsof buildings. This handbook is intended as a field and laboratory guide to the commonBritish species. There are more than one hundred and fifty species recorded from the BritishIsles, of which about two-thirds are illustrated in this Atlas. Titles to be published in Volume 36 A guide to the species of the genus Aspidisca.By Irene C. H. Wu & C. R. Curds. The Hemiuroidea : terminology, systematics and evolution.By D. I. Gibson & R. A. Bray. Notes on the anatomy of Macrochirichthys macrochirusValenciennes, 1 844, with comments on the Cultrinae (Pisces,Cyprinidae). By G. J. Howes. Miscellanea Anatomy, relationships and classification of the familiesCitharinidae and Distichodontidae (Pisces, Characoidea).By R. P. Vari. Printed by Henry Lang Ltd, Dorchester Bulletin of the British Museum (Natural History) The Hemiuroidea: terminology,systematics and evolution D. I. Gibson & R. A. Bray Zoology series Vol 36 No 2 26 July 1979 The Bulletin of the British Museum (Natural History), instituted in 1949, is issued in fourSenUfic series, Botany, Entomology, Geology (incorporatmg Mineralogy) and Zoology,and an Historical series. Paoers in the Bulletin are primarily the results of research carried out on the unique andTver grow ng col ections of the Museum, both by the scientific staff of the Museum and byspeciS from elsewhere who make use of the Museum's resources. Many of the papers areworks of reference that will remain indispensable for years to come. Par are published at irregular intervals as they become ready, each is complete in itself,Sab e sepa ately and individually priced. Volumes contain about 300 pages and are notn^stril^mS within one calendar year. Subscriptions may be placed for one or moreerTes ^^Subscriptions vary according to the contents of the Volume and are based on a forecastS of tittsT each Volume nears completion, subscribers are informed of the cost of thenext Volume and invited to renew their subscriptions. Orders and enquiries should be sent to. Publication Sales, British Museum (Natural History),Cromwell Road, London SW7 5BD,England. World List abbreviation: Bull. Br. nat. Hist. (Zool.) Trustees of the British Museum (Natural History), 1979 mrw 1408 Zoology series Vol 36 No 2 pp 35-146 British Museum (Natural History) Issued 26 Ju] y 1979 London The Hemiuroidea : terminology, systematics andevolution David Ian Gibson and Rodney Alan Bray Zoology Department, British Museum (Natural History), Cromwell Road, London SW7 5BD Contents Synopsis 35 I. Introduction ............ 36 II. Definitions of hemiuroid structures with comments on their systematic value and possible function .......... 39 III. A classification of the Hemiuroidea with keys and definitions. ... 54 Introduction ............ 54 Hemiuroidea ............ 55 Accacoeliidae ........... 57 Azygiidae ............ 60 Bathycotylidae 62 Bunocotylidae 62 Derogenidae ............ 71 Dictysarcidae ........... 81 Hemiuridae ............ 84 Hirudinellidae ........... 98 Isoparorchiidae . . . . . . . . . . .100 Lecithasteridae . . . . . . . . . . .101 Ptychogonimidae . . . . . . . . . . .110 Sclerodistomidae . . . . . . . . . . .111 Sclerodistomoididae 114 Syncoeliidae 114 Generic index to part III. . . . . . . . . .116 IV. A discussion on the evolution of the Hemiuroidea. . . . . .118 Evolutionary trends in the Hemiuroidea . . . . . . .130 A suggested evolutionary scheme within the Hemiuroidea .... Some comments on the relationship of the Didymozooidea and the Paramphis- tomoidea to the Hemiuroidea 133 Acknowledgements 135 References . . . .135 Synopsis The history of the classification of the Hemiuroidea and the features which have been used as criteria fordistinguishing the higher taxa, such as adult morphology, life-cycle patterns and cercarial anatomy, arediscussed. It is suggested that the best basic criterion currently available is the functional morphology ofthe adult. Explanations of the terminology with comments on the systematic significance and possible functionof the features used in the study of hemiuroid taxonomy are included. A classification of the Hemiuroidea is presented with keys and definitions of the taxa to the genericlevel. The classification and definitions are based, where possible, on original observations of sectionedmaterial. The Hemiuroidea is divided into fourteen families. The Accacoeliidae contains the Accacoeliinaeand Paraccacladiinae, the latter subfamily consisting of only one genus. The Azygiidae consists of twosubfamilies, the Azygiinae and Leuceruthrinae. The Bathycotylidae, Isoparorchiidae and Ptychogonimidaecontain single genera, while the Hirudinellidae contains three monotypic genera. The Bunocotylidae is Bull. Br. Mus. not. Hist. (Zool.) 36 (2) : 35-146 Issued 26 July, 1979 36 D. I. GIBSON & R. A. BRAY redefined and contains the Bunocotylinae, Aphanurinae, Opisthadeninae (including Neotheletrum gen.nov.) and Theletrinae subfam. nov. The Derogenidae is also redefined and contains the Derogeninae,Gonocercinae and Halipeginae. The hemiuroids from the teleost swim-bladder, with the exception ofIsoparorchis, are placed in the Dictysarcidae, which is composed of the Dictysarcinae, Albulatrematinaeand Cylindrorchiinae subfam. inq. The Hemiuridae is restricted to ecsomate forms and contains thefollowing subfamilies: Hemiurinae, Dinurinae, Elytrophallinae, Glomericirrinae, Hypohepaticolinae,Lecithochiriinae, Lethadeninae, Plerurinae subfam. nov. and Pulmoverminae. The Lecithasteridae isredefined and is composed of the Lecithasterinae, Hysterolecithinae (including Thulinia gen. nov.),Macradeninae, Prolecithinae, Quadrifoliovariinae and Trifoliovariinae. The Sclerodistomidae containsthe Sclerodistominae, Prosogonotrematinae and Prosorchiinae. The Sclerodistomoididae fam. nov. iserected for Sclerodistomoides, and in the Syncoeliidae, the Syncoeliinae and Otiotrematinae are redefined.An index to the generic names used in this classification is included. The criteria which may be used as indicators of the relative 'primitiveness' of various taxa or to illus-trate phylogenetic relationships within the group are discussed. In relation to this, evolutionary trendswithin three organ-systems, (1) the seminal storage and disposal apparatus in the female reproductivesystem, (2) the vitellarium and (3) the terminal genitalia, are studied in detail. Using evidence from thisstudy, an evolutionary picture for the Hemiuroidea is presented, and its relationships with theDidymozooidea and the Paramphistomoidea are commented upon. I. Introduction The superfamily Hemiuroidea Looss, 1899, is a group within the Digenea which includes speciesusually parasitic in the gut, particularly in the stomach, of fishes. They are found predominantlyin marine teleosts, but also occur in freshwater teleosts, elasmobranchs and occasionally inamphibians and reptiles. It is not unusual for progenetic forms to occur in molluscs and othermarine, and occasionally freshwater, invertebrates. In addition to the alimentary canal of fishes,examples are known from the gall-bladder, swim-bladder, body-cavity, mouth, gills and fromthe skin, whilst all known species of one group are found in the lung of sea-snakes. Overall, thehemiuroids form a very diverse group, not only in habitat, but also in morphology. Indeed, thewide variations in adult morphology, even within proposed higher taxa, have resulted in a gooddeal of confusion with regard to the validity, composition and systematic relationships of thesetaxa. The superfamily was erected, under the name Hemiurida, by Dollfus (1923), and comprisedthe families Hemiuridae, Accacoeliidae and Syncoeliidae. Prior to this Looss (1907, 1908) hadcarefully re-described many species of hemiuroids and set a basic pattern on which later authors,notably Odhner (1911), Poche (1926) and Fuhrmann (1928), were able to build. These earlyworkers based their classifications entirely upon adult morphology and divided the group into asmall number of families, although not always indicating the relationships between these families.Odhner (1911), for example, grouped three families together, the Hemiuridae, Azygiidae andDidymozoidae. Since Odhner, the concept of the Hemiuridae has been sub-divided, condensedand sub-divided again on numerous occasions. Systematic histories of the Hemiuroidea havebeen compiled by Chauhan (1954), Skrjabin & Guschanskaja (1954, 1956, 1960) and morerecently by Stunkard (1973), although the latter author has omitted the important contributionsof Chauhan (1954), Manter & Pritchard (19600) and Mehra (1962). In order to avoid repetition,we have condensed several of the more recent conceptions of the Hemiuroidea in the form ofTable 1. It can be seen from this table that Odhner's original conception was split by Yamaguti(1971) into three superfamilies and eighteen families, one of which, the Hemiuridae, containstwenty-five subfamilies. The large number of higher taxa in this rather uncritical work of Yama-guti appears to be the result of the acceptance of inadequate descriptions as being accurate.Stunkard (1973) summarized the problem succinctly as follows: 'in the course of the past hundredyears, a large number of trematodes have been described, many on inadequate and erroneousinformation and based often on a single specimen. New genera and higher taxonomic categorieshave been erected to receive these dubious species.' Yamaguti, for example, has accepted threegenera in three different families for forms which we consider to be synonymous with the genusElongoparorchis Rao, 1961. Recent conceptions of the Hemiuroidea, and of the Digenea in general, have been greatly THE HEMIUROIDEA 37 38 D. I. GIBSON & R. A. BRAY influenced by the work of La Rue (1957), who sub-divided the Digenea into two groups, theEpitheliocystidia and the Anepitheliocystidia, depending upon the epithelial or membranousnature of the lining of the cercarial excretory vesicle. The Azygiidae was placed in the latter group,while the remainder of the hemiuroids with 'known' life-histories were placed in the former. Thiswork has resulted in the majority of recent workers considering the Azygiidae to be distinct fromthe Hemiuroidea, at least at the superfamily level (see Odening, 1974). Work by Powell (1972,1973, 1975) and Gibson (1974) indicated that it is likely that all cercariae have a syncytial liningto the excretory vesicle. This casts grave doubts upon the validity of La Rue's conceptions. Yamaguti (1971) stated that life-cycle patterns may be an important systematic feature; but,due to a lack of knowledge with regard to the life-histories of this group, this aspect appears tobe of little use in its classification. The little that is known suggests that, even within one family,the life-cycle can vary considerably in detail (see Chabaud & Buttner, 1959; Sinclair et al., 1973;Bray & Gibson, 1977). Stunkard (1973) gave a useful four-page summary of the present knowledgeof the hemiuroid life-cycle, and Yamaguti (1975) lists much of this information in more detail.Stunkard introduced his contribution as follows : The wide divergence of opinion concerningthe systematics and classification of the hemiuroid trematodes is the result, in large measures, oflack of knowledge of their life-cycles and developmental stages. Data are meager, fragmentary,often faulty, and sometimes erroneous.' He summarized his findings thus: 'The miracidia of thehemiuroid, azygiid and didymozoid species are unique and very similar. All are aciliate, providedwith an anterior circle of spines, and the surface of the body bears bristles . . . The cercariaedevelop in rediae; they lack penetration and cystogenous glands, and develop into the cysto-phorous stage which is characteristic for hemiurid trematodes. Typically they are eaten bycopepods and the metacercariae occur as unencysted larvae in the hemocoel of the crustaceans orother planktonic invertebrates that feed on copepods . . . The striking similarity of the larvalstages, and the fact that they are peculiar to the hemiurid trematodes, portends genetic homo-geneity and despite adult adaptations to different situations, the thesis of Odhner and Fiihrmannthat the Azygiidae, Hemiuridae and Didymozoidae are closely related is probably correct'. Weagree that these groups do seem to be closely related, although we are reluctant to place too muchemphasis on larval stages, especially considering the recent work of Devaraj (1972) and Schell(1975), who have described ciliated, non-spinous miracidia for the hemiuroids Isoparorchishypselobagri (Billet, 1898) and Lecithaster salmonis Yamaguti, 1934, respectively. Similarly, asmall number of cystophorus cercaria such as, Cercaria vaullegeardi Pelseneer, 1906, are knownto develop in daughter-sporocysts and not rediae (see Popiel, 1976). We are not convinced of theprimitive nature of the cercaria relative to the adult, because of the morphological similaritiesbetween what we consider to be primitive hemiuroids and the aspidogastreans (see below). Thehypothesis that the present adult digenean evolved from a mature, free-swimming cercaria-likeadult is presented by Cable (1965, 1974). It appears more likely to us that the adult forms fromvertebrates arose directly from primitive molluscan parasites, in much the same way as many aspi-dogastreans, and that the crustacean host and the cercarial stage are more recent developments.Pearson (1972) and Rohde (1972) discuss the two contrasting hypotheses concerning the evolu-tionary significance of the digenean life-cycle. It seems likely that the morphological differencesin cercariae, hitherto used as systematic indicators, are, at least to some extent, the result of theecological requirements of the life-history. If, for example, the crustacean host is benthic, thenthe cercarial tail will tend to be of a different shape to that of a species which has a pelagic crusta-cean host. In other superfamilies, such as the Allocreadioidea, there appear to be major differencesin the cercariae of different families. A similar argument also applies when considering thechaetotaxy of cercariae as a systematic criterion. In the latter case there is no reason why thehypertrophy or atrophy of the nervous system does not depend upon the ecological requirementsof the life-history. One additional disadvantage in using larval characteristics or life-history forsystematic purposes, is that for the majority of determinations only adult-specimens are availablefor study. The lack of knowledge with regard to the larval stages and life-histories of the greatmajority of genera, however, remains the greatest limitation to their value in systematics. Wesuggest, therefore, that the use of life-history details, and particularly cercarial morphology,should be treated with at least as much caution as the use of adult morphology. THE HEMIUROIDEA 39 We consider that neither the gross morphology of the adult, due to its variability, nor the useof life-cycle patterns and cercarial morphology, due to a lack of knowledge and understanding withregard to their significance, are able to provide us with a satisfactory classification. In our opinion,functional morphology appears to offer the best alternative. In order to use this concept, one musthave a detailed knowledge of the morphology of an organ or organ-system and an understandingof its probable function. Once its function is understood, one can then comprehend the require-ments for such an organ in order that the animal might complete its life-history. With an under-standing of the function and requirement for particular organs and organ-systems, one canrationalize many of the diverse variations which occur in different taxa, and recognize wheredevelopment or atrophy has occurred. This sheds light, not only upon the systematics, but alsoupon the phylogenetic relationships of the taxa. It also tends to expose inaccurate descriptionsand is a useful aid in suggesting the probable structure of particular organs in inadequately des-cribed taxa. The following classification, which we propose for the Hemiuroidea, is based,therefore, upon adult morphology associated with an attempted understanding of the functionof organs and organ-systems. This functional aspect has permitted us to try and base our con-cepts upon a combination of features, rather than upon one critical feature. II. Definitions of hemiuroid structures* with commentson their systematic value and possible function Accessory excretory organ (vesicle) - see Manter' s organ.Annulations or annular plications - see plications. Blind seminal receptacle - a type of seminal receptacle which does not communicate with theexterior via Laurer's canal, but which is linked to the oviduct by a short duct (Fig. 1) and usuallyhas a thick wall. It serves as a seminal store, and its presence, except in the cases in the Tri-foliovariinae and Derogeninae where it appears to have arisen from a canalicular seminal recepta-cle by the loss of Laurer's canal, appears to be a good systematic feature at the subfamily level.It is worth noting that when a blind seminal receptacle is present, the uterine seminal receptacle(q.v.) is lost. See seminal receptacle. Canalicular seminal receptacle - a large proximal dilation of Laurer's canal which is normallyfilled with fresh, as opposed to spent, spermatozoa (Fig. 1). This type of seminal receptacle (q.v.)in the majority of cases is possibly a recent adaptation associated with the use of Laurer's canalas a vagina (Gibson & Bray, 1975). See seminal receptacle. Cirrus - an intromittent copulatory organ which is formed from or encloses the male duct only.It is rare in hemiuroids, occurring only in the members of the Hirudinellidae. Although itspresence in certain other hemiuroid groups has been indicated in the literature, in two such cases,the hemiurid Glomericirrus and the derogenid Arnola, our observations of sectioned materialshow that this structure is definitely absent, there being a sinus-organ (q.v.) present. The occur-rence of a cirrus in the Hemiuroidea, therefore, is most likely a feature of importance at the familylevel. It is unlikely, however, that the 'cirrus' of the hirudinellids is homologous with the cirruscommon in many groups of Digenea. Cirrus sac - a muscular sac which surrounds the terminal portion of the male duct including thecirrus. Its function appears to aid the eversion of the cirrus (q.v.) and the expulsion of sperma-tozoa, as it often encloses the seminal vesicle (q.v.), during copulation by exerting hydrostaticpressure upon its contents. It is to some extent, therefore, analogous with the sinus-sac (q.v.).This structure occurs in the Hirudinellidae: its reported presence in other hemiuroid groups,such as the Halipeginae, we consider to be extremely doubtful. The presence of a cirrus-sac is inour opinion a feature of importance at the family level in the Hemiuroidea. * It should be noted that a smaller glossary of terms used in hemiuroid systematics was produced by Manter (1970).There are, however, significant differences between some of our definitions and those of Manter. usr Fig. 1. The different types of seminal receptacle present in the Hemiuroidea: A. Uterine seminalreceptacle; B. Rudimentary seminal receptacle; C. Canalicular seminal receptacle; D. Blindseminal receptacle, [bsr, blind seminal receptacle; csr, canalicular seminal receptacle; Lc, Laurer'scanal; rsr, rudimentary seminal receptacle; usr, uterine seminal receptacle.] THE HEMIUROIDEA 41 Cyclocoel - the name given to the gut-caeca when fused terminally, thus forming a completecaecal ring. The advantage of this caecal arrangement is unknown. This feature is of generic im-portance only, as it occurs widely in unrelated groups both within and outside the Hemiuroidea.The apparent cyclocoel found in large specimens of Hirudinella appears to be a subterminal fusionof the gut-caeca which takes place during the development of the animal.' DrUsenmageri 1 - this structure, the name of which means 'glandular stomach', is found at the'shoulder'-region of the gut-caeca in many hemiuroids. It is usually an expanded region lined bylarge, glandular cells forming a villous luminal surface, which is readily distinguished from thelining of the remainder of the caecum. Its function is not known, but it is probably a region ofspecialized secretion and/or digestion. It does not appear to be of systematic significance as itoccurs widely in distantly related hemiuroids, but it is apparently absent in the azygiids. Manter(1970) refers to these structures as 'precaecal sacs'. Ecsoma - this is the name given to the posterior region of the body of an adult digenean, when itis capable of being retracted within the body (soma). This structure, which appears to be uniqueto the Hemiuridae, is occasionally referred to as a 'tail' or the specimens are referred to as'appendiculate' or 'ecsomate'. The gut-caeca, uterus and, on rare occasions, the ovary and vitel-larium may extend into the ecsoma, and the excretory pore opens terminally on it. The mechanismof extension is not known, although the body-wall clearly contains longitudinal and circularmuscles; but within the ecsoma are numerous large, vesicular cells which might be involved withthis process, acting as a hydrostatic skeleton. Its function is thought to be that of a feeding organwhich is extruded during periods when the pH or the osmolarity of the stomach contents is at atolerable level. It should be noted that hemiurids tend to occur in the lumen of the stomach,especially the pyloric region, of marine teleosts and are, therefore, subject to great variations inpH and osmolarity (MacKenzie & Gibson, 1970). We suggest that other groups present in thestomach of these fish, such as the derogenines, tend to live more in the cardiac end of the stomachand only migrate down into the lumen during periods of more neutral pH and/or low osmolarity.These suggestions are made on the basis of observations of Derogenes varicus and Hemiuruscommunis. In relation to this function, the development of the ecsoma appears to be associatedwith the development of plications (q.v.) of the tegument. As the ecsoma occurs only in the hemiurids, this feature is of importance at the family level. Insome groups, however, such as in some of the lecithochiriine genera, the ecsoma may be reducedin size. Egg-filaments - in a few hemiuroids the egg-shell may be drawn out at the poles to form filaments.Usually, these are unipolar and may be of variable length. Occasionally, they are bipolar and maybear more than one filament (e.g. Anguillotrema). It is likely that these filaments are part of amechanism associated with the acquisition of the first intermediate host. They may, for example,become attached to the gill-filaments of the mollusc. In the case of Hypohepaticola, which tendsto be a tissue-parasite, the spine-like filament may aid the exit of the egg from the tissue by amechanism similar to that found in schistosomes. The presence of egg-filaments is a feature ofonly generic importance, as it occurs spasmodically throughout the group, particularly in theDerogenidae. Ejaculatory duct - the entire male duct distal to the seminal vesicle can theoretically be referredto as the ejaculatory duct. Regions such as the pars prostatica (q.v.) and cirrus (q.v.) are modi-fications of the ejaculatory duct. In the hemiuroids, however, the region generally referred to asthe ejaculatory duct is an unmodified region of this duct and is, therefore, without an alternativename. When present, it occurs between the pars prostatica and the hermaphroditic duct (q.v.) [orterminus of the male system]. It may occur entirely or partly inside or outside the sinus-sac (q.v.).This region of the duct is of little systematic importance, except perhaps at the specific level ; butit is long in certain lecithasterids, especially in the Macradenininae. Occasionally, unmodifiedregions of the male duct occur between the seminal vesicle and the pars prostatica or separatingtwo regions of the pars prostatica. These regions, however, are not referred to as the ejaculatoryduct, but usually as tubular extensions of the seminal vesicle or aglandular regions of the parsprostatica. 42 D. I. GIBSON & R. A. BRAY Ejaculatory vesicle - a dilation of the ejaculatory duct (q.v.) within the sinus-sac (q.v.). Thisfeature occurs in certain lecithochiriine genera and, in its glandular form (see prostatic vesicle),in the Glomericirrinae, Hysterolecithinae and the remainder of the lecithochiriines. It appearsto function as a small seminal reservoir as part of a mechanism to increase the amount of sperma-tozoa ejected from the sinus-sac during copulation. Nasir & Diaz (1971) suggest that an ejacula-tory vesicle is merely a prostatic vesicle from which the cellular lining has been lost, hence wesuggest that it might be more appropriate to refer to the prostatic vesicle as a 'glandular ejacula-tory vesicle' (see p. 93). The presence of an ejaculatory vesicle or a glandular ejaculatory vesicle(prostatic vesicle) is a feature of importance at the subfamily level. Excretory vesicle (bladder) - in hemiuroids this is essentially Y-shaped, the arms often unitingdorsally to the pharynx or oral sucker. The presence of blind arms is a feature of no more thangeneric importance, as it appears to occur widely in distantly related forms, and indeed we havenot used it at the generic level in the case of the azygiid genus Otodistomum. There are a numberof modifications of the basic structure of this organ, especially in the stouter hemiuroids. Theseinclude: (1) in the Sclerodistomidae there are one or two Manter's organs (q.v.), often called'accessory excretory vesicles', which communicate with this organ distally; (2) in Hirudinella,Botulus and Sclerodistomum the arms form a branching system of tubules or diverticula; (3) insome of the primitive groups, such as the Accacoeliidae, Hirudinellidae and Syncoeliidae, theexcretory arms are usually arranged so that initially they pass forward dorsally and ventrally^instead of laterally ; and (4) in the Ptychogonimidae the excretory arms unite twice in the forebody Fischthars organ - this is a name given by Yamaguti (1971) for a round vesicle of unknownfunction, lined with epithelial cells and surrounded by a dense mass of gland-cells, which appar-ently opens dorsally to the right of Mehlis' gland (q.v.) in Pelorohelmins palawanensis Fischthal &Kuntz, 1964. There is no evidence of such a structure in specimens under the name of P. ghanensisFischthal & Thomas, 1968, from the collection of the British Museum (Natural History). It ispossible, therefore, that Yamaguti may have mistaken Juel's organ (q.v.) for this structure. Healso, however, describes this structure in Meristocotyle varani Fischthal & Kuntz, 1964, a speciesof unknown relationship; but in this case it is the distal dilation of Laurer's canal which opensdorsally. [We should point out that we regard Pelorohelmins to be a synonym of Elongoparorchis.] Genital atrium - a receptacle present in most hemiuroids between the hermaphroditic duct andthe genital pore, which probably acts as a vagina during copulation. Spermatozoa are probablydeposited within this structure by the copulatory organ of another worm when cross-inseminationoccurs, and it is then either sucked back into the hermaphroditic duct by the action of the sinus-sac or, more likely, forced back (the sinus-organ being retracted to receive it) by the action of themuscular walls of the genital atrium which are contractile. The lining of the genital atrium iscontinuous with the sinus-organ (or in the case of the hirudinellids, the 'cirrus'), and appears tocontribute significantly to the formation of its outer surface as it extends. In some of the hirudinel-lids the genital atrium may be everted through the genital pore, thus giving extra length to the'cirrus' (see Fig. 12D of Gibson & Bray, 1977). This also occurs in Isoparorchis (Fig. 2), where itadds additional length to the sinus-organ. The contractile nature of this organ makes it of limited taxonomic value, even at the specificlevel, although its apparent total absence may be of some value. It is often reduced or absent inspecies which must rely upon self-insemination or which possess only a temporary sinus-organ.When the sinus-organ and sinus-sac are absent, it is difficult to distinguish the genital atrium fromthe hermaphroditic duct. In such cases, these two terms often appear to have been used inter-changeably. Genital pore - the aperture through which the contents of the genital ducts pass to the exterior.It usually, in the Hemiuroidea, forms the mouth of the genital atrium, but occasionally occurs atthe distal end of the hermaphroditic duct, when the genital atrium (q.v.) is absent, or at the unionof the male and female ducts when both the hermaphroditic duct and the genital atrium areabsent. The genital pore is not always the most distal part of the terminal genital apparatus, asduring copulation the copulatory organ, or even the genital atrium, is thrust through the genital THE HEMIUROIDEA 43 Fig. 2 Sagittal sections through the terminal genitalia of Isoparorchis : A. Withdrawn; B. Extruded,[so, sinus-organ; wga, wall of genital atrium.] 44 D. I. GIBSON & R. A. BRAY pore. This structure is of little systematic importance as it occurs mid-ventrally in the anteriorforebody in all hemiuroids. Hermaphroditic duct - a duct commonly linking the terminal male and female ducts with thegenital atrium. The duct itself appears to have arisen partly as a modification of the genital atriumand partly from the fusion of the male and female ducts. It is normally quite distinct from thegenital atrium; but, in certain cases, when the sinus-sac and sinus-organ are absent, it is difficultto distinguish these structures. An hermaphroditic duct occurs in most hemiuroids, commonlywithin the sinus-sac and almost always within the sinus-organ, when the latter structure ispresent. Annular muscles are sometimes clearly seen in its walls, e.g. Elytrophalloides, andprobably serve to transport eggs and spermatozoa along its length by peristalsis. In some genera,such as Paradinurus and Hemiurus, the proximal part of the hermaphroditic duct is lined byvillous, glandular cells of unknown function: this region may serve a similar function to theprostatic vesicle (q.v.) of the lecithochiriines. The distal part of the hermaphroditic duct inHemiurus is lined with cuticular papillate structures: as this is the region which forms the outersurface of the temporary sinus-organ, it presumably aids the maintenance of the union duringcopulation. There are indications in Halipegus that the hermaphroditic duct in some species ofthis genus may be transitory, developing from the sinus-organ as it extends. The absence of an hermaphroditic duct, except in the case of the Hirudinellidae and in Halipegus,is of generic importance only, because of: (1) the inability to distinguish it in some cases fromthe genital atrium ; and (2) the fact that degeneration of the terminal genitalia, due to the increa-sing importance of self-insemination, appears to have occurred independently on a number ofoccasions. Hermaphroditic sac - see sinus sac. Inner vesicle- this is the name given by Juel (1889) to the sac-like structure (Fig. 3), filled withactive and/or disintegrating spermatozoa found within the structure which we have called Juel'sorgan (q.v.). In the rudimentary form of Juel's organ (see rudimentary Juel's organ) this sac-likestructure has not been enveloped, and is referred to here as a 'rudimentary seminal receptacle'(q.v.). According to Juel (1889) and Lander (1904), the inner vesicle normally appears to have anaperture at its distal end, and presumably it is through this that the disintegrating spermatozoaand vitelline material pass into the outer, amorphous mass of Juel's organ. The inner vesicle,which may be oval or in the form of a convoluted tube, appears to act, therefore, as a 'killingchamber' for the excess reproductive material. This structure is present in all of the groups where a fully developed Juel's organ occurs, andits taxonomic significance is as discussed for the latter organ. It should be noted that in the caseof certain didymozooids the inner vesicle does not appear to be entirely enveloped by the outermass of Juel's organ. JueVs organ - in many hemiuroids, and all hemiurids, Laurer's canal does not open dorsally,but leads into an organ which has been referred to as a 'seminal receptacle' or, more recently 'thepouch of Laurer's canal' (Madhavi & Rao, 1974). It was apparently first described by Juel (1889),and we, therefore, felt (Gibson & Bray, 1975) that Juel's organ was an appropriate designation.It consists of an oval or globular sac containing an amorphous granular material, with theoccasional (?) amoeboid cells embedded in it (Figs 3 A & 4A). An 'inner vesicle' (q.v.), eitherglobular and/or tubular, lies within this mass and contains spent (but often active) or partlydisintegrated spermatozoa, vitelline material and, occasionally, ova. The inner vesicle is fed byLaurer's canal, which may be long or short, depending upon the proximity of Juel's organ toMehlis' gland. The other end of the inner vesicle opens into the outer mass of Juel's organ.Sometimes Juel's organ and Mehlis' gland are apparently enclosed by a common membranoussheath, but in other species Juel's organ lies outside the sheath surrounding Mehlis' gland. The function of Juel's organ is, apparently, as a disposal unit for excess reproductive material,which enables these resources to be recycled and is thus economically advantageous to the wormcompared with the situation where Laurer's canal acts as a drain for these products. It is possible Jo B Fig. 3 Diagrammatic representation of a fully developed (A) and a rudimentary (B) Juel's organ,[iv, 'inner vesicle'; Jo, Juel's organ; Lc, Laurer's canal; rJo, rudimentary Juel's organ; rsr,rudimentary seminal receotacle: usr. uterine seminal receptacle.! 46 D. I. GIBSON & R. A. BRAY that the (?) amoeboid cells in the outer mass of Juel's organ might be involved in the final break-down of this waste material. A fully developed Juel's organ is found in all hemiurids (sensustricto), the aphanurine bunocotylids, the dictysarcids, the hysterolecithine lecithasterids and insome halipegine derogenid genera. It also occurs, in a slightly modified form, in the nemato-bothriine didymozooids. In certain derogenine and sclerodistomid genera Juel's organ possesses no inner vesicle. Thisform, which we consider to be more primitive, we have referred to as a 'rudimentary Juel'sorgan' (q.v.). In this case there is usually a rudimentary seminal receptacle (q.v.), from whichthe 'inner vesicle' is later formed, that leads via a region of Laurer's canal of varying length intoan amorphous mass, resembling the outer region of the fully developed Juel's organ (Figs 3B &4B). The presence of a fully developed Juel's organ we consider to be a feature of significance atthe subfamily level, except in the case of the Halipeginae, where it is of generic importanceonly (but see Genarchopsis). Laurer's canal -a. duct which links the oviduct with either the exterior, a seminal receptacle (q.v.)or with Juel's organ (q.v.). Its function has long been a matter of contention. Looss (1893) wrotea paper entitled, '1st der Laurers'che Kanal der Trematoden eine Vagina?' and he, Goto (1893)and Johnston (1912) believed that it functioned as a 'sperm-drain'. Cohn (1902, 1903) andPalombi (1931), however, have described examples where Laurer's canal is used as a vagina. Thiswork led Hyman (1951) to state, 'Laurer's canal in flukes was formerly considered to serve as anexit for superfluous sperm and yolk cells but is now known to function in copulation'. Our recentwork (Gibson & Bray, 1975) with hemiuroids has indicated that Laurer's canal does in factfunction in this group as a drain for excess and/or spent seminal and vitelline material, and wesuggest that in other groups the use of this canal as a vagina during copulation is a more recentdevelopment associated with the loss of a uterine seminal receptacle (q.v.) and the developmentof a functional seminal receptacle as a proximal dilation of this canal, i.e. a canalicular seminalreceptacle (q.v.). It should be noted that Juel's organ appears to be a modification of Laurer'scanal. The nature of Laurer's canal and its presence or absence are often useful features at thesubfamily or family level, except in the cases of the Derogeninae, Halipeginae, Prosorchiinae andTrifoliovariinae. Manner's organ (accessory excretory organ or vesicle) - a tubular vesicle lined with an epitheliumand usually surrounded by bundles of muscle, especially longitudinal muscle. It occurs dorsal tothe excretory vesicle (q.v.) into which it opens postero-ventrally close to the excretory pore. Itis a feature of the Scerodistomidae, occurring singly in Prosogonotrema, Prosorchis andProsorchiopsis and paired in Sclerodistomum. Gibson & Bray (1977) suggest that it might occurin Distoma gigas Nardo, 1827, a giant digenean of uncertain systematic position. The nameManter's organ appears to have been coined by Yamaguti (1971), and is in our opinion moreacceptable than the appellation 'accessory excretory organ (vesicle)', as the function of this organis unknown. Mehlis' gland- a cluster of gland-cells which surround the region of the ovovitelline canal whichlinks the oviduct and the uterus: this is usually the region of the ootype (q.v.). It is thought toproduce a mucous secretion which lubricates the uterus and a lipoprotein secretion which formsa membrane around the ovum and vitelline cells upon which shell-material is then deposited(Smyth, 1966). It also seems likely that it may produce a secretion which activates the spermatozoa.Mehlis' gland appears to be of little systematic importance, except that, although in themajority of hemiuroids it is post-ovarian [the oviduct leaves the ovary posteriorly], in the azygiidsand accacoeliine accacoeliids it is pre-ovarian [the oviduct leaves the ovary anteriorly]. It islikely that there are several exceptions to this rule, such as the prosorchiine sclerodistomids. Incertain hemiuroids Mehlis' gland appears to be enclosed along with Juel's organ by a membranoussac (see Madhavi & Rao, 1974). Melralerm - a name given to the terminal region of the uterus, when it can be distinguishedmorphologically from the rest of this organ. It is of little taxonomic importance in this group, asit is usually difficult to distinguish and often tends to grade into the uterus-proper. It is usually THE HEMIUROIDEA 47 rs rsrLc rJo 01 33 Fig. 4 Sections of a fully developed (A) and a rudimentary (B) Juel's organ, [gc, gut-caeca; iv, innervesicle; Jo, Juel's organ; Lc, Laurer's canal; Mg, Mehlis' gland; o, ovary; rJo, rudimentary Juel'sorgan; rs, ventral sucker; rsr, rudimentary seminal receptacle; u, uterus; usr, uterine seminalreceptacle; v, vitellarium]. 48 D. I. GIBSON & R. A. BRAY muscular, often surrounded by small gland-cells and in some dinurines it has a villous lining.In Erilepturus (= Uterovesiculurus) it appears to form a distinct dilate sac. Ootype - a region of the female duct (ovovitelline canal) where egg-formation and possiblyfertilization occur. This is normally the region, surrounded by Mehlis' gland (q.v.), which linksthe oviduct with the uterus. In the hemiuroids this region does not appear to be vesicular as inmany other digeneans, but is present as a narrow tube. Although we have seen soft egg-shells inthis region in Isoparorchis, Otodistomum and some hemiurids, in othe'rs, such as Derogenes,Pulmovermis and Syncoelium, the ootype appears to extend into the first part of the uterus, asegg-shell formation occurs in a region not surrounded by Mehlis' gland. We are referring to thisregion as a uterine ootype (q.v.). The systematic significance of these variations of the ootype havenot been studied ; but it seems unlikely that they may be of any value above, perhaps, the genericlevel. Ovary - in the hemiuroids this is usually oval in shape, but in certain groups, such as the lecithas-terids, syncoeliids and dictysarcids, it is commonly composed of 4 or 5 distinct lobes. In one instance(Isoparorchis) the ovary is tubular. The position of the ovary in relation to the testes is an impor-tant systematic criterion at the subfamily level, except in the case of some of the macrodenininelecithasterids. The ovary is post-testicular in most groups, but is pre-testicular in the azygiineazygiids, the ptychogonimids, the gonocercine derogenids and certain macradeninine lecithasteridgenera, and occurs between the testes in the bathycotylids. The ovary occurs in the hindbody inall groups, except for the prosogonotrematine sclerodistomids. Oviduct - the duct linking the ovary and the ootype (q.v.). It receives Laurer's canal and thecommon vitelline duct before, or sometimes in the case of the common vitelline duct, slightlyafter entering Mehlis' gland (q.v.). The oviduct appears to leave the ovary posteriorly in themajority of hemiuroids, the exceptions being the azygiids, the accacoeliine accacoeliids andpossibly odd genera, such as Prosorchiopsis, in other groups. Pars prostatica - the region of the male duct between the seminal vesicle and either the ejaculatoryduct or the hermaphroditic duct. It is normally surrounded by prostatic gland-cells and lined bywhat appear to be anuclear gland-cells which often project into the lumen presenting a papillateor villous appearance: it is possible, however, that the latter are merely internal extensions ofthe outer gland-cells. The function of this region is not known for certain, but it may produce asecretion which protects and lubricates the spermatozoa during ejaculation. It may also be in-volved in the activation of spermatozoa during ejaculation. The shape of this duct, i.e. whether itis vesicular or tubular, is of specific value, and so is its length. The presence of a vesicular parsprostatica has often been confused with a prostatic vesicle (q.v.). When the external gland-cellsare severely restricted in their distribution by surrounding parenchyma or are bound by a fibrousmembrane, they are spoken of as being 'delimited'. In certain cases an aglandular duct links thepars prostatica and the seminal vesicle; this is usually referred to as a tubular extension of theseminal vesicle or as an aglandular region of the pars prostatica. An aglandular region also linksthe two parts of the pars prostatica in the dinurine hemiurid Mecoderus. Peduncle - this is a stalk upon which the ventral sucker may be surmounted. It occurs only in afew species of hemiuroids. It may be of some taxonomic importance at the generic level ; but it isoften variable in size, sometimes being either difficult to distinguish or prominent in the samespecies, e.g. in Accacladium serpentulum Odhner, 1928, as described by Bray & Gibson (1977). Permanent sinus-organ - see sinus-organ (permanent). Plications - regular backwardly directed thickenings of the tegument which surround or partlysurround the body transversely. They are a feature unique to the hemiurids and the aphanurinebunocotylids; but only occur in certain genera, being a feature normally considered to be ofsystematic importance at the generic level (a notable exception being the genus Aphanurus, butsee p. 65). They may occur over the whole body (soma) or just part of it, and tend to be betterdeveloped anteriorly than posteriorly, especially in the dorsal field. They are never present on the THE HEMIUROIDEA 49 ecsoma. Care should be taken not to confuse these regular tegumental thickenings with a rugateappearance caused by contraction, with small transverse ridges caused by circular muscles inthe body-wall of poorly preserved material (these do occur on the ecsoma), and with transversefolds of the body-wall surrounding the suckers of certain bunocotylid genera. Plications appear to be a primitive hemiurid feature which arose in association with theecsoma (q.v.). They are possibly a feature which permits the thickening of the somatic tegumentduring periods of low pH or high osmolarity when the ecsoma is withdrawn, and yet still allowsfull and easy extension and contraction of the body during periods of activity. Certain genera,which possibly no longer inhabit the pyloric region of the stomach or which are parasitic inphysiologically 'stomachless' fish (see Barrington, 1957), have lost this feature. Pre-acetabular pit - see presomatic pit.Precaecal sac - see ' Driisenmagerf '. Pre-oral lobe - a small region of the body anterior to the oral sucker. In some instances it mayactually overhang the anterior margin of the oral sucker. It has no apparent systematic impor-tance, except that it is glandular in one species of Otodistomum (see Gibson & Bray, 1977), as itappears to occur, at least to some extent, in all hemiuroids. Presomatic pit (preacetabular pit) - a deep, concave depression, circular or oval in section, whichis present mid-ventrally just anterior to the ventral sucker. It occurs in certain lecithochiriinegenera, in the plerurine genus Synaptobothrium and apparently in the aphanurine genusMitrostoma. Great care should be taken in its use as a taxonomic criterion as it is easily confusedwith the ventro-cervical groove (q.v.), which is common in many hemiurids. In the genusLecithochirium this structure can be either present or absent, being very small and difficult todistinguish in the type-species: this does not appear, therefore, to be a useful character in dis-tinguishing Lecithochirium and Sterrhurus (see p. 93). The presomatic pit often has a region of glandular tissue around its base ; but its actual func-tion is not understood. Lloyd (1938) has suggested that it acts as a chemo-sensory organ and thatit may be associated with the extrusion and withdrawal of the ecsoma : it would appear that thelatter certainly cannot be the case in Mitrostoma. Prostatic sac -a term coined by Gibson (1976) for the muscular sac which surrounds the parsprostatica and the seminal vesicle of the azygiids. Its function is not known for certain, butpresumably it aids the evacuation of spermatozoa and prostatic secretion during ejaculation. Prostatic vesicle - a dilation of the ejaculatory duct within the sinus-sac, which is usually lined byglandular cells and occurs in addition to an external pars prostatica. Essentially, it is identical toan ejaculatory vesicle (q.v.), except for the presence of the glandular cells. As the latter cells canapparently be lost, it does seem unwise to distinguish a prostatic vesicle from an ejaculatoryvesicle, and, in view of the possibility of confusing the former structure, both nomenclaturallyand morphologically, with a 'vesicular pars prostatica' (q.v.), it might be advisable to refer to theprostatic vesicle as being a 'glandular ejaculatory vesicle'. This structure occurs for certain onlyin the lecithochiriine, glomericirrine and hypohepaticoline genera, and is possibly a feature ofimportance at the subfamily level (if included as a type of ejaculatory vesicle). We do not considerthat this structure occurs in any of the plerurine or pulmovermine genera, for in these cases thepars prostatica itself appears to be partly enclosed by the sinus-sac in cases when the latter ispresent. The function of a prostatic vesicle is probably identical to that suggested for an ejacula-tory vesicle. Receptaculum seminis - see seminal receptacle. Receptaculum seminis uterinum - see uterine seminal receptacle. Rudimentary Juel's organ - a form of Juel's organ (q.v.) which lacks an 'inner vesicle' (q.v.). Ithas a granular appearance and is present usually at the distal end (Figs 3B & 4B), but occasionallymore proximally, of Laurer's canal. It presumably has a similar function to a fully developedJuel's organ, into which it has probably evolved in more advanced forms by enveloping the 50 D. I. GIBSON & R. A. BRAY rudimentary seminal receptacle (q.v.) and forming an 'inner vesicle'. Small, black structures canbe seen within the amorphous mass which fills this organ: we wonder whether these might bebacteria which may carry out the final breakdown of the excess seminal and vitelline material,much as we suggest that (?) amoeboid cells might do in a fully developed Juel's organ. A rudimentary Juel's organ is known to occur in certain derogenine derogenid and prosogono-trematine and prosorchiine sclerodistomid genera, but its taxonomic significance, even at thegeneric level, is uncertain. This organ also appears to occur in the aspidogastrean Aspidogasterconchicola von Baer, 1826 (see p. 123). Scales -a term used by Manter (1934) to describe the structures on the tegument of Dinosoma.We believe that they are probably just regularly crenulate plications (q.v.). Seminal receptacle - a general term covering several different types of apparatus for the storageof spermatozoa in the female reproductive system. In our opinion the various forms of seminalreceptacle should be clearly differentiated in descriptions, as they are important taxonomiccriteria. We recognize four different kinds of seminal receptacle present in the Hemiuroidea(Fig. 1): (1) a 'blind seminal receptacle' (q.v.), which is a blind sac, linked to the oviduct by ashort tube, occurring in most of the lecithasterid subfamilies, the opisthadenine bunocotylids andthe derogenid genus Leurodera, and which appears to have evolved from Juel's organ (q.v.) orin some cases from a rudimentary or canalicular seminal receptacle; (2) a 'canalicular seminalreceptacle' (q.v.), which is a large proximal dilation of Laurer's canal, and occurs frequently inother groups of digeneans, but apparently within the Hemiuroidea it occurs for certain only inthe lecithasterid genus Trifoliovarium and in a modified form in the derogenid genus Progonus;(3) a 'rudimentary seminal receptacle' (q.v.), which is a small proximal dilation of Laurer's canalthat, when present, always occurs together with a uterine seminal receptacle, but this form differsfrom the others in that it is not a store of fresh, quiescent spermatozoa and in that the smallamount of spermatozoa which it does contain are spent, although often still active; and (4) a'uterine seminal receptacle' (q.v.), which is a store of spermatozoa present in the proximal regionof the uterus, and occurs in the majority of hemiuroids. Another type is an 'oviducal seminalreceptacle', which is formed as a dilation of the oviduct; but this type does not occur in theHemiuroidea. With the exception the 'rudimentary' and 'uterine' types, the various forms ofseminal receptacle do not normally occur together in the same individual. Seminal sac - a term used by Manter (1947) for an oval, muscular sac which encloses a convoluted,tubular seminal vesicle in the bunocotylid Opisthadena dimidia Linton, 1910. It appears to be amodification of the muscular type of seminal vesicle where the muscular wall is clearly notassociated with the membranous lining of the seminal vesicle. It also occurs in some of the otherspecies of Opisthadena and in the hemiurid Elytrophalloides. Seminal vesicle - a dilation of the vas deferens (q.v.) which forms a store of spermatozoa whichis ready for ejaculation. It is often provided with a muscular wall or with sphincter muscles whichconstrict it into portions. These modifications, which are often of systematic importance at thegeneric level, are involved with the evacuation of spermatozoa from the seminal vesicle, throughthe pars prostatica and into the hermaphroditic duct, often against the hydrostatic pressure pro-duced by the sinus-sac (q.v.). The shape of the seminal vesicle is also often of specific or genericvalue, as is its position in relation to the ventral sucker. In the more primitive forms it is usuallytubular. In the hemiuroids the seminal vesicle is normally free in the parenchyma, but in certainhalipegine derogenids it may be partly or completely enclosed within the sinus-sac., in the azygiidsit is contained within a prostatic sac (q.v.), and in certain species of Opisthadena it forms a'seminal sac' (q.v.). Sinus-organ (permanent) - a copulatory organ of variable size which is usually formed externallyfrom the wall of the normally well-developed genital atrium and internally from the herma-phroditic duct. This type of sinus-organ is contractile, but is still visible in sections as a smallcone when completely retracted. It usually occurs in one of two forms, although intermediateforms are sometimes found (Fig. 5): B tso Fig. 5 The types of sinus-organ occurring in the Hemiuroidea: A. Muscular sinus-organ;B. Amuscular sinus-organ; C. Temporary sinus-organ, [so, permanent sinus-organ; ss, sinus-sac;tso, temporary sinus-organ.] 52 D. I. GIBSON & R. A. BRAY (1) 'Muscular' - where it is probably everted entirely or partly by its own intrinsic musculature(when partly, the remaining force is supplied by hydrostatic pressure produced by the sinus-sac:see Gibson & Bray, 1974): this form occurs in many of the more primitive hemiuroid groups(see p. 129); (2) 'Amuscular'* - a form, associated with the presence of a thick-walled (muscular) seminalvesicle, which is probably everted entirely, or almost entirely, by hydrostatic pressure producedby the sinus-sac upon its contents: this form occurs in the elytrophalline and glomericirrinehemiurids, the muscular seminal vesicle being required to force spermatozoa into the herma-phroditic duct against the hydrostatic pressure built up by the walls of the sinus-sac. The presence or absence and type of sinus-organ are often useful taxonomic criteria up to thesubfamily level; but the sectioning of specimens is essential and great caution must be exercisedin the use of this feature. See sinus-organ (temporary). Sinus-organ (temporary) - an amuscular or weakly muscled copulatory organ, formed from thehermaphroditic duct by hydrostatic pressure within the sinus-sac, which is a transitory structure(Fig. 5). It is usually only present during copulation, but also occurs occasionally in fixed speci-mens. The genital atrium is usually small or apparently absent in forms with a temporary sinus-organ. Naturally 'permanent' [see sinus-organ (permanent)] and 'temporary' types of sinus-organcannot occur in the same species of worm. The two forms, however, may be difficult to distinguishwhen only a small number of specimens is available for study. A temporary sinus-organ may beassociated with slight thickenings in the wall of the seminal vesicle, but is more often associatedwith the presence of sphincter muscles which tend to partition the seminal vesicle and are capableof exerting pressure, thus forcing spermatozoa into the sinus-sac against its internal hydrostaticpressure during ejaculation. As the genital atrium tends to be short or absent, the temporarysinus-organ itself is also short, and, therefore, the hydrostatic pressure required to extrude it isreduced. The sinus-sac tends, therefore, to be smaller than in forms with an amuscular permanentsinus-organ. A temporary sinus-organ occurs in the more advanced forms of hemiurids, bunocoty-lids and lecithasterids. As this transitory structure is rarely seen everted, it is of no systematicsignificance. Sinus-sac or hermaphroditic sac - a muscular sac which surrounds the base of the genital atrium,if present, and encloses the hermaphroditic duct and/or the terminal portions of the ejaculatoryduct and uterus. Its apparent function is to aid the eversion of a permanent sinus-organ (q.v.) orthe production of a temporary sinus-organ (q.v.) from the hermaphroditic duct. It may also aidthe expulsion of spermatozoa and eggs, especially the former in cases where an ejaculatory (orprostatic) vesicle (q.v.) or the seminal vesicle is enclosed within the sinus-sac. In certain instances,e.g. in some of the plerurine hemiurids, there may be a large proximal gap in the wall of thesinus-sac at the point through which the male and female ducts pass: this is known as an 'open-type' of sinus-sac and is probably a vestigial form. In other groups of hemiuroids the sinus-sacmay be reduced, or in some cases completely lost. Sectioning is essential when the sinus-sac isapparently absent, as the vestiges of this structure are often insignificant. This feature is frequentlyof some importance at the family level, as it is missing in the Azygiidae and Hirudinellidae, whichpossess a 'prostatic sac' (q.v.) and a 'cirrus-sac' (q.v.), respectively; but great care should beexercised in the utilization of this feature, as it appears to have been lost independently in certaingenera from a number of distantly related hemiuroid groups, e.g. Gonocerca, Syncoelium,Tetrochetus, Prolecitha and Bunocotyle. Temporary sinus-organ - see sinus-organ (temporary). Testes - there are usually two globular testes present in hemiuroids. Exceptions are the syncoeliids,which either have a much larger number (11-18) of large oval masses (referred to as testes, al-though there are only two vasa erTerentia) or possess apparently follicular testes, and two lecithas-terid genera, Monorchiaponurus and Monorchimacradena, which are reported to have one testis. * Presumably there are some longitudinal muscle fibres present which permit contraction of this type of sinus-organ. THE HEMIUROIDEA 53 An important feature at the subfamily level (except in some members of the Macradenininae)is the relationship between the ovary and the testes, the ovary usually being post-testicular. Inthe azygiine azygiids, the ptychogonimids, the gonocercine derogenids and certain macradenininelecithasterids, however, it is pretesticular, and in the bathycotylids it is inter-testicular. Therelative positions of the testes and their shape are of little value above the specific level, exceptthat in the dictysarcid genus Elongoparorchis they do appear to be consistently elongate. Thetestes normally occur in the hindbody, except in the prosogonotrematine and prosorchiinesclerodistomids. Uroproct - the aperture of the excretory vesicle when the base of the latter organ communicatesdirectly with the distal extremities of the gut-caeca. A uroproct, therefore, serves as an orifice forthe evacuation of waste-products from both the excretory and alimentary systems. This structureoccurs independently and regularly in the Accacoeliidae, Hirudinellidae, Ptychogonimidae andOtiotrematinae, but, except for the Accacoeliinae and the Ptychogonimidae, it does not occur inall of the genera in these groups. It is normally considered to be a feature of generic importance. Uterine ootype - the proximal region of the uterus, present in some species, into which the regionof egg-formation extends. Its systematic importance is not understood. See ootype. Uterine seminal receptacle or receptaculum seminis uterinum - a term given to the proximal regionof the uterus when it is filled with 'fresh' spermatozoa and is, therefore, acting as a seminal store(Fig. 1). This region can normally only be differentiated from the remainder of the uterus by thepresence of spermatozoa. It is the commonest form of seminal receptacle (q.v.) present in theHemiuroidea, being absent only in the lecithasterids (with the exception of the Hysterolecithinae),the opisthadenine bunocotylids and in the derogenids Progonus and Leurodera. This type ofseminal receptacle is probably associated with cross-insemination, using the genital atrium as avagina, or with self-insemination, and differs from all other types of seminal receptacle in thatspermatozoa pass towards the ovary through the ootype. In the past many workers have mistakenthis structure for a canalicular seminal receptacle (q.v.), but in sectioned material the two caneasily be distinguished. Except in the cases of the derogenids Progonus and Leurodera, the presenceor absence of this type of seminal receptacle is an important systematic feature at the subfamilylevel. Great care must be exercised with the use of this feature because it is by nature transitory,and, when empty, it is not recognizable as a seminal store. We have observed, in sectionedmaterial, specimens of Hirudinella and Prosorchiopsis (forms possessing a uterine seminal recep-tacle) which do not have any spermatozoa in the proximal region of the uterus. Uterus - a duct, normally full of eggs, which links the ootype with the hermaphroditic duct,genital atrium or genital pore. The distal extremity may be modified to a form metraterm (q.v.),and the proximal extremity may form a uterine seminal receptacle (q.v.) or a uterine ootype (q.v.).In addition to transporting eggs, the proximal region of the uterus appears to be involved in thehardening and tanning of the egg-shells. The uterus often coils between the ovary and the ventralsucker, but it may loop well posterior to the ovary and in some cases coils in the forebody. Itsdistribution tends to be of generic importance and occasionally of subfamilial importance,especially in cases where it reaches into the post-ovarian field or is entirely pre-ovarian. Vasa efferentia - single narrow ducts which connect each testis with the vas deferens (q.v.). Inthe Syncoeliinae, where there are 11-18 so-called testes, there are the usual two vasa efferentia,and the ducts linking these testes to the vasa efferentia are called 'collecting ducts'. The vasaefferentia are of no apparent systematic importance in the Hemiuroidea. Vas deferens - a duct formed by the fusion of the two vasa efferentia (q.v.), which, in almost allcases, is dilate, filled with spermatozoa and referred to as the seminal vesicle (q.v.). In itself,therefore, it is of no systematic importance, although in certain groups there is a narrow ductlinking the seminal vesicle with the pars prostatica (q.v.). Ventro-cervical groove - a transverse crevice which occurs on the ventral surface immediatelyanterior to the ventral sucker in many hemiurids. It appears to have no actual function, as it is 54 D. I. GIBSON & R. A. BRAY simply caused by the close proximity of the oral and ventral suckers in some of these genera. Thesize of this feature appears to be dependent upon the degree of contraction which occurs in theforebody during fixation. It appears to have no systematic value, except that it has occasionallybeen mistaken for a presomatic pit (q.v.). Vitellarium - a structure of variable morphology that produces vitelline (yolk) cells whichaccompany the ovum in egg-formation. The form of the vitellarium is a valuable taxonomiccriterion ranging from the species to the family level. The common arrangements of the vitellariumin the Hemiuroidea are as follows (see Fig. 7): (1) follicular; (2) linked follicles, giving a chain-like tubular arrangement; (3) convoluted tubules which are often branched; (4) about seventubules, usually arranged four on one side of the body and three on the other; (5) about sevenoval to digitiform lobes; (6) two oval or slightly lobed masses; and (7) a single oval mass. Theseforms tend to grade into one another, but it is noticeable that the seven-lobed vitellarium occurswidely throughout the group. The arrangement of the vitellarium is discussed in more detail onp. 124. One unusual feature occurs in the Accacoeliinae, where the sinistral side of the system isreduced to a vestige. In certain instances, especially in the Lecithasteridae and the Derogenidae,the relationship between the vitellarium and the ovary is useful systematically; but the vitellariumor at least the origin of the main vitelline ducts is usually post-ovarian, although exceptions tothis include the azygiids and the accacoeliine accacoeliids. III. A classification of the Hemiuroidea with keys and definitionsIntroduction The following classification, which we propose for the Hemiuroidea, is based upon adult morpho-logy associated with an attempt to understand the function of the organs and organ-systems(see p. 39). This relies heavily upon comparative morphology, as do most of the previous classi-fications. The main problem with this, as discussed above, is that much of the descriptive workover the years has been inadequate. Many workers around the turn of the century gave detailedand careful descriptions, based upon sectioned material. Work of this standard has been theexception, rather than the rule, since that time. In attempting to provide a feasible classificationwe have, therefore, examined as many species as possible, both in serial sections and whole-mounts. The lack of certain material has left large gaps, which have had to be filled with a criticalappraisal of the literature. In certain groups, and in particular in many individual genera, muchof the detail necessary to classify the animals has not been supplied by the original authors. Inthese cases our classification is particularly tentative, and we have usually indicated where weconsider our knowledge to be totally inadequate. In some instances, using our knowledge of thegroups as a whole and assessing the functional requirements present, we have assumed themorphology of certain undescribed or apparently wrongly interpreted structures. While thismay seem somewhat unsatisfactory, some of our interpretations were proved correct during thecourse of the work, e.g. before specimens were obtained we correctly assumed the presence of asinus-sac, rather than a cirrus-sac, in Arnold and Glomericirrus, and we correctly assumed thepresence of Juel's organ in Elongopat -orchis and in many of the hemiurids (sensu stricto). As far as the systematics of this group is concerned, we have faced many problems in weighingthe relative values of different factors. At one time we were inclined to give considerable weightto the details of the terminal genitalia, and also to the vitellarium. While these factors may havesignificance at the generic or subfamily level, they do seem to be susceptible to development orregression in certain groups. The details of the proximal region of the female system have, webelieve, a fundamental value in distinguishing subfamilies, although there are exceptions to this,for in the Derogenidae and the Trifoliovariinae a variety of conditions occur. The presence ofJuel's organ, for example, seems to be of considerable importance; but, even in this case, carehas to be taken, and the complete morphological pattern must be taken into consideration. Definitions of the taxa are presented ; but features common to a group of taxa are given in thedefinition of the higher taxa, rather than repeated throughout the group. Features, especially THE HEMIUROIDEA 55 those taken from the literature, which we believe to be questionable, are indicated by question-marks. Wherever possible material was examined, especially in serial section. The abbreviations usedto indicate what material we have seen are given after the generic name, and are as follows:T=type-material of type-species; t=non-type material of type-species ; n=material of non-type-species; w=whole-mount; s=serial sections. The absence of this information indicates that thedata have been derived from the literature. We have attempted to provide dichotomous keys to the taxa. Rather than relying upon themost obvious of criteria, we have tried to produce keys which work, with the result that the sec-tioning of material, while always advisable, may in fact be essential. These keys must be usedwith care, and with the understanding that this classification is based upon polythetic assemblagesof characters. Soft-bodied animals, such as digeneans, give few good metrical or meristic charac-ters, so that it is very important to possess a good understanding of the overall morphology whileattempting to determine these worms. Some readers may note that the authorities which we have given for some of the family-group names differ from those presented by some other workers. These workers appear to havefollowed a recent trend which tends to confuse systematics and nomenclature. In using theauthority for the original mention of the family-group name, irrespective of suffix, we are follow-ing Article 36 of the International Code of Zoological Nomenclature. As with any work of this kind, our classification must be considered provisional. We hope thatit may be helpful in stimulating and encouraging a closer and more careful examination of theworms in this group. Superfamily HEMIUROIDEA Looss, 1899 Azygioidea Liihe, 1909Accacoelioidea Odhner, 1911Isoparorchioidea Travassos, 1922 Body small to large; oval to cylindrical. Ecsoma present or absent. Body-surface smooth, rugateor plicated (or 'scaley'); never spiny, but occasionally papillate. Oral and ventral suckers welldeveloped, occasionally small. Ventral sucker normally in middle or anterior half of body,occasionally just inside posterior half of body; occasionally pedunculate. Prepharynx absent.Pharynx well developed; normally oval, occasionally modified. Oesophagus usually short,occasionally long. 'Driisenmagen' present or absent. Gut-caeca usually end blindly near posteriorextremity, occasionally form cyclocoel or uroproct. Testes normally two, rarely one or follicular;normally tandem to symmetrical, preovarian and near middle of body; occasionally in forebodyor post-ovarian. Seminal vesicle oval to tubular; occasionally constricted into portions usuallythin- but occasionally thick-walled; in fore- or hindbody; normally external to sinus-sac, rarelypartly or entirely internal. Pars prostatica tubular to vesicular; long or short; normally externalto sinus-sac, rarely internal; usually in forebody, occasionally entirely inside, or extending into,hindbody. Ejaculatory duct usually present; usually short; often within sinus-sac or sinus-organ;normally unites with metraterm to form hermaphroditic duct; occasionally within 'cirrus-sac'.Hermaphroditic duct usually present; usually within sinus-sac and/or sinus-organ. Sinus-sacpresent or absent; oval to cylindrical; normally enclosing ejaculatory duct and part of metratermand/or hermaphroditic duct; occasionally additionally enclosing ejaculatory (prostatic) vesicleor seminal vesicle and/or pars prostatica. Permanent sinus-organ present or absent within genitalatrium; conical to tubular; muscular or non-muscular. Temporary sinus-organ sometimes formedfrom hermaphroditic duct. 'Cirrus-sac', enclosing ejaculatory duct only, and 'cirrus' rarelypresent. Genital atrium large, small or absent. Common genital pore mid-ventral in forebody.Ovary usually oval, occasionally lobed, rarely tubular or follicular; usually post-testicular,occasionally pre-testicular, rarely inter-testicular; normally in hindbody, rarely in forebody.Mehlis' gland usually post-ovarian, occasionally pre-ovarian. Uterine seminal receptacle plusLaurer's canal and/or Juel's organ or blind seminal receptacle alone normally present. Uterinecoils usually fill much of hindbody, occasionally extending well into forebody, rarely entirely inforebody. Eggs normally oval; usually small, numerous; occasionally with spine, filament(s) or 56 D. I. GIBSON & R. A. BRAY threads. Vitellarium normally follicular, tubular or composed of a small number (often seven)oval to tubular lobes or one to three (usually two) entire or lobed masses; often post-ovarian,occasionally pre-ovarian; sometimes extending throughout hindbody or into forebody, rarelyentirely in forebody. Excretory pore terminal; vesicle Y-shaped; arms united in forebody or not.Manter's organ (accessory excretory vesicle) rarely present. Parasitic in gut, especially stomach,primarily of marine teleosts, but commonly occur in freshwater teleosts and elasmobranchs,occasionally in holosteans, amphibians, reptiles and progenetic in invertebrates; occasionallyrecorded from gills, skin, body-cavity, swim-bladder and other organs. Key to Hemiuroidea 1. A. Vitellarium composed of numerous widely distributed follicles ..... (2)B. Vitellarium otherwise, usually composed of a small number of oval to tubular (occasion-ally branched) lobes or 1-3 distinct oval, lobed or unlobed masses .... (3) 2. A. Prostatic sac present; parasitic in elasmobranchs and freshwater teleosts AZYGIIDAE (p. 60)B. Prostatic sac absent; parasitic in gut of elasmobranchs . PTYCHOGONIMIDAE (p. 110) 3. A. Testes 2, occasionally 1 ............ (4) B. Testes follicular, 11-18 large or many small follicles arranged in rows or irregularly dis-tributed; usually parasitic in buccal or branchial cavities or on skin (? occasionallyinternally) of elasmobranchs and marine teleosts . . . SYNCOELIIDAE (p. 114) 4. A. Ecsoma absent (take care with this observation as some hemiurids have a reduced ecsoma and some bunocotylids may retain the vestige of an ecsoma) ..... (5)B. Ecsoma present (sometimes very reduced); body surface often plicated; Juel's organ anduterine seminal receptacle present; vitellarium varies between form with 7 tubularlobes and form with 2 distinct oval masses; parasitic mainly in gut of marine teleosts,occasionally present in freshwater teleosts and lung of sea-snakes HEMIURIDAE (p. 84) 5. A. Ovary usually post-testicular, occasionally pre-testicular ...... (6) B. Ovary inter-testicular; parasitic on gills (? and in stomach) of marine teleosts BATHYCOTYLIDAE (p. 62) 6. A. Ovary oval or lobed ............ (7) B. Ovary tubular; parasitic in swim-bladder of freshwater teleosts ISOPARORCHIIDAE (p. 100) 7. A. Ventral sucker anterior to middle of body; parasitic in marine teleosts; seminal vesicle never enclosed in sinus-sac ........... (8) B. Ventral sucker usually in or near middle of body, occasionally more anterior; significantproportion of uterus usually present in forebody [a small number of marine forms dopossess a ventral sucker in the anterior half of the body and uterine coils which do notextend into the forebody, but these forms also possess a seminal vesicle which is enclosedwithin the sinus-sac]; vitellarium 1 or 2 masses, entire or lobed (lobes normally shallow,rarely digitate); seminal vesicle in forebody; ovary and vitellarium pre- or post-testicular; parasitic mainly in gut of freshwater and marine teleosts, occasionally inamphibians, reptiles and freshwater shrimps .... DEROGENIDAE (p. 71) 8. A. 'Cirrus' present, enclosed in 'cirrus-sac'; female duct opens into genital atrium indepen- dently; large parasites from gut ( ? or gills) of marine teleosts (immature forms occasion-ally present in salmonids) HIRUDINELLIDAE (p. 98) B. 'Cirrus' and 'cirrus-sac' absent ; male and female ducts normally unite forming hermaphro-ditic duct, which is often present within a sinus-organ and enclosed by a sinus-sac . (9) 9. A. Parasitic in gut (occasionally on gills) (10) B. Parasitic in swim-bladder or gall-bladder . ........ (13) 10. A. Vitellarium 1, 2 or 3 compact masses .... BUNOCOTYLIDAE (p. 62)B. Vitellarium otherwise . . . . . . . . . . . . (11) 1 1. A. Vitellarium 6-8 (occasionally twice this number) oval to digitiform lobes, often arranged in rosette, occasionally branched ; Manter's organ absent ; pharynx oval LECITHASTERIDAE (p. 101)B. Vitellarium tubular (filamentous) (12) 12. A. Manter's organ present; pharynx oval .... SCLERODISTOMIDAE (p. Ill)B. Manter's organ absent; pharynx with narrow anterior extension into base of oral sucker; occasionally present on gills; commonly parasitic in sunfish (Molidae) ACCACOEL1IDAE (p. 57) THE HEMIUROIDEA 57 13. A. Parasitic in swim-bladder; vitellarium 6-8 oval to digitiform lobes, 2 compact multilobu- late masses or 2 acinous groups of follicles .... DICTYSARCIDAE (p. 81)B. Parasitic in gall-bladder; vitellarium tubular, dendritic, with anteriorly and posteriorly oriented main collecting ducts situated medially . SCLERODISTOMOIDIDAE (p. 114) Family ACCACOELIIDAE Odhner, 1911 Body large or small, commonly elongate. Ecsoma absent. Body-surface smooth, but forebodymay be papillate. Oral and ventral suckers well developed. Ventral sucker normally in anteriorhalf of body; may be pedunculate. Pharynx well developed; with narrow anterior extension intobase of oral sucker; occasionally modified posteriorly. Oesophagus usually long, occasionallyshort. 'Driisenmagen' present. Gut-caeca usually H-shaped; terminate blindly or more commonlyform uroproct. Testes two; oblique or in tandem; in hindbody, normally close to middle of body;pre-ovarian. Seminal vesicle thin-walled; tubular; sinuous or convoluted; commonly reachinginto hindbody. Pars prostatica tubular; external gland-cells may be delimited. Short ejaculatoryduct commonly present within sinus-sac. Hermaphroditic duct present or absent. Sinus-sac andsinus-organ present or absent. Genital atrium present. Ovary oval ; post-testicular. Mehlis' glandpre- or post-ovarian ; linked to anterior or posterior region of ovary by oviduct. Laurer's canaland uterine seminal receptacle present. Juel's organ and canalicular or blind seminal receptacleabsent. Uterus extensive; coils entirely or almost entirely in hindbody; usually passes close toposterior extremity before looping forward again. Eggs numerous; small; non-filamented.Vitellarium with one or two main collecting ducts ; composed of numerous filamentous tubules(? or occasionally chains of follicles) in various parts of the fore- or hindbody. Excretory vesicleY-shaped ; arms initially in dorsal and ventral fields, united in forebody. Metacercariae usually incoelenterates or ctenophores. Parasitic in gut or occasionally on gills of marine teleosts. COMMENT The vitellarium of the Paraccacladiinae is typical of many of the primitive hemiuroids,possessing a symmetrical pair of main collecting ducts which branch distally and unite proximallyto form a common collecting duct. In the Accacoeliinae, however, it appears that the right half ofthe vitelline system is reduced to a small vestigial process (or reservoir). The whole of the vitellinesystem of the latter group, therefore, corresponds to only the left-hand side of the vitellarium inother hemiuroids. Key to Accacoeliidae 1. A. Oesophagus long and narrow; gut-caeca H-shaped; uroproct present; Mehlis' gland pre-ovarian, linked to anterior region of ovary by oviduct; vitellarium with single maincollecting duct and system of branching tubules . . ACCACOELIINAE (p. 57) B. Oesophagus short; gut-caeca not distinctly H-shaped and end blindly; Mehlis' gland post-ovarian, linked to posterior region of ovary by oviduct; vitellarium with symmetricalpair of collecting ducts and system of branching tubules . PARACCACLADIINAE (p. 59) Subfamily ACCACOELIINAE Odhner, 1911 Tetrochetinae Looss, 1912, emend. Dollfus, 1935Accacladiinae Yamaguti, 1958Orophocotylinae Yamaguti, 1958Rhynchopharynginae Yamaguti, 1958Guschanskianinae Skrjabin, 1959 Body usually elongate. Body-surface smooth, but forebody may be papillate. Lateral flangesoccasionally present on ventral sucker. Pharynx occasionally modified to form two muscularbulbs (Rhynchopharynx). Oesophagus long and thin. Gut caeca H-shaped. Uroproct present.Sinus-sac and sinus-organ present or absent; sinus-sac well or poorly developed when present.Mehlis' gland pre-ovarian; linked by oviduct to anterior region of ovary. Vitellarium filamentous;with single main collecting duct on right and single system of ramifying branches in fore- orhindbody; left-hand system reduced to small process or small ramifying system. Parasitic ongills or in gut of marine teleosts (especially Molidae). 58 D. I. GIBSON & R. A. BRAY Key to Accacoeliinae 1. A. Well-defined sinus-sac and sinus-organ present ........ (2) B. Well-defined sinus-sac and sinus-organ absent ........ (5) 2. A. Ectoparasitic on gills; long proboscis-like sinus-organ; strongly developed ventral muscu- lature in hindbody; enormous pars prostatica occupying much of forebody; vitellarium posterior to anterior testis ACCACOELIUM B. Endoparasitic in gut; short cylindrical or dome-shaped sinus-organ; vitellarium not usually extending posteriorly to ovary ......... (3) 3. A. Pharynx pyriform with anterior extension into base of oral sucker .... (4)B. Pharynx with two bulbs and anterior elongate portion ensheathed in glandular posterior process of oral sucker; glandular oesophageal bulb immediately posterior to pharynx; large glandular organ of unknown function at base of peduncle RHYNCHOPHARYNX 4. A. Vitellarium confined to hindbody; ventral sucker on extensible peduncle; pars prostatica relatively short ACCACLADIUM B. Vitellarium wholly or partly in forebody; ventral sucker sessile or nearly so; pars prostatica long ACCACLADOCOELWM 5. A. Diffuse muscular region around metraterm; muscular sucker-like pads on antero-dorsal surface ODHNERWM B. No sinus-sac detectable; no muscular pads present on antero-dorsal surface . . . (6) 6. A. Vitellarium a tubular branching structure on either side of hindbody; no flange on ventral sucker TETROCHETUS B. Vitellarium comprising (?) few follicles in four rows between the anterior testis and the base of the peduncle; small flange on ventral sucker . . . OROPHOCOTYLE ACCACOELIUM Monticelli, 1893 [t(w,s)] Forebody papillate. Oesophagus reaches to ventral sucker. Ventral sucker on short peduncle.Thick muscular layer in ventral hindbody. Sinus-sac present surrounding base of genital atrium.Sinus-organ long and strongly muscular, frequently extended through genital pore. Enormouspars prostatica and associated gland-cells occupy much of forebody. Vitellarium posterior toanterior testis. Parasitic on gills of marine teleosts (Mola). TYPE-SPECIES. Accacoelium contortum (Rudolphi, 1819) [by subsequent designation: Looss, 1899]. ACCACLADIUM Odhner, 1928 [t(w,s>] Body-surface smooth. Oesophagus reaches to ventral sucker. Ventral sucker on extensiblepeduncle. Pars prostatica well developed. Sinus-sac surrounding base of genital atrium. Sinus-organ short, cylindrical. Vitellarium between ventral sucker and ovary. Parasitic in intestine ofmarine teleosts (Mola). TYPE-SPECIES. Accacladium serpentulus Odhner, 1928 [by original designation]. ACCACLADOCOELWM Odhner, 1928 [t(w,s); n(w,s)] Guschanskiana Skrjabin, 1959 Body smooth. Lateral flanges on ventral sucker present or absent. Oesophagus reaches to ventralsucker. Pars prostatica long. Sinus-sac present surrounding base of genital atrium. Sinus-organshort, cylindrical. Vitellarium reaches anteriorly to oral sucker, may extend posteriorly just pastovary but usually not beyond anterior testis; reduced fraction may branch. Parasitic in intestineof marine teleosts (Mola). TYPE-SPECIES. Accacladocoelium nigroflavum (Rudolphi, 1819) [by original designation]. ODHNERWM Yamaguti, 1934 [t(w,s)] Mneiodhneria Dollfus, 1935 Caballeriana Skrjabin & Guschanskaja, 1959 THE HEMIUROIDEA 59 Body-surface smooth, but with muscular sucker-like pads on antero-dorsal surface. Flange-likemuscular extensions present on ventral sucker; latter pedunculate. Oesophagus reaches toventral sucker. Pars prostatica reaches half-way back to ventral sucker. Diffuse muscular regionsurrounds distal parts of metraterm and genital atrium (may be vestige of sinus-sac). Male ductenters genital atrium from side through small papilla. Vitellarium tubular, extending from pharynxto ovary. Parasitic in intestine of marine teleosts (Mold). TYPE-SPECIES. Odhnerium calyptrocotyle (Monticelli, 1893) [by original designation]. COMMENT. We are using the appellation Odhnerium rather than Mneiodhneria, despite its similarityto Odhneria Travassos, 1921, in accordance with the International Code of ZoologicalNomenclature. OROPHOCOTYLE Looss, 1902 [Inadequately described.] Body-surface smooth. Ventral sucker pedunculate; bears small flange.Oesophagus not reaching to ventral sucker. Pars prostatica short. Sinus-sac not reported. Sinus-organ absent. Vitellarium reported to consist of few (?) follicles in four rows between testes andventral sucker. Parasitic in intestine of marine teleosts (Ranzanid). TYPE-SPECIES. Orophocotyle planci : (Stossich, 1899) [by original designation]. RHYNCHOPHAR YNX Odhner, 1928 [t(w,s)] Forebody papillate. Ventral sucker pedunculate. Pharynx consisting of two muscular bulbs [the'pharynx-proper' and the 'Russelblase' (snout-bladder)] and an extended anterior snout ('Russel'),which may be extended through the oral sucker. Oral sucker possesses posterior glandularextension, the snout-sheath ('Russelscheide'), which envelopes the snout. Glandular oesophagealbulb present immediately posterior to pharynx. Oesophagus reaches to ventral sucker. Largeglandular organ of unknown function present at base of peduncle. Pars prostatica long. Sinus-sac surrounds base of genital atrium. Sinus-organ small. Vitellarium extends from anterior regionof ventral sucker to ovary. Parasitic in intestine of marine teleosts (Mold). TYPE-SPECIES. Rhynchopharynx paradoxa Odhner, 1928 [by original designation]. TETROCHETUS Looss, 1912 [t(w,s) ; n(w,s)] Paratetrochetus Hanson, 1955 Body-surface smooth. Ventral sucker pedunculate. Oesophagus long. Diverticula present atintestinal bifurcation. Pars prostatica short, straight, narrow. Sinus-sac and sinus-organ absent.Male and female ducts open together into shallow genital atrium. Vitellarium tubular, in hind-body; reduced half may be branched. Parasitic in intestine of medusophagus and carnivorousmarine teleosts. TYPE-SPECIES. Tetrochetus raynerii (Nardo, 1833) [by monotypy]. Subfamily PARACCACLADIINAE Bray & Gibson, 1977 Body elongate. Body-surface smooth, but with papillae on outer surface of ventral sucker. Ventralsucker on short peduncle. Pharynx extended into base of oral sucker. Oesophagus short, wide.Anterior caecal shoulders small. Gut-caeca terminate blindly near posterior extremity. Parsprostatica elongate, convoluted. Sinus-sac present surrounding base of genital atrium; muscula-ture diffuse. Sinus-organ short, cylindrical. Mehlis' gland post-ovarian; linked to posterior regionof ovary by oviduct. Vitellarium with symmetrical pair of main collecting ducts and ramifyingsystems of tubules; posterior to ovary. Mature forms parasitic in rectum of carnivorous marineteleosts (Coryphaenoides) ; immature forms parasitic in rectum of medusophagus marine teleosts. 60 D. I. GIBSON & R. A. BRAY PARACCACLADIUM Bray & Gibson, 1977 [T(w,s)] Defined as subfamily.TYPE-SPECIES. Paraccacladiwn jamiesoni Bray & Gibson, 1977 [by original designation]. Family AZYGHDAE Liihe, 1909Aphanhysteridae Guiart, 1938 Body large or small ; usually elongate. Ecsoma absent. Body-surface smooth, without spines orplications. Oral and ventral suckers well developed ; latter in middle or anterior half of body.Prepharynx absent. Pharynx well developed. Oesophagus usually short. 'Driisenmagen' apparentlyabsent. Gut-caeca terminate blindly close to posterior extremity. Testes two; in tandem, obliqueor symmetrical; pre- or post-ovarian in hindbody. Seminal vesicle tubular, usually short, thin-walled; convoluted in forebody. Pars prostatica tubular. Prostatic sac present surrounding parsprostatica and seminal vesicle. Ejaculatory duct usually long and convoluted, but of variablelength. Hermaphroditic duct short; at distal extremity of sinus-organ. Permanent sinus-organvariable in length; usually conical. Sinus-sac absent. Genital atrium usually well developed;variable in size. Genital pore mid- ventral in forebody. Ovary oval; pre- or post-testicular. Mehlis'gland pre-ovarian. Laurer's canal and uterine seminal receptacle present. Juel's organ andcanalicular or blind seminal receptacle absent. Uterus entirely or almost entirely pre-ovarian;coiled mainly in hindbody. Eggs numerous; small; non-filamented. Vitellarium follicular; usuallypresent laterally throughout much of hindbody; occasionally extending into forebody. Excretoryvesicle Y-shaped ; arms united in forebody or not. Parasitic in stomach or body-cavity of elasmo-branchs and in stomach of freshwater teleosts and holosteans. Key to Azygiidae LA. Testes post-ovarian AZYGIINAE (p. 60) B. Testes pre-ovarian LEUCERUTHRINAE (p. 62) Subfamily AZYGIINAE Liihe, 1909 Aphanhysterinae Guiart, 1938Gomtiotrematinae Gupta, 1955Allogomtiotrematinae Yamaguti, 1958Proterometrinae Yamaguti, 1958 Body normally large; occasionally small. Ventral sucker larger or smaller than oral sucker; inmiddle or anterior half of body. Testes in tandem, oblique or symmetrical; post-ovarian. Uterusentirely pre-testicular. Vitelline field may extend into forebody. Excretory arms may or may notunite in forebody. Parasitic in stomach or body-cavity of elasmobranchs and stomach of fresh-water teleosts and holosteans. Key to Azygiinae 1 . A. Testes symmetrical ; vitelline follicles and uterine coils extending into forebody ; testes near posterior extremity; in freshwater teleosts (N. America) . . . PROTEROMETRAB. Testes tandem, oblique, or occasionally symmetrical; vitelline follicles and uterine coilsentirely or almost entirely confined to hindbody; testes usually well anterior to posteriorextremity ......... . 2. A. Vitelline follicles confluent posterior to testes; ventral sucker normally larger than oral sucker; parasitic in elasmobranchs. ...... OTODISTOMUM B. Vitelline follicles not confluent posterior to testes; oral sucker normally larger than ventral sucker; parasitic in freshwater teleosts and holosteans ..... AZYGIA THE HEMIUROIDEA 61 AZYGIA Looss, 1899 [t(w,s)] Megadistomum Stafford, 1904Mimodistomum Stafford, 1904Hassallius Goldberger, 1911Eurostomum MacCallum, 1921Gomtiotrema Gupta, 1955, nee Sinha, 1934Allogomtiotrema Yamaguti, 1958 Body medium to large; usually elongate, occasionally oval. Ventral sucker smaller than oralsucker; in anterior half of body. Testes tandem, occasionally to symmetrical; anterior testisoccasionally lateral to ovary (A. asiatica). Sinus-organ a small papilla-like structure. Uterinefield between ovary and ventral sucker. Vitelline follicles confined to hindbody; not confluentposterior to testes. Excretory arms apparently not united in forebody. Parasitic in stomach andintestine of freshwater teleosts and holosteans. TYPE-SPECIES. Azygia lucii (Mu'ller, 1776) [by subsequent designation: Goldberger, 191 la]. COMMENT. Yamaguti (1971) recognizes two subgenera, Azygia Looss, 1899, and PseudazygiaYamaguti, 1971. He distinguishes these by the length of the post-testicular region and the positionof the bifurcation of the excretory vesicle. The former criterion appears to be a somewhat variablefeature in Azygia asiatica Simha & Pershad, 1964, and in A. angusticauda (Stafford) of Kakaji(1968; ? synonym of A. asiatica). OTODISTOMUM Stafford, 1 904 [t(w,s) ; n(w,s)] Xenodistomum Stafford, 1904Josstaffordia Odhner, 1911*Aphanhystera Guiart, 1938 Body large; spatulate to elongate. Ventral sucker larger than oral sucker; close to anteriorextremity. Testes tandem or slightly oblique. Sinus-organ capable of considerable extension orcontraction to form small papilla. Uterine field almost entirely between ovary and ventral sucker.Vitelline follicles extend in lateral fields posterior to ventral sucker, reaching back to post-testicular region where fields are confluent. Excretory arms usually unite in forebody, but occas-ionally do not. Parasitic in stomach or body-cavity of elasmobranchs (sharks, rays and chimaeras). TYPE-SPECIES. Otodistomum veliporum (Creplin, 1837) [by monotypy]. COMMENT. It is worth noting that there are two body-forms present in this genus, which appearto be related to their location within the host. The species parasitic within the body-cavity tendto be broad or spatulate, whilst those parasitic in the stomach are very elongate. It is possiblethat the spatulate body-shape has been evolved to prevent these parasites being lost through theabdominal pores, and it is noticeable that the gorgoderid and monogenean parasites from thebody-cavity of elasmobranchs are also spatulate or oval. Elasmobranchs are the only group ofvertebrates which commonly harbour adult helminths in the body-cavity: this is because theabdominal pores form an exit for the release of eggs. The excretory arms in species of Otodistomumare normally considered to unite in the forebody; but in sectioned material of O. plunketi Fyfe,1953, they end blindly (Gibson & Bray, 1977). PROTEROMETRA Horsfall, 1933 Body oval; small. Oral sucker large; ventral sucker small, situated at or just posterior to middleof body. Testes symmetrical at posterior extremity. Sinus-organ a small cone. Uterine fieldextends from ovary into forebody. Vitellarium extends from level of testes or ovary anteriorly * The appellation Josstaffordia josstaffordi n.g., n.sp. was proposed by Odhner (1911) for specimens of Otodistomumin a sarcastic footnote, mimicking the erection of Hassallius hassalli by Goldberger (191 la). Although he givesindications as to its distinctive features, it is obvious that Odhner did not intend it to be considered valid. 62 D. I. GIBSON & R. A. BRAY well into forebody, in lateral fields. Excretory arms united in forebody. Parasitic in gut of fresh-water teleosts (in North America). TYPE-SPECIES. Proterometra macrostoma (Faust, 1918) [by monotypy]. Subfamily LEUCERUTHRINAE Goldberger, 1911 Body medium to large; elongate oval. Ventral sucker smaller than oral sucker; near middle ofbody. Testes oblique; pre-ovarian; immediately posterior to ventral sucker. Prostatic sac small.Sinus-organ small, but well defined. Uterine field between ovary and ventral sucker, passingbetween testes. Vitelline follicles in lateral fields, extending almost throughout length of hindbody.Excretory arms unite in forebody. Parasitic in gut of freshwater teleosts and holosteans (in NorthAmerica). LEUCERVTHRUS Marshall & Gilbert, 1905Defined as subfamily.TYPE-SPECIES. Leuceruthrus micropteri Marshall & Gilbert, 1905 [by monotypy]. Family BATHYCOTYLIDAE Dollfus, 1932 Body large; elongate, but stout. Ecsoma absent. Body-surface smooth, but may be wrinkled.Oral and ventral suckers well developed; latter just in anterior half of body. Pharynx welldeveloped. Oesophagus short. 'Driisenmagen' present. Gut-caeca end blindly close to posteriorextremity. Testes two; tandem; separated by ovary; in mid-hindbody. Seminal vesicle thin-walled;tubular; convoluted; small; well forward in forebody. Pars prostatica tubular; indistinct. Sinus-organ and sinus-sac absent. Genital atrium small, but deep. Genital pore mid-ventral close toposterior margin of oral sucker. Ovary oval to reniform; inter-testicular. Mehlis' gland posterioror lateral to ovary. Laurer's canal [see below] and uterine seminal receptacle present. Juel's organand canalicular or blind seminal receptacle absent. Uterus fills much of hind- and forebody. Eggsnumerous; small; non-filamented. Vitellarium several filamentous tubules in hindbody. Excretoryvesicle Y-shaped; arms united in forebody. Parasitic on gills (? or in stomach) of pelagic marineteleosts (scombrids and Coryphaend). BATHYCOTYLE Darr, 1902 [n(w,s)] Defined as family.TYPE-SPECIES. Bathycotyle branchialis Darr, 1902 [by monotypy]. COMMENT. Although Yamaguti (19380) states: 'Laurer's canal apparently without externalopening', when describing Bathycotyle coryphaenae Yamaguti, 1938, it is obvious that a dorsalpore does occur in the type-species, as Dollfus (1932) clearly illustrated it in his figure 5. Yama-guti, however, in contrast to Dollfus, apparently failed to section his material. Family BUNOCOTYLIDAE Dollfus, 1950 Body usually small; fusiform to elongate. Distinct ecsoma absent, but vestige may remain. Body-surface smooth or with plications. Ridges around body often present at level of oral sucker andposterior margin of ventral sucker. Ventral sucker normally inside anterior half of worm. Pharynxwell developed. Oesophagus normally short. 'Driisenmagen' normally present. Gut-caeca nor-mally end blindly near posterior extremity or occasionally form cyclocoel. Testes two; pre-ovarian in hindbody; tandem to symmetrical. Seminal vesicle saccular or tubular; in fore- orhindbody. Pars prostatica tubular or vesicular; short or long; may extend into hindbody.Ejaculatory duct long, short or apparently absent. Sinus-sac usually present, occasionally absent.Hermaphroditic duct present; within sinus-sac when latter present. Permanent sinus-organ THE HEMIUROIDEA 63 normally absent, but temporary sinus-organ may form. Genital atrium small or absent. Ovaryoval; rarely bilobed; between testes and vitellarium. Mehlis' gland post-ovarian. Laurer's canaland canalicular seminal receptacle absent. Juel's organ and uterine seminal receptacle present orabsent. Blind seminal receptacle present or absent. Uterus normally almost entirely in hindbody;mainly pre- to mainly post-ovarian. Eggs numerous; small; without filaments. Vitellarium oneor two, occasionally three, entire (rarely slightly lobed) masses; posterior or postero-lateral toovary. Excretory arms rarely fail to unite in forebody; stem of excretory vesicle often withterminal bulb or with large pore (actual pore may be withdrawn within vestige of ecsoma).Parasitic mainly in stomach of marine teleosts. Key to Bunocotylidae 1. A. Uterine seminal receptacle present; vitellarium 1 or 2 masses ..... 2B. Blind seminal receptacle present; body-surface smooth; vitellarium 2 or 3 masses OPISTHADENINAE (p. 66) 2. A. Parasites up to 6mm in length; large concentration of uterine coils between ovary and testes . . . THELETRINAE (p. 69) B. Parasites small, rarely more than 2 mm in length, commonly less than 1 mm; large concen-tration of uterine coils not present between ovary and testes ..... 3 3. A. Body-surface smooth; ridges present around body at level of oral sucker and posterior margin of ventral sucker; major part of uterine field pre-ovarian; vitellarium single BUNOCOTYLINAE (p. 63) B. Body-surface usually plicated, occasionally smooth; ridges around body at level of suckerabsent; large or major part of uterine field post-ovarian; vitellarium single or double APHANURINAE (p. 64) Subfamily BUNOCOTYLINAE Dollfus, 1950 Body small. Vestige of ecsoma may be present. Body-surface smooth. Ridges present aroundbody at level of oral sucker and posterior margin of ventral sucker; additional ridge often presentclose to posterior extremity. Transverse septate partitions of body may occur. Gut-caeca endblindly or form cyclocoel. Testes tandem to oblique; not separated from ovary by large concen-tration of uterine coils. Seminal vesicle saccular; oval to elongate; in forebody or dorsal to ventralsucker. Pars prostatica short; tubular or vesicular. Sinus-sac absent or small and tubular to oval.Short hermaphroditic duct may extend to form temporary sinus-organ. Genital atrium absent orsmall. Ovary oval. Uterine seminal receptacle present (?). Juel's organ not reported. Blind seminalreceptacle absent. Vitellarium a single, unlobed mass; immediately post-ovarian. Excretoryvesicle expanded distally; arms united in forebody; pore wide. Parasitic in gut of freshwater andeuryhaline teleosts; occasionally progenetic in snails and copepods. COMMENT. According to the literature, the type of seminal storage apparatus occurring in thissubfamily is a matter of some disagreement. Manter (1969a) observed a uterine seminal receptaclein Saturnius segmentatus Manter, 1969, whereas Yamaguti (1970) described a seminal receptaclein S. mugilis (Yamaguti, 1970). Overstreet (1977), when re-defining Saturnius, stated that a seminalreceptacle was absent. No seminal storage apparatus has been described for Bunocotyle cingulataOdhner, 1928, by Odhner (19286) or for B. progenetica (Markowski, 1936) by Deblock (1975).We have examined sections of a paratype specimen of Saturnius papernai Overstreet 1977, andconfirm that: (1) a distinct seminal receptacle (canalicular or blind) and Laurer's canal areabsent; and (2) spermatozoa are present in the proximal region of the uterus, which thus functionsas a uterine seminal receptacle. We could not for certain distinguish Juel's organ, but it is possiblethat in the small species which constitute this subfamily, this structure is reduced or lost altogether.It is conceivable that the transverse ridge around the posterior extremity in some species ofthis subfamily, and possibly both the ampullaceous nature of the distal region of the stem of theexcretory vesicle and the wide excretory pore, represent vestiges of an ecsoma. Overstreet (1977)has described the former as a possible small ecsoma in S. maurepasi Overstreet, 1977, where, inthe living worm, it may be partly withdrawn. 64 D. I. GIBSON & R. A. BRAY Key to Bunocotylinae 1. A. Transverse fibrous septa in fore- and hindbody; cyclocoel absent; sinus-sac present; parasitic in euryhaline teleosts (Mugil) SATURNIUS B. Transverse septa not present; cyclocoel present; sinus-sac absent; parasitic in freshwater or euryhaline teleosts, or progenetic in snails and copepods . . BUNOCOTYLE BUNOCOTYLE Odhner, 1928 Transverse fibrous septa absent. Cyclocoel present. Sinus-sac absent. Uterine seminal recep-tacle (?) presumed to be present. Parasitic in gut of freshwater or euryhaline teleosts, or progeneticin snails and copepods. TYPE-SPECIES. Bunocotyle cingulata Odhner, 1928 [by original designation].COMMENT. See Theletrum for comment on B. sudatlantica Parukhin, 1976. SATURNIUS Manter, 1969 [n(w,s)] Small papillae or corrugations may be associated with suckers. Internal transverse, fibrous septapresent in fore- and hindbody. Gut-caeca end blindly. Sinus-sac may contain ejaculatory (? herma-phroditic) vesicle. Parasitic in, and under lining of, stomach of euryhaline teleosts (Mugilcephalus). TYPE-SPECIES. Saturnius segmentatus Manter, 1969 [by original designation]. COMMENT. This genus has recently been revised by Overstreet (1977), who has cleared up manyof the discrepancies between the descriptions of S. segmentatus and S. mugilis (Yamaguti, 1970). Subfamily APHANURINAE Skrjabin & Guschanskaja, 1954 [28.4.1954]Ahemiurinae Chauhan, 1954 [17.11.1954] Body normally small. Vestige of ecsoma may be present. Body-surface usually with distinctannular plications, occasionally ( ?) smooth [some species of Aphanums]. Ridges around body atlevel of suckers absent. Gut-caeca end blindly near posterior extremity. Testes tandem to sym-metrical; normally well posterior to ventral sucker; not separated from ovary by large concentra-tion of uterine coils. Seminal vesicle tubular in forebody, or saccular (oval, elongate or bipartite)in hindbody (or at least posterior to middle of ventral sucker). Pars prostatica tubular or vesicular;short or long. Ejaculatory duct long, short or apparently absent. Sinus-sac present, enclosinghermaphroditic duct, or (?) absent. Ovary oval; immediately or almost immediately post-testicular. Blind seminal receptacle absent. Uterine seminal receptacle and ( ?) JueFs organpresent. Large or major part of uterine field post-ovarian. Vitellarium one or two compactmasses; usually immediately posterior, occasionally lateral, to ovary. Excretory arms united inforebody; excretory pore often large; actual pore may be withdrawn within vestige of ecsoma.Parasitic mainly in stomach or oesophagus of marine teleosts. COMMENT. A small 'seminal receptacle' has been reported for Duosphincter by Yamaguti (1970)and in some species of Aphanurus. A uterine seminal receptacle has been reported for Myosacciumand other species of Aphanurus. It is likely that the reports of a 'seminal receptacle' from thisgroup are mistaken, as Juel's organ and a uterine seminal receptacle are easily mistaken for sucha structure in whole-mount preparations. The genera of this group are essentially typical hemiurids which have lost their ecsoma. Thepresence of records from the oesophagus suggests that these parasites may inhabit the less acidicanterior regions of the stomach, and do not have the same requirement for an ecsoma as theclosely related forms which tend to inhabit the pyloric region of the stomach. THE HEMIUROIDEA 65 Key to Aphanurinae 1. A. Vitellarium composed of 2 distinct masses ..... 2B. Vitellarium composed of 1 distinct mass ....... APHANURUS 2. A. Seminal vesicle tubular, winding in forebody ..... DUOSPHINCTERB. Seminal vesicle saccular (oval, elongate or bipartite; often attenuated anteriorly), posterior to middle of ventral sucker .......... 3 3. A. Pars prostatica vesicular, with muscular wall MYOSACCIUM B. Pars prostatica tubular ........... 4 4. A. Seminal vesicle oval ; sinus-sac present ....... AHEMIURUS B. Seminal vesicle apparently bipartite and attenuated anteriorly; sinus-sac apparently absent APHANUROIDES APHANURUS Looss, 1907 [n(w)] Chauhanurus Skrjabin & Guschanskaja, 1954Helaphanurus Slusarski, 1957 Body-surface normally plicated, occasionally ( ?) smooth. Testes oblique, occasionally symmetricalor tandem. Seminal vesicle oval to elongate oval; in hindbody; wall may be muscular. Parsprostatica tubular; long. Ejaculatory duct long or short. Sinus-sac present; tubular. Temporarysinus-organ sometimes present as small cone. Vitellarium a single, large, entire or slightly in-dented, post-ovarian mass. Parasitic in oesophagus and stomach of essentially marine teleostsfrom marine and brackish water environments. TYPE-SPECIES. Aphanurus stossichi (Monticelli, 1891) [by original designation]. COMMENT. There has been considerable comment in the literature (Looss, 1908; Rioja, 1923;Chauhan, 1954; Slusarski, 1957) as to whether Aphanurus possesses or lacks a small vestigialecsoma. Although this question has not been resolved, Chauhan (1954) suggested that the con-fusion may have been caused by the bulbous nature of the excretory vesicle. The possible vestigesof an ecsoma, however, may be a common feature of both the aphanurines and the bunocotylines.Some species of Aphanurus (A. caesionis Yamaguti, 1952 and A. dorosomatis Yamaguti, 1953)are reported to have a smooth body-surface; but, as they are known from only one or twospecimens, this requires confirmation. If this is proved to be correct, then there may be groundsfor distinguishing them from the other species of Aphanurus at the generic level. AHEMIURUS Chauhan, 1954 Testes symmetrical to oblique. Seminal vesicle oval; in hindbody. Pars prostatica tubular; long.Ejaculatory duct long. Sinus-sac present; elongate oval. Vitellarium two oval, compact masses;symmetrical; post-ovarian. Parasitic in stomach of marine teleosts. TYPE-SPECIES. Ahemiurus karachii (Srivastava, 1937) [by original designation]. COMMENT. Yamaguti (1971) lists Ahemiurus as a synonym of Opisthadena despite the fact thatChauhan (1954) emphasized the presence of cuticular plications in this species. The latter is afeature which occurs only in hemiurid and aphanurine genera. Although the seminal storageapparatus of the genus has not been described, we expect it to conform to the subfamily definition. (?) APHANUROIDES Nagaty & Abdel-Aal, 1962 [Inadequately described.] Testes tandem. Seminal vesicle saccular; ( ?)bipartite ; attenuatedanteriorly; extending between anterior testis and posterior half of ventral sucker. Pars prostaticatubular. [Terminal genitalia not described in detail.] Sinus-sac (?) absent. Short hermaphroditicduct and genital atrium apparently present. [Figures of Nagaty & Abdel-Aal, 1962, suggest thattemporary sinus-organ may form (?).] Vitellarium two compact masses; symmetrical to oblique;post-ovarian. Excretory arms (?). Parasitic in gut of marine teleosts. 66 D. I. GIBSON & R. A. BRAY TYPE-SPECIES: Aphanuroides lethrini Nagaty & Abdel-Aal, 1962 [by original designation]. DUOSPHINCTER Manter & Pritchard, 1960 Strongly developed sphincter muscles surround apertures of suckers. Testes oblique to tandem.Seminal vesicle tubular; winding in forebody. Pars prostatica tubular; short. Sinus-sac small;oval. Temporary sinus-organ may form. [Small seminal receptacle (? Juel's organ) present,according to Yamaguti, 1970.] Vitellarium two oval masses; oblique to tandem; immediatelypost-ovarian. Parasitic in stomach of marine teleosts. TYPE-SPECIES. Duosphincter zancli Manter & Pritchard, 1960 [by monotypy]. MYOSACCIUM Montgomery, 1957Neogenolinea Siddiqi & Cable, 1960. Testes symmetrical to tandem. Seminal vesicle saccular; attenuated anteriorly; at level of posteriormargin of ventral sucker. Pars prostatica vesicular; with strong, muscular wall; in forebody.[Terminal genitalia confused in literature.] Sinus-sac apparently tubular; enclosing hermaphrodi-tic duct, which may form temporary sinus-organ. Eggs without filament [the structure of collapsedeggs may apparently give the impression that a short filament and spine are present (?)]. Vitel-larium two oval or slightly indented masses; oblique to tandem; one mass usually lateral, otherimmediately postero-lateral or posterior, to ovary. Parasitic in stomach of marine teleosts(Clupeidae). TYPE-SPECIES. Myosaccium ecaude Montgomery, 1957 [by original designation]. COMMENT. There appears to be some difference of opinion with regard to the presence or absenceof filaments on the eggs. Montgomery (1957) and Kohn & Buhrnheim (1964) indicate that afilament is present with, in the case of the latter authors, an additional small spine at the oppositeend of the egg. Overstreet (1969) and Yamaguti (1971), after examining some of Montgomery'stype-specimens, state that filaments on the egg could not be seen. Overstreet suggests that theso-called filaments described in this genus may be an artifact present in collapsed eggs. Subfamily OPISTHADENINAE Yamaguti, 1970Intuscirrinae Skrjabin & Guschanskaja, 1959 Body spindle-shaped to elongate. Body-surface smooth. Transverse ridges in body-wall presentor absent around body at level of oral sucker and/or posterior margin of ventral sucker [theseare often not obvious]. Presomatic pit reported (?) in Mitrostoma. Gut-caeca end blindly nearposterior extremity. Testes tandem to oblique; usually well posterior to ventral sucker and nearovary; not separated from ovary by large concentration of uterine coils. Seminal vesicle tubularto saccular (? rarely bipartite); in fore- or hindbody. Pars prostatica long or short; tubular orvesicular. Ejaculatory duct long to short or apparently absent. Sinus-sac present; oval to elongateoval; enclosing hermaphroditic duct. Sinus-organ (? temporary) occasionally present. Genitalatrium usually present; small. Ovary normally oval, occasionally bilobed; normally close totestes. Blind seminal receptacle present; large; usually dorsal or antero-dorsal to ovary. Juel'sorgan and uterine seminal receptacle absent. Uterus mainly pre- to mainly post-ovarian. Vitel-larium two, occasionally three, entire or slightly indented masses; posterior or postero-lateral toovary. Excretory arms usually, but not always, united in forebody. Parasitic in stomach, occasion-ally intestine, of marine teleosts. COMMENT. The presence of ridges (tegumental folds) around the body, especially the one im-mediately posterior to the ventral sucker, may well be a good generic criterion. We are con-cerned about the significance of this feature, as it is often very difficult to see, and in genera suchas Genolinea, where it is known to occur, it has only been reported occasionally. THE HEMIUROIDEA 67 Key to Opisthadeninae 1. A. Seminal vesicle entirely in hindbody . ......... 2 B. Seminal vesicle in forebody (occasionally dorsal or postero-dorsal to ventral sucker) . 3 2. A. Ejaculatory duct short or absent; pars prostatica reaches forward to level of caecal bifurca- tion; (?) presomatic pit apparently present ...... MITROSTOMA B. Ejaculatory duct long; pars prostatica does not reach further forward than ventral sucker; presomatic pit absent OPISTHADENA 3. A. Vitellarium 2 symmetrical, oblique or tandem masses ..... GENOLINEAB. Vitellarium 3 masses, the anterior pair being symmetrical and the posterior mass being the largest NEOTHELETRUM OPISTHADENA Linton, 1910 Body elongate. Transverse ridge (fold) of body-wall around body immediately posterior toventral sucker. Testes tandem; posterior to middle of body. Seminal vesicle in hindbody; usuallytubular and sinuous, but reported as enclosed within muscular, ovoid sac ['seminal sac' ofManter, 1947] or as being saccular. Pars prostatica tubular; not reaching further forward thanposterior margin of ventral sucker. Ejaculatory duct long. Sinus-sac oval. Hermaphroditic ductmay be sub-divided. Sinus-organ apparently present as small cone, at least temporarily. Ovaryclose to testes. Uterus mainly pre-ovarian. Vitellarium two symmetrical to oblique masses; post-ovarian. Excretory arms diverticulate; united in forebody. Parasitic in stomach of marine teleosts(especially Kyphosus}. TYPE-SPECIES. Opisthadena dimidia Linton, 1910 [by original designation]. GENOLINEA Manter, 1925 [t(w,s); n(w,s)] Parasterrhurus Manter, 1934Intuscirrus Acena, 1947Pseudobunocotyla Yamaguti, 1965 Body spindle-shaped to slightly elongate. Transverse ridge usually present around body immedia-tely posterior to ventral sucker (often inconspicuous and frequently not reported); similar ridgemay surround oral sucker. Large pre-oral lobe may be present. Ventral sucker normally inanterior half of body, (?) occasionally near middle; sphincter muscles sometimes present aroundaperture. Testes tandem to oblique; close to ovary. Seminal vesicle small; tubular; convoluted inforebody, occasionally dorsal or postero-dorsal to ventral sucker. Pars prostatica tubular tovesicular; short. Ejaculatory duct short or absent. Sinus-sac oval to elongate oval; small. Sinus-organ occasionally present (? temporary). Ovary near middle of hindbody. Uterus usually in bothpre- and post-ovarian fields, occasionally post-vitelline distribution is limited. Metraterm reportedin some instances to be spinous (?). Vitellarium two compact (occasionally lobed), symmetrical,oblique or tandem masses; posterior or postero-lateral to ovary. Excretory arms united in fore-body. Parasitic mainly in stomach of marine teleosts. TYPE-SPECIES. Genolinea lalicauda Manter, 1925 [by original designation]. COMMENT. The position of the ventral sucker near the middle of the body in G. dactylopagriManter, 1954, is much further posterior than normally occurs in this family. The morphologyof this species suggests that it is related to Lewodera Linton, 1910, as Manter (1954) initiallybelieved, and both are recorded from related percoid families of teleosts. MITROSTOMA Manter, 1954 Body elongate. Thickened projection present on each side of body at level of posterior margin ofventral sucker. Nipple-shaped protuberance (? vestige of ecsoma) may be present at posteriorextremity. Weakly muscled pre-oral lobe bears mouth. Structure resembling (?) presomatic pitapparently present anterior to ventral sucker. Ventral sucker with 'sphincter muscles in anteriorand posterior halves'. Testes tandem; close to ovary; near middle of hindbody. Seminal vesicle 68 D. I. GIBSON & R. A. BRAY tubular; convoluted; entirely in hindbody. Pars prostatica tubular; reaches forward to caecalbifurcation. Ejaculatory duct short or absent. Sinus-sac short; pyriform; (?) protrusible. Ovaryin posterior half of hindbody. Uterus mainly pre-ovarian, but does extend into post-vitellineregion. Vitellarium two oblique to symmetrical, post-ovarian masses. Excretory arms united inforebody. Parasitic in intestine of marine teleosts. TYPE-SPECIES. Mitrostoma nototheniae Manter, 1954 [by original designation]. COMMENT. There are several features of the genus Mitrostoma, such as the overall arrangement ofthe organs, the apparent presence of a presomatic pit and the reported presence of a nipple-shapedprotuberance at the posterior extremity of one specimen, which suggests that it might be a hemiuridwith a lost or vestigial ecsoma, no longer required because of its intestinal habitat. Manter (1954),however, reported that a blind seminal receptacle was present. The presence of this type ofseminal receptacle, as opposed to a uterine seminal receptacle, and the great morphologicalsimilarity between this parasite and Genolinea bower si (Leiper & Atkinson, 1914), reported fromrelated nototheniid hosts (Prudhoe & Bray, 1973), indicate that its position within the Opistha-deninae is probably correct. NEOTHELETRUM gen. nov. Body small; elongate to spindle-shaped. Tegumental fold around body posterior to ventral suckerapparently absent. Body-surface smooth. Ventral sucker in anterior half of body. Pre-pharynxabsent. Pharynx well developed. Oesophagus short; often with small diverticulum. Gut-caeca endblindly near posterior extremity. Testes 2; oval; oblique to symmetrical; usually separated fromventral sucker by loops of uterus; occasionally sandwiched between ventral sucker and ovary.Seminal vesicle small ; tubular to saccular ( ? occasionally bipartite) ; in forebody. Pars prostaticashort; tubular to vesicular. Ejaculatory duct short or absent. Sinus-sac small; oval. Small tem-porary sinus-organ may form. Hermaphroditic duct short; formed within sinus-sac. Genitalatrium small. Genital pore mid-ventral in forebody. Ovary oval (may occasionally be bilobed);post-testicular; near middle of hindbody. Blind seminal receptacle antero-dorsal to ovary.Laurer's canal, Juel's organ and both canalicular and uterine seminal receptacle presumablyabsent. Uterus almost entirely in hindbody; usually with roughly equal amounts in pre- and post-ovarian fields; occasionally with majority of uterus in post-ovarian field. Eggs small; numerous;without filaments. Vitellarium three compact, entire or slightly indented masses; anterior pairsymmetrical, connected by narrow isthmus; posterior mass larger, may be slightly bilobed[vitellarium is essentially two tandem masses, the anterior of which is divided into two distinctlobes: the vitellarium may appear as two tandem masses in lateral view]; post-ovarian. Excretoryarms united in forebody or not. Parasitic in stomach of marine teleosts. TYPE-SPECIES. Neotheletrum lissosomum (Manter, 1940) n. comb. COMMENT. Neotheletrum differs from Theletrum in that: (1) a blind rather than a uterine seminalreceptacle is present; (2) much of the uterus is post-ovarian rather than being between the ovaryand testes; (3) the anterior vitelline mass is consistently divided into two; and (4) the tegumentalridge around the body immediately posterior to the ventral sucker is absent.The additional species which we include in this genus are as follows : N. frontilatum (Manter, 1969) n. comb. N. gravidum (Manter, 1940) n. comb. N. magnasaccum (Sogandares-Bernal & Sogandares, 1961) n. comb, [possibly a synonymof N. lissosomum]. N. pomacentri (Nahhas & Cable, 1964) n. comb. N. frontilatum, which Yamaguti (1971) considers to belong to Hysterolecithoides, differs from theother species of Neotheletrum in that the uterus is almost entirely post-ovarian, the testes areclose behind the ventral sucker and close to the ovary, and the excretory arms are not united inthe forebody. On these grounds a case could be made for erecting a new genus for this species;but we have included it in Neotheletrum as there seems little point in further sub-division atpresent. THE HEMIUROIDEA 69 THELETRINAE subfam. nov. Body elongate. Ecsoma absent. Body-surface smooth ; papillae may be present ventrally in fore-or hindbody; transverse ridge may be present around body near posterior margin of ventralsucker and possibly around oral sucker. Oral and ventral suckers well developed ; ventral suckerin anterior half of body. Prepharynx absent. Pharynx well developed. Oesophagus short. Gut-caeca end blindly near posterior extremity, (?) or at level of ovary. Testes two; pre-ovarian;tandem to oblique; near middle of hindbody; separated from ovary by majority or large part ofuterine coils. Seminal vesicle tubular or (?) saccular; in forebody, but sometimes reaching back toposterior margin of ventral sucker. Pars prostatica short; tubular or slightly vesicular. Ejaculatoryduct short or apparently absent. Sinus-sac usually small; oval or elongate oval; weakly developed;enclosing hermaphroditic duct; may extrude slightly through genital pore. Permanent sinus-organ absent (?), but temporary sinus-organ may form. Genital atrium small or absent. Ovaryoval ; near posterior extremity or at least well inside posterior half of hindbody. Laurer's canaland both canalicular or blind seminal receptacle absent [Laurer's canal reported present (?) inIndoderogenes], Uterine seminal receptacle present. Juel's organ assumed to be present. Uterusalmost entirely or mainly in hindbody (small part of uterus is coiled in forebody of Monoleci-thotremd) ; mainly pre-ovarian, with large proportion of uterine coils between ovary and testes.Eggs numerous; small; without filaments. Vitellarium one entire or two tandem to oblique, entireor slightly lobed masses ; posterior or postero-lateral to ovary. Excretory vesicle Y-shaped ; armsunited in forebody. Parasitic normally in stomach of marine teleosts. COMMENT. This subfamily is erected for forms which resemble the Opisthadeninae; but lack ablind seminal receptacle, possess a uterine seminal receptacle (plus presumably Juel's organ) andcontain a large concentration of uterine coils between the ovary and testes. The position ofIndoderogenes Srivastava, 1937, discussed below, is problematical; but in gross morphology itdoes appear to key satisfactorily to this subfamily. The sinus-sac in both Theletrum and Monolecithotrema often appears to be slightly extrudedthrough the genital pore. It is not clear from our observations of the type-species if this is infact so, or whether a temporary sinus-organ is formed by an eversion of the hermaphroditic duct. Key to Theletrinae 1 . A. Vitellarium single (great care should be taken with this observation, as at certain angles the vitellarium of Theletrum appears to be single); transverse ridge posterior to ventralsucker absent; some uterine coils in forebody . . . . MONOLECITHOTREMAB. Vitellarium double; uterus not coiled in forebody ....... 2 2. A. Seminal vesicle tubular; transverse ridge normally present posterior to ventral sucker; gut-caeca terminate near posterior extremity ...... THELETRUM B. Seminal vesicle saccular; transverse ridge posterior to ventral sucker not reported; gut-caeca apparently terminate at level of anterior margin of ovary. . INDODEROGENES THELETR UM Linton, 1910 [t( w)] Transverse tegumental ridge present around body immediately posterior to ventral sucker andpossibly around oral sucker. Papillae may be present ventrally in hindbody. Gut-caeca terminateat posterior extremity. Testes fairly close together, but separated by uterus. Seminal vesicletubular. Pars prostatica slightly vesicular. Sinus-sac elongate oval; thin-walled; sheath-like; maybe partly extruded through genital pore. Ovary close to posterior extremity. Uterine coils en-tirely or almost entirely in hindbody; few or no coils posterior to vitellarium. Vitellarium twooblique, entire or slightly lobed masses; close together; posterior or postero-lateral to ovary;at posterior extremity of body. Parasitic in stomach (occasionally intestine) of marine teleosts. TYPE-SPECIES. Theletrum fust if orme Linton, 1910 [by original designation]. COMMENT. We agree with Yamaguti (1971) that this genus is monospecific. We do not agree,however, that the remainder of the species allocated to this genus should be placed in GenolineaManter, 1925, and have, therefore, erected a new genus, Neotheletrum, in the Opisthadeninae to 70 D. I. GIBSON & R. A. BRAY accommodate them (see p. 68). Our observations of the type-species confirm that a uterineseminal receptacle is present as indicated by Yamaguti's (1971) and possibly Vigueras' (1958)figures. Bunocotyle sudatlantica Parukhin, 1976, may belong to this genus, as it possesses manymorphological similarities and is recorded from the same family of host (Chaetodontidae).Parukhin's (19760) description, however, indicates that there is a single vitelline mass and acyclocoel present. Nevertheless, when viewed from certain angles T. just if or me can appear topossess only one vitelline mass, and the presence or absence of a cyclocoel is often difficult toascertain in this family. Certainly, Parukhin's material does not fit within our concept ofBunocotyle. (^INDODEROGENES Srivastava, 1937 Transverse ridge around body posterior to ventral sucker apparently absent. Gut-caeca terminateclose to anterior margin of ovary. Testes separated by uterine coils. Seminal vesicle saccular(flask-shaped). Pars prostatica tubular. Sinus-sac (?) absent. Hermaphroditic duct short. Sinus-organ small ( ? temporary). Genital atrium small. Ovary close to posterior extremity. Laurer'scanal reported present (?). Uterine coils entirely or almost entirely in hindbody; entirely oralmost entirely pre-ovarian. Vitellarium two tandem to oblique masses; posterior or postero-lateral to ovary ; at posterior extremity of body. Parasitic in stomach of marine teleosts. TYPE-SPECIES. Indoderogenes purii Srivastava, 1937 [by monotypy]. COMMENT. This genus, initially defined in an abstract by Srivastava (19376) and later (1941) des-cribed in more detail, is known from only three specimens. In gross morphology it appearssimilar to the other two genera of this subfamily, although Srivastava (1941) reported the presenceof Laurer's canal. We have some doubts about this, as such an observation on whole-mounts witha large, dense uterine field, as his figure indicates, must be questionable. Despite the fact that nomention was made by Srivastava of the presence of a sinus-sac, there may have been one present,as this structure is either small or weakly developed in the other genera of this subfamily. If Laurer's canal is proved to be present by future workers, this genus should be transferred tothe Halipeginae Poche, 1926, where, although sharing some of its features with DeropegusMcCauley & Pratt, 1961, its gross morphology does not conform to the normal derogenid pattern.In addition, unlike the majority of halipegines this genus was recorded from a marine teleost,although the locality of the record, an almost land-locked bay in the Bay of Bengal, is brackishat certain times of the year. MONOLECITHOTREMA Yamaguti, 1970 [T(w)] Transverse ridges around body absent. Papillae may be present ventrally in forebody. Gut-caecaterminate blindly at posterior extremity. Testes close together, but sometimes separated by uterus.Seminal vesicle tubular ; usually extending back dorsally to ventral sucker. Pars prostatica tubular;poorly developed ; linked to seminal vesicle by aglandular duct. Sinus-sac small ; poorly developed ;may be slightly extruded through genital pore. Ovary well inside posterior half of hindbody.Small proportion of uterus may be coiled in forebody; small part of uterus extends posteriorly tovitellarium. Vitellarium one large, entire mass; immediately post-ovarian. Parasitic in stomachof marine teleosts. TYPE-SPECIES. Monolecithotrema kala Yamaguti, 1970 [by original designation]. COMMENT. Examination of 14 paratype-specimens mounted on a single slide shows that a uterineseminal receptacle is present, and that Yamaguti was probably mistaken in his observation of asmall seminal receptacle between the ovary and the vitellarium. This structure corresponds withthe position of Mehlis' gland, but might also have been part of the uterine seminal receptacle,JuePs organ (until sectioned material is examined we are assuming that this is present) or even adiverticulum of the gut-caeca. As in Theletrum, the uterine seminal receptacle tends to extendposteriorly to the vitellarium. THE HEMIUROIDEA 71 Family DEROGENIDAE Nicoll, 1910 Halipegidae Poche, 1926Liocercidae Ejsmont, 1931 Body normally small; usually spindle-shaped to elongate oval. Ecsoma absent. Body-surfacesmooth. Oral and ventral suckers well developed; ventral sucker usually near middle of body,occasionally more anterior or posterior. Pharynx well developed. Oesophagus short. 'Driisen-magen' usually present. Gut-caeca end blindly or form cyclocoel. Testes two; symmetrical totandem; pre- or post-ovarian; in hindbody. Seminal vesicle thin- walled; oval, elongate or tubular;not constricted into portions; in forebody; occasionally partly or wholly enclosed within sinus-sac. Pars prostatica usually tubular, occasionally vesicular; occasionally enclosed within sinus-sac. Ejaculatory duct short or absent; often within sinus-sac. Sinus-sac normally present, occasion-ally absent ; usually small and oval ; often weakly developed ; may enclose all or part of parsprostatica and seminal vesicle. Permanent sinus-organ present as small cone or absent. Herma-phroditic duct normally present; occasionally absent; usually short. Genital atrium present orabsent; usually small. Genital pore mid-ventral in forebody. Ovary oval; pre- or post-testicular.Mehlis' gland normally post-ovarian or occasionally at level of ovary. Seminal storage and dis-posal apparatus variable. Laurer's canal usually present; either opening dorsally to exterior orleading into Juel's organ ; often dilated proximally to form small rudimentary seminal receptacle,which is occasionally enlarged to form an apparently functional canalicular seminal receptacle.Juel's organ absent or present in either rudimentary or fully-developed state. Blind seminalreceptacle present rarely. Uterine seminal receptacle normally present; rarely absent. Uterus mayor may not extend posterior to vitellarium ; significant proportion of uterus usually coiled inforebody. Eggs numerous; with or without filaments or threads; rarely with anopercular spine.Vitellarium one or two masses ; entire or lobed (lobes normally shallow, rarely digitate) ; pre- orpost-ovarian; symmetrical, oblique or tandem. Excretory vesicle Y-shaped; arms united in fore-body. Parasitic usually in gut (normally stomach) of freshwater and marine teleosts, but occasion-ally recorded from amphibians, reptiles and freshwater shrimps. COMMENT. This is a family which does not have a constant seminal storage and disposal apparatusin the female system. As discussed below (p. 124), the variations of this apparatus probably occurbecause they are a diverse and successful, but relatively primitive group, which appear to haveevolved at about the time when the first modifications of the primitive arrangement of the seminalstorage and disposal apparatus began to occur. The variety of conditions found in this group tendto parallel those which have occurred during the evolution of some of the more advanced hemi-uroids, such as the hemiurids, bunocotylids and lecithasterids. Key to Derogenidae 1 . A. Testes posterior to ovary and vitellarium GONOCERCINAE (p. 74) B. Testes anterior to ovary and vitellarium ......... 2 2. A. Parasites primarily of freshwater teleosts, but occasionally present in brackish water or marine teleosts close to the ancient Sarmatic Sea region [Caspian. Black and Mediterra-nean Seas], in amphibians, in reptiles and in freshwater shrimps; ventral suckeroccasionally anterior to middle of body; uterus not present posterior to vitellarium;sinus-sac, when present, may enclose part of or entire seminal vesicle and/or pars prostatica HALIPEGINAE (p. 75) B. Parasitic in marine teleosts ; ventral sucker not present in anterior half of body ; uterus oftenextends posterior to vitellarium; sinus-sac present, never enclosing any part of parsprostatica or seminal vesicle DEROGENINAE (p. 71) Subfamily DEROGENINAE Nicoll, 1910 (?) Liopyginae Ejsmont, 1931(?) Liocercinae Ejsmont, 1931Genarchinae Skrjabin & Guschanskaja, 1955Orthoruberinae Nasir & Gomez, 1977 72 D. I. GIBSON & R. A. BRAY Ventral sucker in middle or posterior to middle of body. Gut-caeca end blindly or form cyclocoel.Testes pre-ovarian; symmetrical to oblique. Seminal vesicle small; globular to tubular. Parsprostatica usually tubular, occasionally vesicular; short or long. Sinus-sac present; globular tocylindrical. Permanent sinus-organ present; small; cone-shaped. Hermaphroditic duct normallyshort. Genital atrium small; often filled by sinus-organ. Ovary close behind testes. Laurer's canalpresent or absent; opening dorsally or into rudimentary Juel's organ; may be dilated proximallyforming large rudimentary or functional canalicular seminal receptacle. Blind seminal receptaclepresent when Laurer's canal and uterine seminal receptacle absent; latter usually present. Uteruscoiled throughout hindbody and part of forebody; significant proportion of uterus often presentposterior to vitellarium. Eggs without filaments or threads, but may have anopercular spine.Vitellarium two symmetrical to tandem, oval or slightly indented masses ; posterior or occasionallylateral and postero-lateral to ovary. Parasitic in gut (mainly stomach) of marine teleosts. Key to Derogeninae 1. A. Uterus not normally extending posterior to vitellarium ...... 4 B. Significant proportion of uterus posterior to vitellarium ...... 2 2. A. Cyclocoel present PROGONUS B. Gut-caeca end blindly ............ 3 3. A. Eggs drawn into sharp point at anopercular pole .... DEROGENOIDESB. Eggs lacking point at anopercular pole DEROGENES 4. A. Vitelline masses tandem to oblique, lateral and postero-lateral to ovary; blind seminal receptacle present LEURODERA B. Vitelline masses symmetrical to oblique, post-ovarian; Laurer's canal and presumably uterine seminal receptacle present GONOCERCELLA COMMENT. Initially, we considered Gonocercella and Leurodera to be members of the Halipeginaebecause of the pre-vitelline distribution of the uterus. The fact that they parasitize marine teleostsand the structure of the terminal genitalia, however, clearly associated them with the Derogeninae.It could also be argued that Arnold, Magnibursatus and Tyrrhenia, which are present in teleostsfrom the brackish to marine conditions of the Black and Mediterranean Seas, should be includedin the Derogeninae. The structure of the terminal genitalia, however, is different from that of thelatter group. In addition, these three genera are morphologically related to some of the Asianhalipegines from freshwater and can be historically and zoogeographically related to the hali-pegines of the central Asian region via the ancient Sarmatic Sea. DEROGENES Liihe, 1900 [n(w,s)] (1) Liopyge Looss, 1899(l)Liocerca Looss, 1902 Gut-caeca end blindly near posterior extremity. Testes symmetrical to oblique. Seminal vesicleglobular to tubular and sinuous. Pars prostatica short to long. Sinus-sac globular. Male and femaleducts unite within sinus-organ. Ovary usually close behind testes; may be lateral to posteriortestis when latter is oblique. In D. varicus Laurer's canal opens distally into rudimentary Juel'sorgan and dilates proximally forming large rudimentary seminal receptacle. Uterine seminalreceptacle present. Uterine field usually extends from posterior extremity to region of genitalpore; significant proportion of uterus posterior to vitellarium. Eggs without anopercular spine.Vitelline masses symmetrical to oblique; globular or slightly indented; post-ovarian. Parasitic instomach, oesophagus or occasionally gall-bladder of marine ( ? and freshwater) teleosts. TYPE-SPECIES. Derogenes ruher Liihe, 1900 [by monotypy]. COMMENT. The overall morphology ofLiopyge bonnieri (Monticelli, 1893) is probably identical tothat of Derogenes, if the vitellarium and the testes have been confused. It is difficult to believe,however, that an experienced worker like Monticelli would make such a mistake, especially as heoriginally considered his specimens to be Distoma varicum [now Derogenes varicus (Miiller,1780)], and later re-named them Distoma bonnieri. Monticelli recorded this species from Trig/a THE HEMIUROIDEA 73 gurnardus in the English Channel. Evidence against the validity of the genus Liopyge is that inspite of the abundance of this host it has never been found a second time, although Derogenesvarious has been recorded from the English Channel in Trigla gurnardus by Nicoll (1914) and inT. lucerna by Nicoll (1914), Baylis & Jones (1933) and by ourselves: we have re-checked thedetermination of the last two records. Until there is more conclusive evidence for the existenceof Liopyge, therefore, we are including this genus, and its synonym Liocerca, as questionablesynonyms of Derogenes. The genus Pronopyge Looss, 1 899, has been considered to be a close relative of Liopyge (seeYamaguti, 1971). Its type-species was originally quoted as P. ocreata (Rudolphi, 1802); butFasciola ocreata of Rudolphi (1802) was shown by Odhner (1911) to be a species of Hemiurus,and, as stated by Poche (1926), Pronopyge must be considered a junior synonym of the lattergenus. Monticelli (1891) considered Distoma ventricosum Rudolphi, 1819 (and van Beneden, 1871)[nee D. ventricosum (Pallas, 1774)], and Distomum carolinae Stossich, 1889, to be synonyms ofFasciola ocreata Rudolphi, 1802. Figures of these two species by van Beneden (1871) and Stossich(1889) and of'Apoblema ocreata' by Monticelli (1891) suggest that they belong to the fellodistomidgenus Pseudopentagramma Yamaguti, 1971 (a junior synonym of Pronoprymna Poche, 1926 - seeBray & Gibson, in prep.) and they are similar to figures of Pseudopentagramma symmetrica(Chulkova, 1939) produced by Margolis & Ching (1965). DEROGENOIDES Nicoll, 1913 Gut-caeca end blindly. Testes symmetrical to oblique. Seminal vesicle small; globular. Parsprostatica short. Sinus-sac somewhat cylindrical with proximal end slightly enlarged. Sinus-organ (?) presumably present. Ovary immediately posterior to testes. Laurer's canal and Juel'sorgan (?). Seminal receptacle (? rudimentary) reported. Uterine seminal receptacle (?). Much ofuterus present posterior to vitellarium. Eggs drawn out to sharp point at anopercular pole.Vitelline masses entire; symmetrical; post-ovarian. Parasitic in stomach and intestine of marineteleosts. TYPE-SPECIES. Derogenoides ovacutus Nicoll, 1913 [by original designation]. COMMENT. Derogenoides skrjabini Vlasenko, 1931, was made the type-species of Magnibursatusby Naidenova (1969). D. tetralecithum Roman, 1955, and possibly D. sargi Pogoreltseva, 1954,also appear to be halipegines. GONOCERCELLA Manter, 1940 Ventral sucker in posterior half of body. Gut-caeca end blindly. Testes oblique. Seminal vesicletubular; coiled. Pars prostatica vesicular. Sinus-sac small. Sinus-organ a muscular cone. Ovaryimmediately posterior to testes; close to posterior extremity. Laurer's canal opens dorsally (ac-cording to MacCallum, 1913). Blind or canalicular seminal receptacle absent. Uterine seminalreceptacle presumably present. Juel's organ presumably absent. Uterus mainly coiled in forebody ;not reaching posterior to vitellarium. Eggs without anopercular spine. Vitelline masses entire;symmetrical; post-ovarian; close to posterior extremity. Parasitic in stomach of marine teleosts. TYPE-SPECIES. Gonocercella pacifica Manter, 1940 [by original designation]. LEURODERA Union, 1910 [n(w)] Orthoruberus Nasir & Gomez, 1977 Body oval; stout. Gut-caeca end blindly near posterior extremity. Testes symmetrical; largely orpartly extra-caecal. Seminal vesicle tubular; slightly sinuous. Pars prostatica short; with few tomany external gland-cells ; may be partly tubular and vesicular anteriorly. Sinus-sac oval. Sinus-organ small (well developed and conical in Orthoruberus}. Ovary just posterior to testes; close toposterior extremity. Laurer's canal, Juel's organ and uterine seminal receptacle apparently absent. 74 D. I. GIBSON & R. A. BRAY Blind seminal receptacle present; large; antero-ventral, antero-lateral or antero-dorsal to ovary.Uterus anterior to vitellarium; much of it pre-testicular. Eggs without anopercular spine. Vitellinemasses entire or slightly indented; tandem to oblique; lateral and postero-lateral to ovary.Parasitic in gut (mainly stomach) of marine teleosts (especially Pomadasyidae). TYPE-SPECIES. Leurodera decora Linton, 1910 [by original designation]. COMMENT. Leurodera ocyri Travassos, Teixeira de Freitas & Blihrnheim, 1965, and L. inaequalisTravassos, Teixeira de Freitas & Buhrnheim, 1966, are not, in our opinion, specimens of Leurodera.The descriptions appear to resemble Lecithophyllum and Aponurus, and Overstreet (1973) con-sidered these two species to be synonyms of Aponurus pyriformis (Linton, 1910). PROGONUS Looss, 1899 [t(w,s)] Genarches Looss, 1902 Cyclocoel present. Testes symmetrical. Seminal vesicle elongate, spindle-shaped, elongate oval orglobular. Pars prostatica short; slightly vesicular. Sinus-sac small; globular. Ovary sinistral; half-way between testes and posterior extremity. Canalicular seminal receptacle present. Laurer'scanal ends blindly after passing dorsally through cyclocoel. Rudimentary JueFs organ present assmall dilations of Laurer's canal at distal extremity and especially at junction with seminalreceptacle. Uterine seminal receptacle absent. Uterus extends posteriorly to vitellarium ; fills mostof hindbody and some of forebody. Eggs without anopercular spine. Vitelline masses entire;symmetrical; post-ovarian. Parasitic in stomach of marine teleosts. TYPE-SPECIES. Progonus muelleri (Levinsen, 1881) [by original designation]. COMMENT. In agreement with Poche (1926) and Bray (in press), Progonus Looss, 1899, cannot beconsidered a junior homonym ofProgona Berg, 1 882 (Recommendation of Article 36, InternationalRules of Zoological Nomenclature, 1926; Article 56(a), International Code of ZoologicalNomenclature, 1961). The apparent canalicular seminal receptacle present in this genus is essentially a type of blindseminal receptacle, especially as Laurer's canal does not open dorsally. The canalicular seminalreceptacle (sensu stricto) is not found in the Hemiuroidea, except in the case of Trifoliovarium, andis normally associated with the use of Laurer's canal as a vagina during copulation (see Gibson &Bray, 1975). Subfamily GONOCERCINAE Skrjabin & Guschanskaja, 1955Hemiperinae Yamaguti, 1958 Ventral sucker posterior to middle of body. Gut-caeca end blindly. Testes post-ovarian; tandemto symmetrical; near posterior extremity. Seminal vesicle usually small; oval to tubular; in fore-body. Pars prostatica tubular; short; linked to seminal vesicle by short, aglandular duct. Sinus-sac absent or poorly developed. Sinus-organ absent or present as small, blunt cone. Herma-phroditic duct absent or short. Genital atrium small or apparently absent. Ovary between testesand vitellarium. Laurer's canal present; opening dorsally; dilated proximally forming small rudi-mentary seminal receptacle. JueFs organ absent. Uterine seminal receptacle present. Uterus en-tirely pre-ovarian; most of coils usually in forebody. Eggs filamented or not. Vitellarium twoentire or indented, oval masses; symmetrical; antero- to postero-lateral to ovary. Parasitic instomach or branchial cavity of marine teleosts. Key to Gonocercinae 1. A. Eggs without filaments; sinus-sac and sinus-organ absent (but see comment on Gonocerca) GONOCERCAB. Eggs filamented; sinus-sac weakly developed; sinus-organ present. . . HEMIPERA THE HEMIUROIDEA 75 GONOCERCA Manter, 1925 [t(w,s>] Ventral sucker in posterior half of body. Testes tandem to almost symmetrical; at posteriorextremity of body. Seminal vesicle small; thin-walled; oval; close behind genital pore. Parsprostatica short; tubular. Sinus-sac and sinus-organ absent [see Comment]. Hermaphroditicduct absent (assuming that the small cavity into which male and female ducts open is the genitalatrium). Genital atrium small or apparently absent. Ovary median. Uterus entirely pre-ovarian;largely in forebody. Eggs without filaments. Vitelline masses lateral or antero-lateral to ovary;entire to indented. Parasitic in stomach of marine teleosts (especially in mid-ocean). TYPE-SPECIES. Gonocerca phycidis Manter, 1925 [by monotypy]. COMMENT. Manter (1934) described G. phycidis and G. crassa with a genital papilla present inboth, and Laurer's canal absent in the latter. Our sectioned material of G. phycidis indicates thata sinus-organ is absent and that a well-developed Laurer's canal is present (see Gibson, 1976:figs 14b and 14c). Since Manter's work there have also been conflicting opinions as to the presence of Laurer'scanal in G. crassa, Yamaguti (19386) stating it to be present and Rees (1953) absent. Both Rees(1953) and Brinkmann (1975) agree that a small but distinct genital atrium and genital papilla^sinus-organ) are present in G. crassa. If this is so, this species can hardly be considered to becongeneric with the other species of the genus. In view of the great morphological variability ofG. phycidis and the morphological similarity with Derogenes varicus, with which G. crassa hasbeen recorded, we consider that any change in its taxonomic status should await a completeredescription. HEMIPERA Nicoll, 1913 [t(w,s)] Hemiperina Manter, 1934 Ventral sucker in posterior half of body. Testes symmetrical to oblique at posterior extremity.Seminal vesicle oval to tubular. Pars prostatica tubular; short. Seminal vesicle and pars prostaticamay apparently be enclosed by common, sub-globular, parenchymatous capsule. Sinus-sacweakly developed ; with diffuse musculature ; enclosing base of sinus-organ and proximal regionof genital atrium. Sinus-organ a blunt cone. Male and female ducts may open separately on sinus-organ or form short hermaphroditic duct. Ovary median. Uterus entirely pre-ovarian; largely inforebody. Eggs filamented. Vitelline masses antero- to postero-lateral to ovary; entire or slightlyindented. Parasitic in stomach or branchial cavity of marine teleosts. TYPE-SPECIES. Hemipera ovocaudata Nicoll, 1913 [by original designation]. Subfamily HALIPEGINAE Poche, 1926 Arnolinae Yamaguti, 1958Monovitellinae Ataev, 1970 Ventral sucker usually near middle of body, occasionally more anterior or posterior. Gut-caecaend blindly or form cyclocoel. Testes pre-ovarian; symmetrical to oblique or occasionally tandemto oblique. Seminal vesicle globular to tubular; sometimes entirely or partly internal. Parsprostatica tubular to vesicular; normally short; sometimes internal. Sinus-sac present or absent;usually weakly developed ; may enclose pars prostatica and all or part of seminal vesicle. Sinus-organ present or absent; when present usually small, poorly developed and cone-shaped. Herma-phroditic duct usually short, occasionally long; rarely absent. Genital atrium small. Ovaryusually close to posterior extremity. Laurer's canal present; with dorsal pore or short and leadinginto Juel's organ. Rudimentary seminal receptacle often present when Laurer's canal opensdorsally. Blind or canalicular seminal receptacle absent. Uterine seminal receptacle present.Uterus entirely or almost entirely anterior to vitellarium; coils extend into forebody, except incases with ventral sucker inside anterior half of body. Eggs with or without filaments or threads. 76 D. I. GIBSON & R. A. BRAY Vitellarium one or two masses at posterior extremity of body; usually entire, but sometimes withindistinct or digitate lobes. Excretory bifurcation normally in hindbody, occasionally in forebody.Usually parasitic in gut (normally stomach) of freshwater teleosts; also recorded from brackishwater and marine teleosts close to the ancient Sarmatic Sea region (Caspian, Black and Mediter-ranean Seas), amphibians, reptiles and freshwater shrimps (the majority of genera occur in Asia). COMMENT. Certain genera of halipegines are closely related, differing basically in the apparentpresence or absence of filaments or threads on the eggs or in the degree of union between the twovitelline masses. One such group comprises Allotangiopsis, Chenia, Genarchopsis, Monovitellaand Tangiopsis, all of which occur in central, southern and south-east Asia. Another such groupis Arnold, Magnibursatus and possibly Anguillotrema and Tyrrhenia, which, with the exception ofAnguillotrema from central China, come from the Black or Mediterranean Seas. There appear to be fundamental differences in the seminal disposal apparatus in the femalereproductive system, as some genera possess Laurer's canal with a dorsal opening and othershave a fully developed Juel's organ. The systematic significance of this must await further work,because the arrangement in most of the genera is as yet unknown. Key to Halipeginae 1. A. Eggs with filaments or threads .......... 2 B. Eggs without filaments or threads 8 2. A. Cyclocoel present ........... B. Gut-caeca end blindly .4 3. A. Cyclocoel and excretory bifurcation in forebody .... ALLOTANGIOPSISB. Cyclocoel and excretory bifurcation in hindbody .... GENARCHOPSIS 4. A. Vitellarium a single mass CHENIA B. Vitellarium two similar masses .......... 5 5. A. Vitelline masses entire; sinus-sac completely enclosing pars prostatica and seminal vesicle; ventral sucker in anterior half of body; uterine coils retained in hindbody MA GNIBURSA TVSB. Vitelline masses usually lobed; ventral sucker near middle of body or more posterior; uterine coils extend into forebody ......... 6 6. A. Vitelline masses lobed (usually with 4 and 5 small lobes) or occasionally entire . . 7B. Vitelline masses with about 8 digitate extensions ..... THOMETREMA 7. A. Sinus-sac encloses pars prostatica and entire seminal vesicle; vitelline masses lobed ANGUILLOTREMA B. Sinus-sac usually weakly developed or (?) absent, sometimes enclosing prostatica gland-cells, occasionally enclosing pars prostatica, rarely enclosing distal extremity of seminalvesicle; vitelline masses usually lobed, occasionally entire . . . HALIPEGUS 8. A. Cyclocoel present; ventral sucker near middle of body; uterine coils extend into forebody 10B. Gut-caeca end blindly 9 9. A. Ventral sucker in anterior half of body; uterine coils retained in hindbody . . . 11B. Ventral sucker near middle of body; uterine coils extend into forebody. . TYRRHENIA 10. A. Vitellarium a single mass MONOVITELLA B. Vitellarium two similar masses situated close together .... TANGIOPSIS 11. A. Sinus-sac encloses pars prostatica and seminal vesicle ARNOLA B. Sinus-sac small, not enclosing pars prostatica and seminal vesicle. . . DEROPEGUS HALIPEGUS Looss, 1899 [t(w); n(w,s)] Genarchella Travassos, Artigas & Pereira, 1928Vitellotrema Guberlet, 1928Dollfuschella Vercammen-Grandjean, 1960Progenarchopsis Fischthal, 1976Paravitellotrema Watson, 1976 Ventral sucker near middle of body. Gut-caeca end blindly. Testes symmetrical to slightlyoblique. Seminal vesicle saccular. Pars prostatica short; often reduced. Sinus-sac usually weakly THE HEMIUROIDEA 77 developed or ( ?) absent ; often enclosing pars prostatica and, on some occasions, distal extremityof seminal vesicle. Temporary sinus-organ may be developed as conical papilla (may occasionallybe permanent); on some occasions male and female ducts open separately through this papilla.Hermaphroditic duct, when present, short. Genital atrium normally small. Ovary usually separa-ted from testes by uterus, but not always. Laurer's canal present, with dorsal pore; proximalregion dilate forming rudimentary seminal receptacle. Juel's organ absent. Uterus not extendingposteriorly to vitellarium; usually with about equal distribution in fore- and hindbodies. Eggswith long, single filament at anopercular pole. Vitellarium two relatively symmetrical masses;usually clearly four- and five-lobed, sometimes indistinctly lobed or entire. Parasitic in upperregions of gut (usually stomach) of freshwater teleosts, amphibians and reptiles; those fromamphibians often recorded from mouth, one record from ear (Cosmopolitan). TYPE-SPECIES. Halipegus ovocaudatus (Vulpian, 1859) [by monotypy]. COMMENT. Our concept of Halipegus may be considered wide; but, until more of the constituentspecies have been carefully and critically described, we believe that this concept is the most useful.In particular there appears to be a need for careful descriptions of the terminal genitalia in thisgenus: that of the type-species, for instance, is poorly known. The vitellarium is rather variable,the paired masses being distinctly lobed in the type-species and in most other species in the genus,weakly or indistinctly lobed in some species [e.g. H. kessleri (Grebnitzky, 1872)] and entire insome species [e.g. H. [Vitellotrema] fusipora (Guberlet, 1928), H. [=Genarchella] parva(Travassos, Artigas & Pereira, 1928) and the two species of Paravitellotrema Watson, 1976].Halipegus cryptorchis Mane-Garzon & Gascon, 1973, is morphologically similar to Deropegus,especially in the rather anterior position of the ventral sucker. It differs, however, in the eggsbeing filamented and that part of the uterus is coiled in the forebody. ALLO TANGIOPSIS Yamaguti, 1971 Ventral sucker in middle of body. Cyclocoel present in forebody. Testes symmetrical to oblique.Seminal vesicle tubular, stout, recurved. Pars prostatica short, tubular; not delimited. Sinus-sacforms muscular wall surrounding hermaphroditic duct (?). Sinus-organ absent (?). Laurer's canaland Juel's organ (?). Seminal receptacle reported [presumably either rudimentary type or Juel'sorgan]. Uterine seminal receptacle situated, at least partly, in distal region of uterus. Uterus notreaching posterior to vitellarium; significant proportion present in forebody. Eggs filamented.Vitellarium two lobed masses; slightly oblique; at posterior extremity. Excretory bifurcation inforebody. Parasitic in gonads of freshwater shrimps as (?) progenetic metacercaria (China). TYPE-SPECIES. Allotangiopsis shanghaiensis (Yeh & Wu, 1955) [by original designation]. COMMENT. This genus is similar to Tangiopsis, differing only in the presence of filamented eggsand in the anterior positions of the cyclocoel and the excretory bifurcation. The latter differencesmight be explained by the relatively caudal position of the ventral sucker, a characteristic ofmetacercariae. ANGUILLOTREMA Chin & Ku, 1974 Ventral sucker in posterior half of body. Gut-caeca end blindly. Testes symmetrical. Seminalvesicle tubular; coiled; internal. Pars prostatica vesicular; internal. Sinus-sac large; weaklymuscled; enclosing pars prostatica and seminal vesicle. Sinus-organ muscular; conical. Laurer'scanal and Juel's organ (?). Uterus entirely anterior to vitellarium; large proportion in forebody.Eggs with a filament at each end and small threads surrounding base of filament at one end.Vitellarium two masses with four and five lobes; symmetrical at posterior extremity. Parasitic instomach of eels in freshwater (China). TYPE-SPECIES. Anguillotrema papillatum Chin & Ku, 1974 [by original designation]. 78 D. I. GIBSON & R. A. BRAY ARNOLA Strand, 1942 [t(w,s)] Arnoldia Vlasenko, 1931, nee Mayer-Eymar, 1887 Ventral sucker in anterior half of body. Gut-caeca end blindly close to posterior extremity. Testesoblique; separated by uterus. Seminal vesicle coiled, tubular; internal. Pars prostatica short,straight; internal. Sinus-sac enclosing seminal vesicle and pars prostatica plus metraterm distally.Permanent sinus-organ absent. Short hermaphroditic duct and genital atrium present. Ovaryimmediately posterior to hind testis. Short, dilate Laurer's canal, containing sperm, opens intowell-developed Juel's organ. Uterine seminal receptacle present. Uterus entirely anterior tovitellarium; coils not extending into forebody. Eggs without filaments. Vitellarium two sym-metrical masses; situated close together at posterior extremity; slightly indented, usually indicatingthree and four lobes. Parasitic in stomach of marine teleosts (Diplodus) in Black Sea and AdriaticSea. TYPE-SPECIES. Arnold microcirrus (Vlasenko, 1931) [by original designation]. COMMENT. The low salinity of the Black Sea and the similarity between this genus and severalgenera from freshwater in Central Asia and the Far East suggest that Arnola might be a relictfrom the ancient Sarmatic Sea, which arose in the upper Miocene epoch, contained brackish waterand extended from the Black Sea region easterly into Central Asia. Our finding Arnola in theAdriatic Sea in no way invalidates this hypothesis, as a connection between this region of theMediterranean Sea and the Sarmatic Sea (then called the Karangat Sea) occurred briefly duringthe Pleistocene epoch [see Zenkevitch, 1947; Ekman, 1953; Miller, 1972].This genus appears to be closely related to Magnibursatus, Anguillotrema and Tyrrhenia. CHENIA Hsu, 1954 Ventral sucker just posterior to middle of body. Gut-caeca terminate blindly at level of ovary.Testes oblique. Seminal vesicle a curved, elongate sac. Pars prostatica internal (?; see figure 1 ofHsu). Sinus-sac enclosing attenuated anterior portion of seminal vesicle and pars prostatica.Sinus-organ not reported. (?) Seminal receptacle (presumably either rudimentary or Juel's organ)reported. Uterus entirely pre-ovarian; coils extending into forebody. Eggs reniform; with twofilaments at one pole. Vitellarium single compact mass at posterior extremity. Parasitic in gut offreshwater gobiid teleosts (China). TYPE-SPECIES. Chenia cheni Hsu, 1954 [by monotypy]. DEROPEGUS McCauley & Pratt, 1961Parahalipegus Wootton & Powell, 1964 Ventral sucker in anterior half of body. Gut-caeca end blindly near posterior extremity. Testestandem, oblique or symmetrical. Seminal vesicle saccular. Pars prostatica short; tubular toslightly vesicular; surrounded by dense layer of gland-cells. Sinus-sac apparently present, butweakly developed; small. Sinus-organ a muscular cone. Ovary usually separated from testes byloops of uterus. Laurer's canal present; apparently opening dorsally; slightly dilated proximally,forming a rudimentary seminal receptacle. Juel's organ presumably absent. Uterine coils not ex-tending into forebody; one loop may reach posterior to vitellarium. Eggs without filaments.Vitellarium two symmetrical to oblique, entire or slightly lobed masses; close to posteriorextremity. Parasitic in stomach of amphibians and teleosts in freshwater (North America). TYPE-SPECIES. Deropegus aspina (Ingles, 1936) [by original designation]. GENARCHOPSIS Ozaki, 1925 Ophiocorchis Srivastava, 1933 ( ?) Pseudogenarchopsis Yamaguti, 1971 THE HEMIUROIDEA 79 Ventral sucker in posterior half, or occasionally in middle, of body. Cyclocoel present in hind-body; oesophageal pouch often present. Testes usually oblique, occasionally symmetrical.Seminal vesicle tubular to elongate-saccular; coiled. Pars prostatica short; may be slightly vesi-cular. Sinus-sac not clearly described, but may be weakly developed and enclose pars prostaticaand perhaps distal extremity of seminal vesicle. Sinus-organ a strongly muscular, blunt cone.Ovary usually sinistral and well posterior to testes. Laurer's canal opening into well-developedJuel's organ, or apparently opening dorsally (?). Uterus entirely pre-ovarian; coils extending intoforebody. Eggs with long, polar filament. Vitellarium two entire or indented masses at posteriorextremity; symmetrical to oblique. Parasitic mainly in stomach of freshwater teleosts, but thereare two records from amphibians and two probable accidental infestations of snakes (SouthernAsia and Far East). TYPE-SPECIES. Genarchopsis goppo Ozaki, 1925 [by original designation]. COMMENT. Genarchopsis thapari Gupta & Chakrabarti, 1967, from the intestine of a snake, isknown only from four immature worms, and it is probably a fish-parasite which has been in-gested by the wrong host. Yamaguti (1971) erected the genus Pseudogenarchopsis for this species;but his only apparent valid criterion for doing so is that this species is purported to have a cirrus-sac. As far as Ophiocorchis is concerned, this genus is said to differ from Genarchopsis in posses-sing an oesophageal pouch. Rai (1972) found this feature either present or absent in one species(G. goppo), and it cannot be considered a character of generic importance. A well-developed Juel's organ in G. punctati Agrawal, 1966, was described by Anjaneyulu(1967) and Madhavi & Rao (1974); but Ozaki (1925) described G. goppo, the type-species, ashaving Laurer's canal which opened dorsally. It seems unlikely that species with such apparentlydifferent seminal and vitelline disposal apparatus could be congeneric, but more detailed infor-mation is required on G. goppo and other species in this genus in order to resolve this problem.Both Rai (1972) and Pandey (1975) also note the presence of Laurer's canal in G. goppo, butneither of them states how it terminates. MAGNIBURSATUS Naidenova, 1969 Ventral sucker in anterior half of body. Gut-caeca end blindly close to posterior extremity. Testesoblique, in anterior hindbody. Seminal vesicle coiled, tubular; internal. Pars prostatica short,straight; internal. Sinus-sac enclosing seminal vesicle and pars prostatica, plus the metratermdistally; in forebody. Sinus-organ absent. Short hermaphroditic duct or genital atrium present.Laurer's canal ends blindly (? in Juel's organ). Uterine seminal receptacle present. Ovary nearposterior extremity; separated from testes by uterus. Uterus entirely anterior to vitellarium;coils not extending into forebody. Eggs with several (? six to eight) filaments (? threads) at eachend. Vitellarium two oblique to symmetrical masses; close together at posterior extremity.Parasitic in stomach of euryhaline or marine teleosts (Black Sea region). TYPE-SPECIES. Magnibursatus skrjabini (Vlasenko, 1931) [by original designation]. MONOVITELLA Ataev, 1970 Ventral sucker in middle of body. Cyclocoel present in hindbody. Testes symmetrical. Seminalvesicle saccular. Pars prostatica short; vesicular. Sinus-sac reported absent (figure suggests itmight be present as weakly muscled, tubular jacket of hermaphroditic duct). Sinus-organabsent (?). Genital atrium short. Ovary lateral; apparently extra-caecal ; situated between righttestis and vitellarium. Laurer's canal and Juel's organ (?). Uterus almost entirely anterior tovitellarium, but descending loop reaches close to posterior extremity; coils extend into forebody.Eggs not filamented. Vitellarium a single, entire mass; lateral; apparently extra-caecal betweenovary and posterior extremity. Parasitic in intestine of brackish water teleosts (Caspian Sea). TYPE-SPECIES. Monovitella cyclointestina Ataev, 1970 [by original designation]. COMMENT. Monovitella, despite certain apparent differences, is remarkably similar to Tangiopsis, 80 D. I. GIBSON & R. A. BRAY both of which are reported from gobiid fishes. Future work might show the two to be synonymous.Chenia is also morphologically similar and reported from gobiid fishes. TANGIOPSIS Skrjabin & Guschanskaja, 1955 Ventral sucker in middle of body. Cyclocoel present; caeca unite anterior to testes. Testes sym-metrical to oblique. Seminal vesicle tubular; recurved. Pars prostatica small; free in parenchyma(according to Tang, 1951; but his figure suggests that the prostatic glands may be delimited orthat the duct is vesicular and he has omitted the external gland-cells). Sinus-sac apparently absent.Temporary sinus-organ may be present (?). Ovary between right testis and vitellarium. Laurer'scanal opens dorsally. Juel's organ presumably absent. Rudimentary seminal receptacle apparentlypresent. Uterus not passing posterior to vitellarium; almost entirely pre-ovarian; coils extend intoforebody ; apparently filled with spermatozoa throughout most of its length. Eggs without fila-ments. Vitellarium two slightly indented, symmetrical masses ; close together at posterior extremity ;united by short duct. Parasitic in stomach of freshwater teleosts (China). TYPE-SPECIES. Tangiopsis chinensis (Tang, 1951) [by original designation].COMMENT: This genus is similar to Monovitella. THOMETREMA Amato, 1968 Ventral sucker in middle of body. Gut-caeca end blindly near posterior extremity. Testes obliqueto symmetrical; separated by loops of uterus. Seminal vesicle tubular; stout; attenuated anterior-ly; recurved. Pars prostatica with narrow lumen; surrounded by dense, oval mass of gland-cells.Sinus-sac not reported, but possibly present surrounding long hermaphroditic duct (see figures ofSzidat, 1954). Sinus-organ present as small papilla in base of oval genital atrium (not reported byAmato, 1968). Ovary near posterior extremity; separated from testes by many loops of uterus;may have slightly irregular outline. Laurer's canal and Juel's organ (?). Uterus entirely pre-ovarian ; coils extending into forebody. Eggs with one polar filament. Vitellarium two symmetricalmasses of about eight short, digitate lobes, which are irregularly expanded distally. Parasitic instomach of freshwater teleosts (Plecostomus}, occasionally in estuarine conditions (SouthAmerica). TYPE-SPECIES. Thometrema magnified (Szidat, 1954) n. comb. [syn. T. portoalegrensis Amato,1968 - type by original designation]. COMMENT. This genus was erected for a new species, T. portoalegrensis, from Plecostomus com-mersoni in Brazil by Amato (1968). The species Gonocercella magnified was described by Szidat(1954) from the same host in the estuary of the River Plate and from Plecostomus plecostomus ina neighbouring locality to Amato's record. Szidat's description is identical to that of Amato,with the exception that he described and figured the terminal genitalia in more detail and didnot observe the filament on the egg. Considering that there is no evidence that Szidat teased outthe eggs or sectioned his specimens, we have little hesitation in synonymizing the two species, asthe presence of filamented eggs is often difficult to ascertain in whole-mounts. TYRRHENIA* Paggi & Orecchia, 1975 Ventral sucker near middle of body. Gut-caeca end blindly near posterior extremity. Testesoblique. Seminal vesicle saccular, but attenuated distally; internal. Pars prostatica (?) short,tubular (according to Paggi & Orecchia the prostatica cells empty into the hermaphroditic duct);internal. Sinus-sac enclosing entire seminal vesicle and pars prostatica, plus metraterm distally.Permanent sinus-organ absent. Hermaphroditic duct short. Genital atrium apparently absent (orsmall). Laurer's canal present, with rudimentary seminal receptacle. Juel's organ absent. Uterine * Paggi & Orecchia (1974) first used this name in an abstract, but without an accompanying description. THE HEMIUROIDEA 81 seminal receptacle present. Ovary immediately posterior to hind testis. Uterine coils reach pos-teriorly to vitellarium and extend into forebody. Eggs without filaments. Vitellarium two entire,symmetrical masses; situated close together immediately posterior to ovary and close to posteriorextremity. Parasitic in stomach and on gills of marine teleosts (Blennius) in Mediterranean(Tyrrhenian) Sea. TYPE-SPECIES. Tyrrhenia blennii Paggi & Orecchia, 1975 [by original designation]. CHELATREMA Gupta & Kumari, 1970, gen. inq.Genus of uncertain position This genus was erected in an abstract by Gupta & Kumari (1970) for a new species, C. smythi[type by monotypy], from the Indian freshwater fish Chela baccala. It is said to belong to thesubfamily Arnolinae of the family Hemiuridae. The genus is unrecognizable from the briefdefinition given, and appears to have characters unusual, or unknown, in the Hemiuroidea. Family DICTYSARCIDAE Skrjabin & Guschanskaja, 1955 Cylindrorchiidae Poche, 1926 Aerobiotrematidae Yamaguti, 1958 Pelorohelminthidae Fischthal & Kuntz, 1964 Albulatrematidae Yamaguti, 1965 Tetrasteridae Oshmarin, 1965 Dollfustravassosiidae Teixeira de Freitas & Kohn, 1967 Body usually large; oval; stout or flattened. Ecsoma absent. Body-surface smooth. Oral andventral suckers well developed; ventral sucker in anterior half of body. Pharynx well developed.Oesophagus short. 'Driisenmagen' normally present (?). Gut-caeca end blindly close to posteriorextremity. Testes two; large; symmetrical; oval or elongate; pre-ovarian; just posterior to ventralsucker. Seminal vesicle tubular; in forebody. Pars prostatica tubular. Sinus-sac well developed,poorly developed or absent. Permanent sinus-organ absent (? or present as small papilla); tem-porary sinus-organ may form. Genital atrium small or absent. Hermaphroditic duct well develop-ed or indistinguishable from genital atrium ; sometimes appears to be continuation of metratermwith ejaculatory duct entering laterally. Ovary oval or with four (or five) short or elongate lobes;normally separated from testes by loops of uterus. JuePs organ* and uterine seminal receptaclepresent. Laurer's canal and blind or canalicular seminal receptacle absent. Uterus almost entirelyretained in hindbody; mainly pre-ovarian or with many loops in post-ovarian field. Eggs withoutfilaments; may link together and form chains. Vitellarium with six to eight (usually seven,arranged three and four) oval to digitiform lobes, or with two lateral acinous groups of folliclesor two compact multilobulate masses ; postero- to antero-lateral or posterior to ovary. Excretoryarms united in forebody. Parasitic in swim-bladder of physostomatous teleosts in a marineenvironment. COMMENT: The almost unique niche of these parasites in the swim-bladder of physostomatousteleosts is shared in the Hemiuroidea by the genus Isoparorchis. Although considered to be closelyrelated to the members of the Dictysarcidae by many authors, the latter genus differs because itoccurs in a freshwater teleost and possesses several primitive features, such as Laurer's canal, atubular vitellarium and a well-developed, muscular sinus-organ. Key to Dictysarcidae 1. A. Uterus mainly pre-ovarian ........... 2 B. Uterine field mainly post-ovarian . . CYLINDRORCHIINAE subfam. inq. (p. 83) * Observed in Elongoparorchis (see Madhavi & Rao, 1974) and Dictysarca (see Manter, 1947). 82 D. I. GIBSON & R. A. BRAY 2. A. Ovary oval (entire or irregularly lobed); vitellarium two compact multilobulate masses ortwo acinous bunches of follicles; hermaphroditic duct indistinguishable from genital atrium DICTYSARCINAE (p. 82) B. Ovary 4- (or 5-) lobed ; vitellarium 6-8 (usually 7) digitiform to oval lobes ; hermaphroditic duct distinguishable from genital atrium. . . . ALBULATREMATINAE (p. 82) Subfamily DICTYSARCINAE Skrjabin & Guschanskaja, 1955 Body stout. Cuticular ridge may encircle mid-hindbody. Testes oval; entire or irregularly lobed.Sinus-sac and sinus-organ absent. Hermaphroditic duct indistinguishable from genital atrium;tubular; short. Ovary oval; entire or irregularly lobed; in posterior third of hindbody. Uterusmainly pre-ovarian, but some loops present in post-ovarian field. Vitellarium two compactmultilobulate masses or two acinous bunches of follicles; antero- or postero-lateral to ovary.Usually parasitic in marine eels. Key to Dictysarcinae 1 . A. Cuticular ridge encircling mid-hindbody absent ; ovary irregularly lobed ; vitellarium in two, compact, multilobulate masses ........ DICTYSARCA B. Cuticular ridge encircling mid-hindbody present ; ovary unlobed ; vitellarium two groups of acinous follicles AEROBIOTREMA DICTYSARCA Linton, 1910 No cuticular ridge present encircling mid-hindbody. Testes irregularly lobed. Seminal vesiclesinuous. Pars prostatica well developed. Hermaphroditic duct appears to be continuation ofmetraterm, with ejaculatory duct entering laterally. Ovary large; irregularly lobed. Vitellariumtwo compact, multilobulate masses; antero-lateral to ovary. Parasitic in moray eels (Gymnothorax)and sea-horses (Hippocampus). TYPE-SPECIES. Dictysarca virens Linton, 1910 [by original designation]. AEROBIOTREMA Yamaguti, 1958 Cuticular ridge present encircling mid-hindbody. Testes entire. Seminal vesicle sigmoid. Parsprostatica straight. Ovary small; entire. Vitellarium two acinous bunches of follicles; one antero-and one postero-lateral to ovary. Excretory arms with numerous anastomosing side branches,mostly lying close to caeca. Parasitic in marine eels (Muraenesox). TYPE-SPECIES. Aerobiotrema muraenesocis Yamaguti, 1958 [by original designation]. Subfamily ALBULATREMATINAE Yamaguti, 1965 Pelorohelminthinae Fischthal & Kuntz, 1964Tetrasterinae Oshmarin, 1965 Body flattened to stout. Testes large; oval or elongate. Sinus-sac present; well or poorly developed.Hermaphroditic duct distinguishable from genital atrium. Ovary four (or five) distinct, oval orelongate lobes; in middle or posterior half of hindbody. Uterus mainly pre-ovarian or extendingthroughout hindbody. Vitellarium seven (occasionally six or eight) digitiform to oval lobes;immediately posterior or postero-lateral to ovary. Parasitic in marine ( ? or brackish water)teleosts. Key to Albulatrematinae LA. Vitelline lobes, ovarian lobes and testes oval ; ovary in middle of hindbody ; significant pro-portion of uterus post-ovarian. ....... ALBULATREMA THE HEMIUROIDEA 83 B. Vitelline lobes and ovarian lobes digitiform; testes elongate; ovary well inside posterior half of hindbody; most of uterus pre-ovarian . . . . ELONGOPARORCHIS ALBULATREMA Yamaguti, 1965 Body stout. Testes oval. Seminal vesicle tubular; narrow; convoluted [according to Yamaguti,1965, the seminal vesicle is replaced by a vas deferens, the distal portion of which is stronglymuscular, convoluted and enclosed by an apparently muscular capsule]. Pars prostatica sigmoid;delimited. Sinus-sac well developed; bulbous. Temporary sinus-organ may be present. Genitalatrium absent or (?) small. Ovary in middle of hindbody; ovarian lobes oval. Uterus extendsthroughout hindbody, much of it post-ovarian. Vitelline lobes oval to pyriform. Parasitic inmarine (? or brackish water) teleosts (Albuld). TYPE-SPECIES. Albulatrema ovale Yamaguti, 1965 [by original designation]. ELONGOPARORCHIS Rao, 1961 [n(w)] Pelorohelmins Fischthal & Kuntz, 1964 Tet raster Oshmarin, 1965 Dollfustravassosius Teixeira de Freitas & Kohn, 1967 Body flattened to stout. Testes elongate. Seminal vesicle sinuous; may reach dorsally to ventralsucker. Pars prostatica short. Sinus-sac poorly developed; present only distally as vestige sur-rounding base of genital atrium. Sinus-organ a small papilla-like structure (? temporary).Hermaphroditic duct relatively long; formed as continuation of metraterm, with ejaculatoryduct entering laterally. Genital atrium oval or elongate-oval. Ovary well inside posterior half ofhindbody; ovarian lobes digitiform. Uterus mainly pre-ovarian. Eggs may be linked togetherforming chains. Vitelline lobes digitiform; with condensed follicular appearance. Parasiticespecially in catfishes, such as Arius. TYPE-SPECIES. Elongopar orchis pneumatis Rao, 1961 [by original designation]. COMMENT. In some descriptions of species of this genus Mehlis' gland has been considered to bethe ovary and the ovary to be anterior lobes of the vitellarium (see Fischthal & Kuntz, 1964a;Teixeira de Freitas & Kohn, 1967; Fischthal & Thomas, 1968; but cf. Yamaguti, 1971). Subfamily CYLINDRORCHIINAE Poche, 1926, status emend, (subfam. inq.) [Original description inadequate.] Body elongate-oval. Testes elongate. Terminal genitalia notknown. Ovary small; oval; just inside posterior half of hindbody. Uterus convoluted posteriorto ovary ; straight anterior to ovary. Vitellarium two clusters of small follicles ; antero-lateral toovary. Parasitic in marine (? or brackish water) teleosts (Tetrodori). CYLINDRORCHIS Southwell, 1913, gen. inq.Defined as subfamily.TYPE-SPECIES. Cylindrorchis tenuicutis Southwell, 1913 [by original designation]. COMMENT. We have included Cylindrorchis as a genus inquirendus because the original descriptionof C. tenuicutis is inadequate. Southwell (1913) states: 'As only very few specimens of this parasitewere obtained, it was found impossible to satisfactorily make out with certainty, the precisedetails of the reproductive system. I am therefore not certain that the following description isabsolutely correct in every detail'. If Southwell had confused the uterus with the vitellarium, thevitellarium for the ovary and the ovary for Mehlis' gland or JueFs organ, then it is conceivablethat he may have been dealing with immature specimens of Ehngoparorchis. Theoretically, the oldest family-group name available in this family is Cylindrorchiidae Poche,1926; but, due to the questionable validity of Cylindrorchis, we feel that it would be inadvisable,at this stage, to use this genus as the type-genus of the family. 84 D. I. GIBSON & R. A. BRAY Family HEMIURIDAE Looss, 1899 Lecithochiriidae Liihe, 1901 Dinuridae Looss, 1907 Elytrophallidae Skrjabin & Guschanskaja, 1954 Body usually small, but elongate. Ecsoma present, occasionally reduced or vestigial. Body-surface smooth or with annular plications; the latter occasionally being serrate giving a scaleyappearance. Presomatic pit or ventro-cervical groove occasionally present. Oral and ventralsuckers well developed; usually close together. Pharynx well developed. Oesophagus usuallyshort. 'Driisenmagen' normally present. Gut-caeca terminate blindly; usually within ecsoma.Testes two; tandem, oblique or symmetrical; pre-ovarian; in hindbody. Seminal vesicle tubular,saccular or constricted into portions; muscular or thin-walled; in fore- or hindbody. Pars prosta-tica of variable length; usually tubular, but occasionally vesicular; may be linked to seminalvesicle by aglandular duct. Ejaculatory duct, if present, usually short. Sinus-sac usually welldeveloped, occasionally reduced or absent. Prostatic or ejaculatory vesicle occasionally presentwithin sinus-sac. Hermaphroditic duct usually enclosed within sinus-sac. Permanent sinus-organ and genital atrium well developed, small or absent; temporary sinus-organ may form fromhermaphroditic duct in some cases. Genital pore mid-ventral at level of oral sucker or pharynx.Ovary oval; usually entire; post-testicular. Mehlis' gland post-ovarian. Laurer's canal andcanalicular or blind seminal receptacle absent. Juel's organ and uterine seminal receptacle present.Uterus coiled mainly in pre- and/or post-ovarian region of hindbody; few or no coils present inforebody; initially descending into or towards ecsoma and then ascending towards forebody.Eggs numerous; small; embryonated; rarely with a polar filament. Vitellarium varies betweenforms with seven tubular branches (three on one side of body, four on other) and forms withtwo distinct, oval masses; mainly post-ovarian. Excretory vesicle Y-shaped; arms united in fore-body or not. Parasitic mainly in gut, especially stomach, of marine teleosts, occasionally presentin gut of freshwater teleosts and lung of sea-snakes. Key to Hemiuridae 1. A. Ejaculatory (or prostatic) vesicle present within sinus-sac, occasionally partly external [this vesicle should not be confused with a pars prostatic which is also present] . . 2B. Ejaculatory (or prostatic) vesicle absent ......... 4 2. A. Long, convoluted hermaphroditic duct and thin-walled permanent sinus-organ present; seminal vesicle bipartite, anterior part muscular; vitellarium 2 irregularly oval masses GLOMERICIRRINAE (p. 90) B. Hermaphroditic duct relatively straight; permanent sinus-organ absent; seminal vesicletubular or saccular and partitioned, usually thin-walled; vitellarium 7 digitiform to ovallobes or with tendency to form 2 distinct, often lobed, lateral masses; ecsoma sometimesreduced or apparently absent .......... 3 3. A. Eggs with polar filament ; commonly parasitic under surface of liver HYPOHEPATICOLINAE (p. 91)B. Eggs without polar filaments; normally parasitic in gut . LECITHOCHIRIINAE (p. 91) 4. A. Sinus-sac absent or poorly developed, when present usually of 'open'-type; seminal vesicle entirely or mainly thin-walled, usually constricted into portions; ecsoma sometimes poorly developed PLERURINAE (p. 95) B. Sinus-sac present, usually well developed, occasionally small ..... 5 5. A. Vitellarium 2 symmetrical to slightly oblique, entire or lobed masses .... 6B. Vitellarium 7 distinct oval to tubular lobes ........ 8 6. A. Seminal vesicle oval or bipartite, in fore- or hindbody; ecsoma well developed; parasitic in gut of marine teleosts ........... 7 B. Seminal vesicle tubular, extending well into hindbody; ecsoma reduced; parasitic in lung of sea-snakes PULMOVERMINAE (p. 98) 7. A. Body-surface smooth; seminal vesicle in forebody, oval, thick-walled; sinus-sac very small LETHADENINAE (p. 95)B. Body-surface with plications or 'scales'; seminal vesicle in hindbody, oval or bipartite, thin- or partly to entirely thick-walled HEMIURINAE (p. 85) THE HEMIUROIDEA 85 8. A. Seminal vesicle with thick muscular wall, oval; permanent sinus-organ normally delicate and amuscular ELYTROPHALLINAE (p. 89) B. Seminal vesicle thin-walled and oval, tubular or constricted into portions; permanentsinus-organ large and muscular, reduced to small papilla or apparently absent DINURINAE (p. 86) Subfamily HEMIURINAE Looss, 1899 Ecsoma well developed. Body-surface plicated or 'scaley' (i.e. with crenulate plications). Preso-matic pit absent. Testes tandem to oblique. Seminal vesicle thin-walled, or partially or slightlymuscular; bipartite or oval; in hindbody. Pars prostatica tubular; long; gland-cells occasionallydelimited by membrane. Sinus-sac present ; often tubular ; not enclosing prostatic vesicle. Perma-nent sinus-organ absent, but hermaphroditic duct may be protruded to form temporary sinus-organ. Genital atrium usually small, but variable in length. Ovary oval. Vitellarium composed oftwo distinct oval masses, but these may show slight tendency toward lobation in three and fourstyle. Excretory arms united in forebody. Parasitic in stomach of marine teleosts. Key to Hemiurinae 1. A. Seminal vesicle bipartite HEMIURUS B. Seminal vesicle oval ............ 2 2. A. Plications on body-surface normal PARAHEMIURUS B. Plications on body-surface crenulate, giving 'scaley' appearance . . ANAHEMIURUS HEMIURUS Rudolphi, 1809 [t(w,s); n(w, s)] Apoblema Dujardin, 1845Pronopyge Looss, 1899 (see p. 73).Metahemiurus Skrjabin & Guschanskaja, 1954 Body-surface with normal plications. Seminal vesicle constricted into two portions (? occasionallythree), one of which may have thick, muscular wall. TYPE-SPECIES. Hemiurus appendiculatus (Rudolphi, 1802) [by subsequent designation: Stiles &Hassall, 1898]. COMMENT. Two subgeneric names have been erected: Metahemiurus Skrjabin & Guschanskaja,1954, based upon sucker-ratios, the extent of the surface plications and the length of the ecsoma;and Neohemiurus Slusarski, 1958, based upon the presence of plications on the ecsoma. Theformer features are either variable or only of specific value, and the latter feature, plications onthe ecsoma, is extremely doubtful (see p. 48) and requires confirmation. Metahemiurus has beenused at the generic level by Brinkmann (1975). ANAHEMIURUS Manter, 1947 Body-surface with 'scaley' appearance (i.e. with crenulate plications). Seminal vesicle oval; withrelatively thick, muscular wall. TYPE-SPECIES. Anahemiurus microcercus Manter, 1947 [by original designation]. PARAHEMIURUS Vaz & Pereira, 1930 [t(w)] Body-surface with normal plications. Seminal vesicle oval; with muscular wall of variablethickness. TYPE-SPECIES. Parahemiurus merus (Linton, 1910) [syn. P. parahemiwus Vaz & Pereira, 1930-type by original designation]. 86 D. I. GIBSON & R. A. BRAY Subfamily DINURINAE Looss, 1907Stomachicolinae Yamaguti, 1958 Ecsoma well developed ; occasionally large. Body surface plicated or smooth (apparently occasion-ally striated). Presomatic pit absent. Testes symmetrical to tandem; usually oblique. Seminalvesicle thin- walled; oval to tubular; may be constricted into two to four portions; in forebody,dorsal to ventral sucker or in hindbody. Pars prostatica tubular or vesicular; short or long; maybe linked to seminal vesicle by aglandular duct. Sinus-sac present; small or large; usually oval;not enclosing a prostatic vesicle. Permanent sinus-organ large and muscular, reduced to smallpapilla or apparently absent. Genital atrium usually well developed; deep or shallow (oftendepending upon contraction). Ovary usually oval; occasionally reniform or lobed. Terminalportion of uterus may or may not form distinct vesicle just outside sinus-sac. Vitellarium normallyseven tubular lobes ; three on one side, four on the other. Excretory arms united or not united inforebody. Normally parasitic in stomach of marine teleosts. Key to Dinurinae 1. A. Seminal vesicle usually (but not always) constricted into portions; permanent sinus-organ present, but occasionally reduced to small papilla (sectioning usually required); parsprostatica usually linked to seminal vesicle by distinct aglandular duct ... 2B. Seminal vesicle not constricted into portions; permanent sinus-organ usually apparentlyabsent, but may be present as small papilla; pars prostatica not normally linked toseminal vesicle by distinct aglandular duct ........ 2. A. Body-surface with plications ........... 3 B. Body-surface without plications .......... 4 3. A. Pars prostatica long, may be sparsely surrounded by gland-cells; seminal vesicle trilocular DINURUS B. Pars prostatica short, connected to seminal vesicle by long aglandular duct; seminal vesicle variable, tubular, saccular or divided into 2 or 3 sections . . ECTENURUS 4. A. Glandular region of pars prostatica short; excretory arms unite in forebody; distal end of uterus often vesicular ........... 5 B. Glandular region of pars prostatica long; distal end of uterus not vesicular ... 6 5. A. Aglandular region of pars prostatica long; seminal vesicle dorsal or postero-dorsal to ventral sucker; sinus-sac usually dilate proximally ERILEPTURUS B. Aglandular region of pars prostatica short; seminal vesicle in forebody; sinus-sac elongate oval . ATHERIA 6. A. Parasitic in stomach of marine teleosts; pars prostatica connected to seminal vesicle by short aglandular duct; excretory arms not united in forebody . . . PARADINURUSB. Parasitic in intestine of freshwater teleosts .... (?) PROSTERRHURUS 1. A. Anterior part of hindbody greatly attenuated; pars prostatica in two parts separated by long aglandular duct . MECODERUS B. Anterior part of hindbody with normal configuration; pars prostatica undivided . . 8 8. A. Ecsoma large; seminal vesicle oval or elongate-oval 9 B. Ecsoma normal ; seminal vesicle tubular and sinuous .... TUBULOVESICULA 9. A. Seminal vesicle in forebody ALLOSTOMACHICOLA B. Seminal vesicle in hindbody . . . STOMACHICOLA COMMENT. We considered separating this group into two, using the features in the first part of thekey, because of the functional association between the presence of a permanent sinus-organ and aseminal vesicle constricted into sections by sphincter muscles (see p. 129). The two groups,however, appear to grade into one another. DINURUS Looss, 1901 [n(w,s)] Body-surface with plications. Seminal vesicle trilocular, or occasionally quadrilocular; in anteriorhindbody or occasionally postero-dorsal to ventral sucker. Pars prostatica long; may be denselyor sparsely invested by gland-cells; linked to seminal vesicle by aglandular duct. Sinus-sac and THE HEMIUROIDEA 87 permanent sinus-organ present; of variable size. Ovary oval. Excretory arms not united inforebody. TYPE-SPECIES. Dinurus tornatus (Rudolphi, 1819) [by original designation]. ALLOSTOMACHICOLA Yamaguti, 1958 Ecsoma enormous. Body-surface smooth. Seminal vesicle elongate-oval; in forebody. Parsprostatica short; vesicular [? or long, tubular; see fig. 13b of Chauhan, 1954]; not connected toseminal vesicle by distinct aglandular duct. Sinus-sac present; small; oval. Permanent sinus-organ apparently absent. Ovary reniform; may be indistinctly lobed. Majority of uterus withinecsoma; normally fills more than half of ecsoma. Excretory arms (?) united in forebody. TYPE-SPECIES. Allo stomachic ola secundus (Srivastava, 1937) [by original designation].COMMENT. Stomachicola lepturusi Gupta & Gupta, 1976, appears to belong to this genus. ATHERIA Hafeezullah, 1975 Body-surface smooth. Seminal vesicle saccular; in forebody. Pars prostatica short, tubular; con-nected to seminal vesicle by short, aglandular duct. Sinus-sac present; elongate-oval. Permanentsinus-organ present; (?) long, muscular. Ovary oval. Distal extremity of uterus vesicular. Excre-tory arms united in forebody. TYPE-SPECIES. Atheria zakiae Hafeezullah, 1975 [by original designation]. COMMENT. This genus is apparently close to Erilepturus as a terminal dilation of the uterus occursin both genera, although it has not been reported in all species of Erilepturus. The differences inthe shape of the sinus-sac and in the length of the aglandular part of the pars prostatica are ofquestionable generic importance in this case; but we provisionally accept this genus on the basisof the distinct difference in the position of the seminal vesicle. ECTENURUS Looss, 1907 [t(w); n(w)] Magnacetabulum Yamaguti, 1934Parectenurus Manter, 1947 Body-surface with plications. Seminal vesicle saccular, tubular or divided into two or threesections; postero-dorsal to ventral sucker or in anterior hindbody. Pars prostatica short (?ormissing) ; connected to seminal vesicle by long, aglandular duct. Sinus-sac and permanent sinus-organ present; small. Ovary oval. Excretory arms not united in forebody. TYPE-SPECIES. Ectenurus lepidus Looss, 1907 [by original designation]. ERILEPTURUS Woolcock, 1935 [n(w)] Uterovesiculurus Skrjabin & Guschanskaja, 1954 Body-surface smooth (or finely transversely striated). Seminal vesicle variable; (?) oval, tubularto trilocular in the same species ; dorsal or postero-dorsal to ventral sucker. Pars prostatica short,tubular; connected to seminal vesicle by long, aglandular duct. Sinus-sac present; dilate proxi-mally (?or tubular). Permanent sinus-organ present; small. Ovary oval. Distal extremity ofuterus (outside sinus-sac) may be vesicular. Excretory arms united in forebody. TYPE-SPECIES. Erilepturus tiegsi Woolcock, 1935 [by original designation]. COMMENT. The vesicular nature of the terminal portion of the uterus, used by Skrjabin & Guschan-skaja (1954) to erect Uterovesiculurus, is also found in Erilepturus platycephali (Yamaguti, 1934)according to Manter (1970), and possibly in other species of this genus. It is not clear whetherthis is a transient feature. In some species, such as those described by Yamaguti (1970), theproximal dilation of the sinus-sac is apparently missing. 88 D. I. GIBSON & R. A. BRAY MECODERUS Manter, 1940 Anterior part of hindbody attenuated. Body-surface smooth. Seminal vesicle saccular; well backin hindbody, just anterior to testes. Pars prostatica in two parts, one anterior to and other pos-terior to attenuated part of body, connected by long, aglandular duct; not connected to seminalvesicle by distinct aglandular duct. Sinus-sac present; small, oval. Permanent sinus-organapparently absent. Ovary oval. Excretory arms united in forebody. TYPE-SPECIES. Mecoderus oligoplitis Manter, 1940 [by original designation]. COMMENT. There are certain morphological similarities between this genus and Stomachicolamagna (Manter, 1931). PARADINURUSViguems, 1958 [t(w,s)] Body-surface smooth. Seminal vesicle trilocular; at level of ventral sucker. Pars prostatica tubular;long; densely invested with gland-cells; connected to seminal vesicle by short, aglandular duct.Sinus-sac oval; thick-walled; relatively large. Permanent sinus-organ well developed. Ovary oval.Excretory arms not united in forebody. TYPE-SPECIES. Paradinurus manteri Vigueras, 1958 [by original designation]. (1) PROSTERRHURUS Fischthal & Kuntz, 1963 Body-surface smooth. Seminal vesicle trilocular; in hindbody. Pars prostatica long, tubular;densely surrounded by gland-cells; apparently not linked to seminal vesicle by distinct, aglandularduct. Sinus-sac short; tubular. Permanent sinus-organ present; small. Ovary oval. Excretoryarms ( ?). Parasitic in intestine of freshwater teleosts ( ? from estuarine region). TYPE-SPECIES. Prosterrhums labeonis Fischthal & Kuntz, 1963 [by monotypy]. COMMENT. The validity of this genus, which is based upon a single specimen, is questionable,because of shortcomings in its description and affinities with Erilepiurus. The details of theterminal genital apparatus are based upon figure 687 of Yamaguti (1971). According to Fischthal& Kuntz (1963), there is an elongate sinus-sac which encloses the distal ends of the pars prostaticaplus the metraterm, a prostatic vesicle, an ejaculatory duct and the hermaphroditic duct. STOMACHICOLA Yamaguti, 1934 Pseudo stomachicola Skrjabin & Guschanskaja, 1954Acerointestinecola Jahan, 1970Indostomachicola Gupta & Sharma, 1973 Ecsoma enormous. Body-surface smooth. Seminal vesicle oval; in hindbody. Pars prostaticatubular; long; sinuous; not connected to seminal vesicle by distinct aglandular duct; externalgland-cells may not be evenly distributed throughout length. Sinus-sac present; small; oval.Permanent sinus-organ absent or reduced to rudiment. Ovary oval to reniform. Majority ofuterine coils within ecsoma; normally fill less than half of ecsoma. Excretory arms united inforebody. TYPE-SPECIES. Stomachicola muraenesocis Yamaguti, 1934 [by original designation]. TUBULOVES1CULA Yamaguti, 1934 [n(s)] Lecithurus Pigulewsky, 1938 Body-surface smooth. Seminal vesicle tubular; sinuous; in hindbody. Pars prostatica with long,wide lumen; sinuous or straight; not connected to seminal vesicle by distinct aglandular duct.Sinus-sac present; oval. Permanent sinus-organ normally absent, but may occur as small papilla. THE HEMIUROIDEA 89 Ovary oval to round. Vitelline lobes tubular, but often stout. Excretory arms united in forebody.Parasitic in stomach, body-cavity and body-tissues of marine teleosts (also reported from intestineof sea-snake). TYPE-SPECIES. Tubulovesicula span' Yamaguti, 1934 [by original designation]. COMMENT. See Sinclair et al (1972) and Stunkard (1973) concerning Tubulovesicula v. Stomachicola.Several authors, such as Sogandares-Bernal (1959), consider T. lindbergi (Layman, 1930) to be asenior synonym of the type-species of this genus. Subfamily ELYTROPHALLINAE Skrjabin & Guschanskaja, 1954Musculovesiculinae Skrjabin & Guschanskaja, 1954 Ecsoma well developed. Body-surface smooth or plicated. Pre-somatic pit absent, but ventro-cervical groove often present. Testes tandem to symmetrical, usually oblique. Seminal vesiclewith exceptionally thick, muscular wall ; oval, not constricted into portions ; present in forebody,dorsal to ventral sucker or in hindbody. Pars prostatica tubular; long or short; usually linked toseminal vesicle by short, aglandular duct. Sinus-sac present; commonly tubular, long; not en-closing ejaculatory or prostatic vesicle. Sinus-organ usually well developed, but delicate andamuscular. Genital atrium usually deep (depending upon contraction). Ovary oval. Eggs rarelyfilamented. Vitellarium seven tubular to tear-shaped lobes, three on one side, four on the other,which may form rosette. Excretory arms united in forebody. Parasitic mainly in stomach ofmarine teleosts. Key to Elytrophallinae 1. A. Body-surface with plications ........... 2 B. Body-surface without plications .......... 4 2. A. Glandular region of pars prostatica mainly in hindbody ...... 3 B. Glandular region of pars prostatica in forebody CLUPENURUS 3. A. Sinus-sac long and narrow, reaching to the level of the seminal vesicle; vitelline lobes tear-shaped ELYTROPHALLOIDES B. Sinus-sac relatively long, but not reaching to level of seminal vesicle; vitelline lobes tubular LEC1THOCLADWM 4. A. Seminal vesicle in forebody; eggs may be filamented . . . MUSCULOVESICULAB. Seminal vesicle in hindbody; eggs not filamented .... ELYTROPHALLUS* ELYTROPHALLUS Manter, 1940 Body-surface smooth. Seminal vesicle small to large; in hindbody. Pars prostatica sinuous;mainly or entirely in hindbody. Sinus-sac long, tubular, thick-walled. Vitelline lobes tear-shapedto digitiform. Parasitic in stomach of marine teleosts. TYPE-SPECIES. Elytrophallus mexicanus Manter, 1940 [by original designation]. (?) CLUPENURUS Srivastava, 1935 Body-surface with plications. Testes symmetrical to oblique. Seminal vesicle compact, oval;in hindbody. Pars prostatica in forebody. Sinus-sac bulbous; small. Vitelline lobes tubular.Parasitic in stomach of migratory clupeid teleosts (in freshwater). TYPE-SPECIES. Clupenurus piscicola Srivastava, 1935 [by original designation]. COMMENT. The taxonomy of the hemiurid parasites of Hilsa (=Clupea; =Ilisha) ilisha is confused,as the descriptions of the species recorded either contain questionable features or are totally * Joliniophylhnn is inadequately described, but keys to this position. 90 D. I. GIBSON & R. A. BRAY inadequate. In addition to Clupenurus piscicola, the following species of hemiurid have been re-corded from this host: Lecithocladium ilishae Mamaev, 1970, nee Bashirullah & D'Silva, 1973. Lecithocladium ilishae Bashirullah & D'Silva, 1973, nee Mamaev, 1970. Lecithocladium chauhani Hafeezullah, 1975. Some of these descriptions indicate relationships with the elytrophallines and others with thedinurines; but the problem cannot be resolved until a comparative study of these forms, some ofwhich are probably synonymous, is undertaken. EL YTROPHALLOIDES Szidat, 1955 [T(w,s) ; t(w,s)] Body-surface with plications. Seminal vesicle large, reaching back to level of testes. Pars prosta-tica sinuous; in hindbody. Sinus-sac long, normally reaching back to level of seminal vesicle.Vitelline lobes tear-shaped. Parasitic in stomach of marine teleosts (in southern hemisphere). TYPE-SPECIES. Elytrophalloides oatesi (Leiper & Atkinson, 1914) [syn. E. merluccii Szidat, 1955 -type by original designation]. (l)JOHNIOPHYLLUMSkrjabm & Guschanskaja, 1954 [Inadequately described.] Body-surface smooth. Seminal vesicle small; in hindbody. Details ofsinus-sac and pars prostatica not known. Vitelline lobes digitiform. Parasitic in intestine of marineteleosts. TYPE-SPECIES. Johniophyllum johnii (Yamaguti, 1938) [by original designation]. LECITHOCLADIUM Lime, 1901 [t(w); n(w,s)] Body-surface with plications. Oral sucker often funnel-shaped. Pharynx elongate. Seminal vesiclelarge; in hindbody. Pars prostatica long and sinuous; mainly or entirely in hindbody. Sinus-sactubular; narrow; not reaching level of seminal vesicle and usually entirely or mainly in forebody.Vitelline lobes long and tubular. Parasitic in stomach of marine teleosts. TYPE-SPECIES. Lecithocladium excisum (Rudolphi, 1819) [by original designation]. MUSCULOVESICULA Yamaguti, 1940 Body-surface smooth. Seminal vesicle elongate; in forebody or overlapping ventral sucker. Parsprostatica short and indistinct; in forebody. Sinus-sac elliptical to pyriform; short. Vitelline lobesdigitiform. Eggs may be filamented. Parasitic in stomach of marine teleosts (eels). TYPE-SPECIES. Musculovesicula gymnothoracis Yamaguti, 1940 [by original designation]. Subfamily GLOMERICIRRINAE Yamaguti, 1958 Ecsoma well developed. Body-surface plicated. Pre-somatic pit absent. Testes oblique to tandem.Seminal vesicle bipartite; both parts globular to spindle-shaped; anterior part muscular; inhindbody or dorsal to ventral sucker. Pars prostatica tubular; short; linked to seminal vesicle byaglandular duct. Claviform sinus-sac present; in fore- or reaching into hindbody; enclosingprostatic vesicle. Hermaphroditic duct convoluted. Sinus-organ present; amuscular; long; con-voluted. Genital atrium well developed. Vitellarium two irregularly oval, symmetrical masses.Excretory arms united in forebody. Parasitic in stomach of maiine teleosts. GLOMERICIRRUS Yamaguti, 1937 [n(w,s)] Defined as subfamily.TYPE-SPECIES. Glomericirrus amadai Yamaguti, 1937 [by original designation]. THE HEMIUROIDEA 91 COMMENT. The interpretation of the terminal genitalia, based on our own sectioned material,differs markedly from the early descriptions (Yamaguti, 1937, 1938b). The observations ofManter (1970) and Campbell & Munroe (1977) agree with our interpretation. Subfamily HYPOHEPATICOLINAE Skrjabin & Guschanskaja, 1954 Body spindle-shaped. Ecsoma reduced; appears to be permanently withdrawn. Body-surfacesmooth. Presomatic pit absent. Gut-caeca end blindly. Testes symmetrical at level of middle orposterior margin of ventral sucker. Seminal vesicle anterior or antero-dorsal to ventral sucker;constricted into two portions; elongate saccular; may be sinuous. Pars prostatica short; slightlyvesicular; may be linked to seminal vesicle by short, aglandular duct. Sinus-sac present; oval;enclosing prostatic vesicle, part of metraterm and hermaphroditic duct. Permanent sinus-organabsent. Genital atrium present. Ovary oval. Much of uterus post-ovarian. Eggs with long, polarfilament. Vitellarium seven digitiform lobes (three on one side, four on the other), forming post-ovarian rosette. Excretory arms united in forebody. Parasitic under connective tissue membraneof liver and in gut of marine teleosts. HYPOHEPATICOLA Yamaguti, 1934 [t(w)] Defined as subfamily.TYPE-SPECIES. Hypohepaticola callionymi Yamaguti, 1934 [by original designation]. COMMENT. This representative of a monospecific subfamily was originally found under the con-nective tissue membrane of the liver, a very unusual habitat: it has also been recorded byYamaguti (1942) from the stomach of the type-host, Callionymus valenciennesi, and from theintestine of Monacanthus cirrhifer. Yamaguti states, The proper location of the worm may be thestomach of C. valenciennesi as is the case with one of the present examples, but in fact it occursmore frequently on the surface of the liver. M. cirrhifer may be an accidental host.' We haveexamined material from the liver of M, cirrhifer collected by Dr A. Ichihara from Sagami Bay,Japan, in 1966, and specimens were recorded from the liver of Callionymus flagris by Ichiharaet al. (1963), so it appears that the liver is the normal site of this parasite. In our conception of Hypohepaticola, we have interpreted Yamaguti's (1934) 'distal portion ofthe pars prostatica' as being a prostatic vesicle and his 'small receptaculum seminalis' as beingJuel's organ. In our view this genus is morphologically similar to the Lecithochiriinae, differingfundamentally according to the original description, only in the apparent absence of an ecsomaand the presence of filamented eggs. These two features are probably associated with the peculiarsite of this parasite, as the presence of an ecsoma would not be significantly advantageous underthe surface-membrane of the liver, whilst the presence of filaments on the eggs may aid theirevacuation from the tissues of the host. When we examined specimens from M. cirrhifer we could with some difficulty distinguish awithdrawn ecsoma. There is no evidence that this small structure is ever extruded. This suggeststhat Hypohepaticola is closely related to the Lecithochiriinae, especially as there is a tendency forthe reduction of the ecsoma to occur in the latter group. For the present, however, we haveretained the subfamily Hypohepaticolinae, because of the unusual habitat and the filamented eggs. Hypohepaticola andamanensis Gupta & Miglani, 1974, from 'a teleost marine fish' off India,appears, from the brief description given, to possess none of the definitive characters of this genus.Their later (1976) description suggests that it is a lecithasterid. Subfamily LECITHOCHIRIINAE Liihe, 1901 Sterrhurinae Looss, 1907 Brachyphallinae Skrjabin & Guschanskaja, 1955 Trithelaminae Yen, 1955 Tricotyledoniinae Skrjabin & Guschanskaja, 1957 Dissosaccinae Yamaguti, 1958 92 D. I. GIBSON & R. A. BRAY Ecsoma usually well developed, occasionally reduced. Body-surface usually smooth, but occasion-ally plicated or rugate. Muscular 'shoulder-pads' present or absent. Presomatic pit and ventro-cervical groove present or absent. Testes tandem to symmetrical, usually oblique. Seminalvesicle elongate; constricted into two portions, which are occasionally separated by a duct, ortubular and convoluted; in bipartite forms anterior half may have thicker wall; normally inforebody, but forms with halves separated by duct may extend into hindbody. Pars prostaticashort; vesicular or tubular; may extend slightly into base of sinus-sac; linked to seminal vesicleby short, aglandular duct. Sinus-sac present; rarely of 'open'-type; enclosing distinct ejaculatoryor prostatic vesicle and metraterm. Permanent sinus-organ absent. Genital atrium usually smallor absent, occasionally well developed. Ovary oval. Uterus mainly pre-ovarian or roughly equallydistributed in pre- and post-ovarian fields. Eggs without filaments. Vitellarium seven digitiformto oval lobes in lateral groups of three and four, or with tendency to become two distinct lateralmasses which often exhibit three and four lobes. Excretory arms united in forebody. Normallyparasitic in gut of marine teleosts. COMMENT. It is important to distinguish a prostatic (or ejaculatory) vesicle from a vesicular parsprostatica, otherwise difficulties of distinguishing some lecithochiriine and plerurine speciesbecome apparent. A prostatic (or ejaculatory) vesicle occurs entirely or mostly within a sinus-sacand together with a typical (external) pars prostatica from which it can be differentiated. In someplerurine genera which possess a recognizable sinus-sac, e.g. Synaptobothrium, the pars prostaticaextends into the base of the 'open' sinus-sac, but the region of the pars prostatica inside thesinus-sac is indistinguishable from the region outside. One could possibly divide the Lecithochiriinae into two groups: (1) those with a distinctly seven-lobed vitellarium; and (2) those with a vitellarium composed oftwo entire or indistinctly lobed masses. We feel that the two groups do grade into one another,as the lobation in some species of Lecithochirium is reduced, whilst three- and four-lobed vitellinemasses can be seen in some specimens of Brachyphallus. Some caution, therefore, should beexercised when using the key presented below. Key to Lecithochiriinae 1. A. Vitellarium 7 distinct oval to digitiform lobes 2 B. Vitellarium 2 entire masses which may be indistinctly 3- and 4-lobed .... 6 2. A. Large, muscular 'shoulder-pads' present ......... B. Large, muscular 'shoulder-pads' absent 4 3. A. Small accessory sucker present anterior to oral sucker . . . TRICOTYLEDON1AB. No small accessory sucker .... . CYATHOLECITHOCHIRIUM 4. A. Small muscular pad present anterior to oral sucker .... CATARINATREMAB. Pre-oral lobe only present anterior to oral sucker ....... 5 5. A. Large, eversible genital atrium present PL1CATRWM B. Normal small genital atrium present . . ... LECITHOCHIRIUM 6. A. Seminal vesicle composed of two parts separated by narrow duct and reaches into hindbody ............ . B. Seminal vesicle in forebody, tubular or bipartite, parts not separated by a duct. . . 8 7. A. Body-surface plicated anteriorly PSEUDODINOSOMA B. Body-surface smooth . DISSOSACCUS 8. A. Seminal vesicle bipartite; body-surface plicated; deep presomatic pit present BRACHYPHALLUSB. Seminal vesicle a wide, convoluted tube; body-surface smooth; presomatic pit absent; ecsoma reduced PROLECITHOCHIRIUM LECITHOCHIRIUM Luhe, 1901 [t(w,s); n(w,s)] Sterrhurus Looss, 1907 Ceratotrema Jones, 1933 Jajonetta Jones, 1933 Separogermiductus Skrjabin & Guschanskaja, 1955 THE HEMIUROIDEA 93 Magniscyphus Reid, Coil & Kuntz, 1965Neohysterolecitha Ahmad, 1977 Ecsoma well or poorly developed. Body-surface smooth. Pre-oral lobe rarely with two lateralknobs. Presomatic pit and/or ventro-cervical groove often present. Seminal vesicle bipartite,tripartite or occasionally coiled; in forebody. Pars prostatica tubular, with wide lumen, tovesicular. Short, narrow extension of pars prostatica and/or ejaculatory duct may be presentwithin sinus-sac. Ejaculatory (or prostatic) vesicle linked posteriorly to antero-dorsally with parsprostatica or ejaculatory duct. Temporary sinus-organ may form. Vitellarium two lateral masses;usually divided into three and four oval to digitiform lobes. Parasitic in gut (mainly stomach) ofmarine teleosts ; also recorded from body-cavity, hepatic ducts and gills of marine teleosts and(?) gut of freshwater reptiles. TYPE-SPECIES. Lecithochirium rufoviride (Rudolphi, 1819) [by original designation]. COMMENT. Sterrhurus is supposed to be distinguished from Lecithochirium by the absence of apresomatic pit (Lloyd, 1938; Manter & Pritchard, 1960a). The systematic significance of the pre-somatic pit has been discussed by Jones (1943) and Nasir & Diaz (1971). It appears to us thatobservations of this character have, in the past, not been careful enough. Many authors appearto have mistaken the ventro-cervical groove, which occurs commonly in this genus, for a preso-matic pit, with the result that some descriptions must remain questionable. For example, Nahhas& Short (1965) described specimens of Lecithochirium mesosaccum Manter, 1947, from Sciaenopsocellata with a presomatic pit and from Synodus foetans without. If this character is to be takenas distinguishing these two genera, it would appear that specimens from Sciaenops are notrepresentative of the same genus as those from Synodus. If we assume that Nahhas & Shortmistook the ventro-cervical groove, a structure with a transitory nature, for a presomatic pitwhich is a permanent structure (see p. 49), then the specimens can be considered synonymous.We have examined the type-species of Lecithochirium and can confirm that a small [comparedwith that of Brachyphallus and Synaptobothrium] presomatic pit is present. This is visible insections, but barely so in whole-mounts. We can also confirm that this structure is absent inLecithochirium musculus (Looss, 1907), the type-species of Sterrhurus. Considering its small sizein L. rufoviride and the questionable value of some of the information in the literature, we con-sider it to be inadvisable at present to distinguish these two genera on this feature, although futurework, involving the examination of many species in transverse sections, might show that it is avalid taxonomic criterion. Another feature used to distinguish Lecithochirium from Sterrhurus is the presence of a prostaticvesicle in the former and an ejaculatory vesicle in the latter (Crowcroft, 1946). The differencebetween these two types of vesicle is the presence of a lining of gland-cells in the case of theprostatic vesicle [we prefer to call the latter a glandular ejaculatory vesicle]. It appears, however,that these gland-cells can be lost, their concentration in one species varies and that they may infact be present or absent in the same species (Manter & Pritchard, 1960a; Nasir & Diaz, 1971).This feature, therefore, appears to be of little value, except as an aid to specific identification. Con-trary to the work of other authors, e.g. Jones (1943), in our sectioned material of L. rufoviridethere are no gland-cells lining the ejaculatory vesicle; but, as in the case of L. musculus, thedistal ends of some of the cells lining the pars prostatica do extend into the proximal extremityof the vesicle. Separogermiductus was distinguished from Lecithochirium in having 'a bulbous ejaculatoryvesicle, almost as large or even larger than the pharynx, lined with a refractive non-cellular wall,empty of cells or droplets, and into which the pars prostatica enters dorsally and anteriorly'(Manter & Pritchard, 1960a). We have had the opportunity of examining specimens of Lecitho-chirium genypteri Manter, 1954, which is considered by Manter & Pritchard (1960a) to be aspecies of Separogermiductus. The terminal genitalia are very much like those of our specimensof L. rufoviride. The ejaculatory vesicle is, perhaps, a little larger in L. genypteri, but the liningof the ejaculatory vesicle and the point of entry of the pars prostatica into this vesicle are verysimilar. In both cases the pars prostatica passes over the dorsal wall of the vesicle and enters 94 D. I. GIBSON & R. A. BRAY antero-dorsally. As Jones (1943) shows the point of entry in L. rufoviride to be almost directlydorsal, it seems certain that this character varies to some extent, and is not reliable as a genericcharacter. With regard to Magniscyphus, the 'cup- or bowl-shaped' forebody is merely a variation of theventro-cervical groove, which is common in many species of Lecithochiriwn (according to ourdefinition). Indeed, a similar condition can be seen in fig. 38 of Looss (1908), in which he figuresL. musculus. The occurrence of so-called prostatic cells around the hermaphroditic duct requireshistochemical confirmation, as this may have been a case of the misinterpretation of the smallgland-cells which commonly occur within the sinus-sac of hemiuroids. If these cells are prostatic,then it is more likely that they are associated with the distal extremity of the pars prostatica,which occasionally extends into the base of the sinus-sac. We do not consider that the presenceof these cells is sufficient reason to substantiate the existence of Magniscyphus as a distinct genusfrom Sterrhurus, and hence Lecithochiriwn. In their useful work on Lecithochirium, Nasir & Diaz(1971), in addition to including Sterrhurus, Separogermiductus and Magniscyphus as synonyms ofLecithochirium, also considered Synaptobothrium and Plerurus likewise. We believe that Nasir &Diaz (1971) went too far with their synonymies, and that Synaptobothrium and Plerurus are validgenera. BRA CH YPHALL US Odhner, 1 905 [t(w,s)] Body-surface plicated; plications may be crenulate. Presomatic pit present ; circular or oval; deep;glandular. Seminal vesicle bipartite; anterior part small, posterior part large; thin-walled;occurring mostly in forebody. Pars prostatica tubular. Temporary sinus-organ may be seen.Vitellarium two lateral masses; entire, irregularly lobed or indistinctly three- and four-lobed.Parasitic in gut (stomach) of marine and migratory teleosts. TYPE-SPECIES. Brachyphallus crenatus (Rudolphi, 1802) [by original designation], COMMENT. The terminal genitalia were described in detail by Lander (1904) and Slusarski (1958),and we agree that a glandular ejaculatory (prostatic) vesicle is present. CATAR1NATREMA Teixeira de Freitas & Santos, 1971 May bear papillae on ecsoma. Presomatic pit present. Muscular pad present anterior to oralsucker. Seminal vesicle bipartite; in forebody. Pars prostatica tubular. Vitellarium two masses ofthree and four short, digitiform lobes. Parasitic in stomach and intestine of marine teleosts. TYPE-SPECIES. Catarinatrema verrucosum Teixeira de Freitas & Santos, 1971 [by originaldesignation]. CYATHOLECITHOCHIRIUM Yamaguti, 1970 Body-surface smooth. Muscular 'shoulder-pads' present. Pre-oral accessory sucker absent.Seminal vesicle bipartite; anterior part with thick wall; in forebody. Pars prostatica may be partlywithin sinus-sac. Vitellarium seven digitiform lobes in two groups of three and four. Parasitic instomach of marine teleosts. TYPE-SPECIES. Cyatholecithochirium gymnothoracis Yamaguti, 1970 [by original designation]. DISSOSACCUS Manter, 1947 Ecsoma well developed. Body-surface smooth. Seminal vesicle in two parts separated by narrow duct; one part normally mainly anterior and other mainly posterior to ventral sucker. Pars prostatica (?) tubular. Vitellarium two slightly indented masses. Parasitic in stomach of marine teleosts. TYPE-SPECIES. Dissosaccus laevis (Linton, 1898) [by original designation]. THE HEMIUROIDEA 95 PLIC ATRIUM Manter & Pritchard, 1960 Papillae may occur on body-surface. Presomatic pit absent. Seminal vesicle bipartite; in forebody.Pars prostatica tubular. Large, eversible genital atrium present; wrinkled or convoluted wheneverted. Vitellarium seven digitiform lobes. Parasitic in intestine of marine teleosts. TYPE-SPECIES. Plicatrium lycodontis (Myers & Wolfgang, 1953) [by monotypy]. PROLECITHOCH1RWM Yamaguti, 1970 Ecsoma reduced. Body-surface smooth. Presomatic pit absent. Seminal vesicle tubular ; convolutedand widening posteriorly; in forebody. Pars prostatica tubular. Vitellarium two compact masses.Parasitic in stomach of marine teleosts. TYPE-SPECIES. Prolecithochirium pterois Yamaguti, 1970 [by original designation]. COMMENT. This genus has many of the characteristics of Lecithochirium ; but apparently lackslobation of the vitellarium. PSEUDOD1NOSOMA Yamaguti, 1970 Ecsoma well developed. Body-surface with crenulate plications (? giving 'scaley' appearance).Presomatic pit absent. Seminal vesicle in two parts separated by narrow duct; one part (convolu-ted) anterior and other (claviform) posterior to ventral sucker. Pars prostatica tubular. Vitellariumtwo slightly indented masses. Parasitic in stomach of marine teleosts. TYPE-SPECIES. Pseudodinosoma macrorchis Yamaguti, 1970 [by original designation]. TRICOTYLEDONIA Fyfe, 1954 [n(w,s)] Grassitrema Yeh, 1955 Body-surface smooth. Muscular 'shoulder-pads' present. Presomatic pit absent. Pre-oral accessorysucker present. Seminal vesicle bipartite; posterior part elongate; anterior to posterior margin ofventral sucker. Pars prostatica vesicular; partly enclosed by sinus-sac; leads into small, aglandularejaculatory vesicle; connected to seminal vesicle by short, aglandular duct. Vitellarium sevendigitiform lobes. Parasitic in stomach of marine teleosts. TYPE-SPECIES. Tricotyledonia genypteri Fyfe, 1954 [by original designation]. Subfamily LETHADENINAE Yamaguti, 1971 Ecsoma well developed. Body-surface smooth. Pre-somatic pit absent. Testes oblique. Seminalvesicle oval; thick-walled; in forebody. Pars prostatica vesicular; with muscular wall; externalgland-cells absent or weakly developed; separated from seminal vesicle by aglandular duct andfrom sinus-sac by long ejaculatory duct. Sinus-sac small; not containing ejaculatory or prostaticvesicle. Sinus-organ (?) present (? temporary) ; small. Genital atrium short. Vitellarium twosymmetrical, unlobed, oval masses. Excretory arms not united in forebody. Parasitic in stomachof marine teleosts. LETHADENA Manter, 1947Defined as subfamily.TYPE-SPECIES. Lethadena profunda (Manter, 1934) [by original designation]. PLERURINAE subfam. nov. Body small; spindle-shaped to cylindrical. Ecsoma reduced or well developed. Body-surfacesmooth, or occasionally with crenulate plications giving a scaley appearance. Presomatic pit 96 D. I. GIBSON & R. A. BRAY absent, except in Synaptobothrium. Prepharynx absent. Pharynx well developed. Oesophagusshort. 'Driisenmagen' present. Gut-caeca terminate blindly inside ecsoma. Testes pre-ovarian;symmetrical to tandem, usually oblique. Seminal vesicle elongate, saccular and constricted intotwo, three or four sections; thin-walled, although certain sections may have thicker walls; inforebody or partly in hindbody. Pars prostatica vesicular or tubular; may be partly enclosed bymuscles of sinus-sac; commonly linked to seminal vesicle by aglandular duct. Sinus-sac apparentlyabsent or poorly developed; when present usually of 'open'-type. Permanent sinus-organ absent.Ejaculatory (prostatic) vesicle absent. Hermaphroditic duct commonly vesicular proximally andtubular distally. Genital atrium usually deep, but may be shallow. Genital pore mid-ventral inforebody. Ovary entire or lobed. Laurer's canal absent. Canalicular and blind seminal receptaclesabsent. Juel's organ present. Uterine seminal receptacle present. Uterus convoluted; passing backfrom ovary into ecsoma and then forward into forebody. Vitellarium post-ovarian; composed oftwo, four- and three-lobed, masses; the lobes being small to digitiform. Excretory vesicle Y-shaped ; arms united in forebody. Parasitic in stomach of marine teleosts. COMMENT. It is important, in this group, to distinguish between a vesicular pars prostatica and anejaculatory (prostatic) vesicle. An ejaculatory vesicle occurs in the Lecithochiriinae, lacks externalprostatic cells, is normally entirely enclosed within a distinct sinus-sac, and is present togetherwith a normal pars prostatica which occurs externally to, or occasionally partly within, thesinus-sac. The vesicular pars prostatica of the Plerurinae varies from being completely outside thesinus-sac, if it is present, to being only partly enclosed by the muscles of a weakly developedsinus-sac of the 'open'-type. Key to Plerurinae 1. A. Seminal vesicle tripartite in forebody, anterior and middle sections with thick, muscular wall VOITREMA B. Seminal vesicle saccular to 4-lobed or tubular, thin-walled 2 2. A. Seminal vesicle in forebody 3 B. Seminal vesicle at least partly extended into hindbody ...... 4 3. A. Presomatic pit absent; vitelline lobes digitiform . ..... PLERURUS B. Presomatic pit present; vitelline lobes short .... SYNAPTOBOTHRIUM 4. A. Body-surface has 'scaley' appearance DINOSOMA B. Body-surface smooth ADINOSOMA PLERURUS Looss, 1907 [t(w,s)] Par apler urns Fischthal & Kuntz, 1963Merlucciotrema Yamaguti, 1971 Ecsoma reduced or well developed. Body-surface smooth. Testes symmetrical to oblique. Seminalvesicle in forebody; elongate; saccular, two-, three- or four-lobed; often sigmoid; thin-walled.Pars prostatica vesicular; may be linked to seminal vesicle by short aglandular duct (some authorsmaintain that this is a tubular region of the pars prostatica). Sinus-sac apparently absent or poorlydeveloped and of 'open'-type. Hermaphroditic duct tubular; deep; possibly eversible. Ovary ovalto lobed. Vitelline lobes tubular to digitiform. TYPE-SPECIES. Plerurus digitatus (Looss, 1899) [by original designation]. COMMENT. Yamaguti (1970) points out that Looss (1908) figures a large oval seminal receptaclein the type-species, and suggests that what Looss actually saw was a uterine seminal receptacle.We confirm that a uterine seminal receptacle does occur in this species. Juel's organ has beendescribed in P. longicaudatus (Yamaguti, 1953) by Madhavi & Rao (1974) and we have observedit in the type-species. Owing to its close phylogenetic relationship (see Fig. 9) with the Lecithochiriinae, we wonderedwhether the vesicular modification of the ejaculatory duct in this group might be a prostaticvesicle rather than a vesicular pars prostatica. Our observations of the type-species of this genusindicate that the structure present is a vesicular pars prostatica (see definition; p. 48). This is THE HEMIUROIDEA 97 not really surprising, if our suggestions as to its possible function are correct, because in theabsence of a sinus-sac, there is no functional requirement for a prostatic vesicle. We have included Merlucciotrema, which Yamaguti (1971) based upon Manter's specimenof Sterrhurus praeclarus Manter, 1934, as a synonym ofPlerurus, because it appears to differ onlyin the reduced nature of the ecsoma and in that the vitelline lobes appear to be separated bynarrow vitelline ducts. The size of the ecsoma is a variable feature in many hemiurid genera,even when contraction is taken into account, and Manter's original illustration suggests someevidence that the ecsoma of this species might be invaginated further than he indicates. ADINOSOMA Manter, 1947 Body-surface smooth. Testes oblique. Seminal vesicle large, saccular, bipartite; postero-dorsalto ventral sucker. Pars prostatica vesicular, but elongate; connected to seminal vesicle by long,aglandular duct. Sinus-sac apparently absent. Hermaphroditic duct long, with poorly developedhermaphroditic vesicle proximally. Ovary unlobed. Vitellarium two indented or lobed masses. TYPE-SPECIES. Adinosoma robustum (Manter, 1934) [by original designation]. COMMENT. This genus includes A. hawaiiense (Yamaguti, 1970) n. comb., a species which wasoriginally placed in the genus Dinosoma. DINOSOMA Manter, 1934 [T(w,s); n(w,s)] Body-surface with crenulate plications, giving 'scaley' appearance. Testes symmetrical to tandem.Seminal vesicle postero-dorsal to ventral sucker; saccular, bipartite or wide; sinuous. Parsprostatica vesicular; may be connected to seminal vesicle by long, aglandular duct. Sinus-sacapparently absent. Hermaphroditic duct long, narrow; with small vesicle proximally. Ovaryoval. Vitellarium two indented or lobed masses. TYPE-SPECIES Dinosoma rubrum Manter, 1934 [by original designation]. SYNAPTOBOTHRIUMvonLinstow, 1904 [t(w,s)] Body-surface smooth. Presomatic pit present; circular or oval; deep; glandular. Testes oblique.Seminal vesicle bipartite (? or tripartite); anterior part small, posterior part long; thin-walled;occurring mostly in forebody, but may extend dorsal to ventral sucker. Pars prostatica tubularwith wide lumen; may extend into base of sinus-sac. Sinus-sac weakly developed; of 'open'-type.Ovary oval. Vitellarium two lateral masses with three and four short lobes. Eggs may be reniform. TYPE-SPECIES. Synaptobothrium caudiporum (Rudolphi, 1819) [syn. S. copulans von Linstow,1904 - type by monotypy]. COMMENT. The sinus-sac in this genus is weakly developed and of the 'open'-type, and an ejacula-tory (prostatic) vesicle is absent. We have, therefore, included it in the Plerurinae. The wide parsprostatica may extend into the base of the 'open' sinus-sac. Lecithochirium apharei Yamaguti,1970, probably belongs to this genus. (?) VOITREMA Yamaguti, 1971 [Inadequately known.] Body-surface (?). Testes oblique. Seminal vesicle tripartite; in forebody;anterior and middle sections with thick, muscular wall. Pars prostatica vesicular; may be partlyenclosed by muscles of (?) sinus-sac; attached to seminal vesicle by short (?) aglandular duct.Sinus-sac (?) weakly developed; with diffuse musculature; of 'open'-type. Genital atrium sac-like.Ovary elongate oval. Vitelline lobes digitiform. TYPE-SPECIES. Voitrema amplum (Manter, 1961) [by original designation]. COMMENT. This is a questionable genus based upon one inadequately described specimen. 98 D. I. GIBSON & R. A. BRAY Subfamily PULMOVERMINAE Sandars, 1961 Ecsoma reduced. Body-surface smooth (? spines reported within suckers). Presomatic pit absent.Testes tandem to oblique. Seminal vesicle tubular; long; thick- walled; reaches to or almost tolevel of testes. Pars prostatica short; vesicular; partly enclosed by sinus-sac. Sinus-sac present;not enclosing ejaculatory or prostatic vesicle. Sinus-organ variable in length, (? temporary).Genital atrium small. Ovary occasionally divided into dorsal and ventral lobes. Vitellarium twolateral, closely aligned masses; normally with three and four lobes. Excretory arms united inforebody. Parasitic in lung of sea-snakes. PULMOVERMIS Coil & Kuntz, 1960 Hydrophitrema Sandars, 1960Laticaudatrema Telford, 1967 Defined as subfamily. TYPE-SPECIES. Pulmovermis cyanovitellosus Coil & Kuntz, 1960 [by original designation]. Family HIRUDINELLIDAE Dollfus, 1932 Botulidae Guiart, 1938Lampritrematidae Yamaguti, 1940Mediolecithidae Oshmarin, 1968[Includes: Profundiellinae Skrjabin, 1958] Body large; stout or elongate; contractile. Ecsoma absent. Body-surface smooth; may be papillatein forebody or wrinkled. Oral and ventral suckers well developed; latter in anterior half of body.Pharynx well developed. Oesophagus usually short. 'Driisenmagen' present. Gut-caeca terminateblindly or form uroproct; sometimes fuse subterminally forming cyclocoel; usually diverticulate.Testes two; in tandem, oblique or symmetrical; pre-ovarian; in hindbody. Seminal vesicletubular; normally thin- walled, occasionally partly thick- walled ; convoluted in forebody. Parsprostatica well developed; tubular; usually long. Ejaculatory duct long; muscular; surroundedby muscular 'cirrus-sac' ; opens into genital atrium through well-developed conical to cylindrical'cirrus'. Hermaphroditic duct, sinus-sac and sinus-organ absent. Genital atrium large; usuallycapable of being everted. Genital pore mid-ventral in forebody. Ovary oval; post-testicular; inmiddle or anterior half of hindbody. Laurer's canal and uterine seminal receptacle normallypresent. JuePs organ and blind or canalicular seminal receptacle absent. Uterus descendingventrally and ascending more dorsally; coiled mainly at level of vitellarium, but often extendingmore anteriorly into pre-ovarian region; mainly inter-caecal, occasionally reaching extra-caecally;metraterm opens into genital atrium directly or through a papilla-like organ situated immediatelyposterior to 'cirrus'. Eggs numerous; small; without filaments. Vitellarium composed of fromtwo to numerous long, straight or convoluted, branched tubules ; mainly post-ovarian ; inter- orextra-caecal. Excretory vesicle Y-shaped; arms initially dorso-ventrally oriented, convoluted,united in forebody. Parasitic in stomach (occasionally on gills) of large, carnivorous, marineteleosts. COMMENT. In our opinion this family contains three monotypic genera which cannot be dis-tinguished at the subfamily level. It is possible that Distoma gigas Nardo, 1827, from the stomachof Luvarus imperialis is a fourth genus; but, as suggested by Gibson & Bray (1977), there is someevidence that this species may be a sclerodistomid (see p. 113). Key to Hirudinellidae 1. A. Body stout, elongate or keyhole-shaped; uroproct present; 'cirrus-sac' small, globular; seminal vesicle entirely thin-walled ......... 2 B. Body slender, elongate; uroproct absent; 'cirrus-sac' large, elongate; distal part of seminal vesicle with muscular wall LAMPRITREMA THE HEMIUROIDEA 99 2. A. Vitellarium in two lateral fields between levels of testes and mid-hindbody; uterus mainly inter-caecal, post-ovarian, at level of vitellarium ..... HIRUDINELLAB. Vitellarium massed close to ventral surface, inter-caecal between ovary and posterior extremity; uterus reaching extra-caecally, mainly in anterior hindbody . . BOTULUS HIRUDINELLA de Blainville, 1828 [t(w,s)] Hirudinella Garcin, 1730 [Pre-Linnaean; see Gibson, 1976]Uroproctinella Skrjabin & Guschanskaja, 1957 Body stout, elongate or keyhole-shaped. Body-surface often transversely wrinkled. Uroproctpresent; gut-caeca may fuse sub-terminally in older specimens forming cyclocoel. Testes sym-metrical to oblique; in anterior hindbody. Seminal vesicle thin-walled throughout its length.'Cirrus-sac' relatively small; globular. 'Cirrus' cone-shaped to digitiform. Genital atrium capableof being everted through genital pore. Ovary in anterior hindbody. Uterus mainly inter-caecal;coils extending posteriorly from ovary to near posterior limit of vitellarium. Vitellarium in twolateral fields between testes and middle of hindbody. Parasitic in stomach of large carnivorous,marine teleosts (usually scombroids). TYPE-SPECIES. Hirudinella ventricosa (Pallas, 1774) [syn. H. clavata (Menzies, 1791) -type bymonotypy]. COMMENT. As discussed by Gibson (1976), it is likely that this genus is monotypic. BOTULUS Guiart, 1938 [T(w,s); t(w,s)] Profundiella A. S. Skrjabin, 1958Mediolecithus Oshmarin, 1968 Body normally stout. Uroproct present. Testes symmetrical to oblique; in anterior hindbody;large. Seminal vesicle thin-walled throughout its length; tubular and convoluted [or (?) globular(in Profundiella skrjabini A. S. Skrjabin, 1958)]. 'Cirrus-sac' small; globular. 'Cirrus' cone-shapedto digitiform. Genital atrium often everted through genital pore. Ovary in anterior hindbody.Uterus reaching extra-caecally in anterior hindbody. Vitellarium a densely tangled mass oftubeles in one ventral, inter-caecal field between ovary and posterior extremity. Parasitic instomach of large, carnivorous, marine teleosts (Alepisaurus) and (?) accidentally in piscivoroussharks. TYPE-SPECIES. Botulus microporus (Monticelli, 1889) [syn. B. alepidosauri Guiart, 1938 -type bymonotypy]. COMMENT. The two specimens of Botulus alepidosauri originally described by Guiart (1938),according to his manuscript, were in poor condition (they were dried out) which accounts for theinadequate description. We have been able to examine specimens of Botulus from the type-host,Alepisaurus ferox, and to refine the concept of this genus (see Gibson & Bray, 1977). We havealso examined the type-specimens of Distomum microporum Monticelli, 1889, present in thecollections of the British Museum (Natural History). These specimens were recovered from thetype-host (A. ferox) and type-locality (off Madeira) of B. alepidosauri. Although D. microporumhas been listed as a species of Hemiurus by some authors (Looss, 1899; Yamaguti, 1971), ourexamination has convinced us that it is a senior synonym of B. alepidosauri. The morphology ofBotulus microporus is described in detail elsewhere (Gibson & Bray, 1977). Profundiella was originally erected for a new species, P. skrjabini, from Alepisaurus aesculapius(which may be synonymous with A. ferox), in the Pacific Ocean by A. S. Skrjabin (1958). Thereappears to be no significant difference between this genus and Botulus, except for the reportedpresence of a globular seminal vesicle in the former. A second species, P. alepisauri, was describedby Parukhin & Nikolaeva (1967) from Alepisaurus sp. in the Gulf of Mexico (A. ferox appears tobe the only species of Alepisaurus recorded in this region); but this species possesses a seminalvesicle which is tubular and coiled. Examination of specimens of Botulus from Alepisaurus ferox 100 D. I. GIBSON & R. A. BRAY from off Miami Beach, Florida, show that they appear to be indistinguishable from B. microporus.It seems probable that the apparent globular seminal vesicle of P. skrjabini may in fact be atightly coiled, tubular form, as a tubular seminal vesicle is the normal condition in primitivehemiuroids. Stunkard (1965) also considered Profundiella as a synonym of Botulus, but it waslisted separately by Yamaguti (1971). In agreement with Parukhin & Nikolaeva (1974), we are of the opinion that Mediolecithuspacificus Oshmarin, 1968, belongs to Botulus. One specimen was described by Oshmarin fromLamna cornubica, a piscivorous shark. It is likely that this was an accidental infestation, asAlepisaurus is the normal host of Botulus. LAMPRITREMA Yamaguti, 1940 [T(s)] Hirudinelloides Gaevskaja & Kovaleva, 1977 Body elongate; slender. Papillae present on forebody. Uroproct absent. Testes in tandem; nearmiddle of hindbody. Most of seminal vesicle thin-walled, but distal portion forms thick-walled,muscular 'pars musculosa'. Thick-walled pars prostatica lies ventral to posterior portion of'cirrus-sac'. Male duct leads into 'cirrus-sac' some distance from its posterior extremity. 'Cirrus-sac' large; elongate; club-shaped. 'Cirrus' long or short; capable of being extruded some distancethrough genital pore. Genital atrium deep. Ovary near middle of hindbody. Laurer's canal (?)absent. Seminal receptacle (?) small; enclosed in Mehlis' gland [see below]. Uterus extends backto near posterior limit of vitellarium; mainly coiled inter-caecally in post- and pre-ovarian regionsof hindbody. Vitellarium a pair of lateral tubules with short dorsal branches; mainly extra-caecal ;passing posteriorly from ovary to about half-way to posterior extremity. Excretory arms appearto unite in forebody (cf. Yamaguti, 1940). Parasitic in stomach (? occasionally on gills) of marineteleosts (Lampris, Brama and Thyrsites). Immature forms recorded from salmonids (stomach,oesophagus or gills). TYPE-SPECIES. Lampritrema miescheri(Zschokke, 1890) [syn. L. nipponicum Yamaguti, 1940 - typeby original designation]. COMMENT. We considered separating Lampritrema from Hirudinella and Botulus at the subfamilylevel, but there are no morphological differences which one could definitely consider to beimportant at the subfamily level. Notwithstanding the descriptions of Lampritrema atlanticum Delyamure & Serdyukov, 1970,L. hawaiiense Yamaguti, 1970, and Hirudinelloides elongatus Gaevskaja & Kovaleva, 1977, weconsider this genus to be monotypic (see Gibson & Bray, 1977). L. savalai Zaidi & Khan, 1977,is clearly a hemiurid. Yamaguti (1940) stated that Laurer's canal was absent in Lampritrema nipponicum and that asmall seminal receptacle was present inside Mehlis' gland. We question the absence of Laurer'scanal in this species, as it is present in all other primitive hemiuroids, and the small size (up to105 urn) and location of the seminal receptacle suggests that its presence and nature is question-able: we would expect a uterine seminal receptacle to be present. Neither of these features werecommented upon by Margolis (1962) in his redescription of this species. Family ISOPARORCHIIDAE Travassos, 1922 Body large; stout; dorso-ventrally flattened. Ecsoma absent. Body-surface smooth. Oral andventral suckers small. Pharynx well developed. Oesophagus short. 'Drusenmagen' absent. Gut-caeca sinuous; terminate blindly near posterior extremity. Testes two; symmetrical; pre-ovarian;in anterior hindbody. Seminal vesicle small; thin-walled; tubular; winding in forebody. Parsprostatica tubular. Ejaculatory duct within sinus-sac. Sinus-sac weakly developed; composed ofdiffuse musculature. Hermaphroditic duct short; opens into genital atrium through stout sinus-organ. Genital atrium with pair of concentric folds in its wall; capable of being extruded throughgenital pore [see Fig. 2]. Genital pore mid-ventral in forebody. Ovary tubular; well posterior to THE HEMIUROIDEA 101 testes. Laurer's canal present; may be slightly dilated proximally forming small rudimentaryseminal receptacle. Uterine seminal receptacle present. Juel's organ and canalicular or blindseminal receptacle absent. Uterus pre-ovarian; mainly coiled in hindbody. Eggs numerous; small;non-filamented. Vitellarium tubular; with dendritic branches arising from about six collectingducts; post-ovarian. Excretory vesicle Y-shaped; arms come close together dorsal to pharynx,but do not unite. Parasitic in swim-bladder of physostomatous teleosts in freshwater (Asia andAustralasia). ISOPARORCHIS Southwell, 1913 [t(w,s)] Leptolecithum Kobayashi, 1915Defined as family. TYPE-SPECIES. Isoparorchis hypselobagri (Billet, 1898) [syn. /. trisimilitubis Southwell, 1913 - typeby original designation]. Family LECITHASTERIDAE Odhner, 1905Lobatovitelliovariidae Yamaguti, 1965 Body usually small; normally spindle-shaped, occasionally elongate. Ecsoma absent. Body-surface smooth. Oral and ventral suckers well developed; ventral sucker normally in anteriorhalf of body. Muscular flange or flanges may be present immediately posterior to ventral sucker.Pharynx well developed. Oesophagus usually short. 'Drusenmagen' normally present. Gut-caecausually terminate blindly, but occasionally unite forming cyclocoel. Presomatic pit and ventro-cervical groove absent. Testes two, occasionally one; in tandem; oblique or symmetrical; usually,but not always, pre-ovarian; in hindbody. Seminal vesicle generally thin-walled, occasionallymuscular; oval, tubular or constricted into portions; in fore- or hindbody. Pars prostatica usuallytubular, occasionally vesicular; may be linked to seminal vesicle by aglandular tube. Ejaculatoryduct long, short or absent. Hermaphroditic duct present. Ejaculatory (prostatic) vesicle absent.Sinus-sac usually present; well or poorly developed; occasionally absent. Permanent sinus-organnormally absent, but hermaphroditic duct is often protruded to form temporary sinus-organ.Genital atrium large, small or absent. Ovary usually post-testicular; oval or four- (occasionallythree-) lobed. Usually only blind seminal receptacle present (normally large, thick-walled andsituated dorsal or antero-dorsal to ovary) and Laurer's canal, Juel's organ and both uterine orcanalicular seminal receptacles absent; occasionally only Juel's organ and uterine seminalreceptacle present; rarely only Laurer's canal and canalicular seminal receptacle present. Uterusmainly post- to entirely pre-ovarian; main bulk rarely extends into forebody. Eggs numerous;small; rarely filamented. Vitellarium commonly seven-lobed; occasionally six, eight or doublethese numbers (sometimes branched) lobes often in rosette arrangement; usually immediatelypost-ovarian, occasionally pre-ovarian or at level of ovary. Excretory vesicle Y-shaped; armsunited in forebody or not. Parasitic in gut, especially intestine, of marine teleosts. Key to Lecithasteridae 1. A. Uterine seminal receptacle present HYSTEROLECITHINAE (p. 104) B. Uterine seminal receptacle absent .......... 2 2. A. Uterus entirely or almost entirely pre-ovarian; hermaphroditic duct appears to be continuation of uterus; Laurer's canal may be present . TRIFOLIOVARIINAE (p. 109)B. Uterus partly post-ovarian; hermaphroditic duct normal ...... 3 3. A. Muscular ventro-lateral flange or flanges present immediately posterior to ventral sucker QUADRIFOLIOVARIINAE (p. 108)B. Muscular ventro-lateral flange or flanges absent immediately posterior to ventral sucker . 4 4. A. Seminal vesicle in forebody or dorso-lateral to ventral sucker (in one or two species of Lecithaster it may extend into the anterior hindbody, but these can be distinguished from the macradeninines by the well-developed nature of the sinus-sac) ... 5 102 D. I. GIBSON & R. A. BRAY B. Seminal vesicle entirely in hindbody; pars prostatica and/or ejaculatory duct long; sinus-sac small or poorly developed; usually parasitic in Acanlhurus spp. MACRADENININAE (p. 105) 5. A. Sinus-sac relatively well developed ; vitellarium post-ovarian . LECITHASTERINAE (p. 102)B. Sinus-sac apparently absent; genital atrium sucker-like; vitellarium pre-ovarian PROLECITHINAE (p. 107) Subfamily LECITHASTERINAE Odhner, 1905Lecithophyllinae Skrjabin & Guschanskaja, 1954 Caeca terminate blindly. Testes two, occasionally one; pre-ovarian. Seminal vesicle in forebody,dorsal to ventral sucker or, occasionally, in anterior hindbody. Pars prostatica short to mediumin length. Ejaculatory duct absent or short. Sinus-sac well developed. Permanent sinus-organabsent. Ovary entire or four-lobed. Blind seminal receptacle normally large; usually dorsal toovary. Uterus reaches to post-ovarian region. Vitellarium seven (rarely six or eight) oval todigitiform lobes in rosette or two linked groups of three and four; immediately post-ovarian;occasionally antero-posteriorly oriented. Excretory arms united in forebody or not. Normallyparasitic in intestine or stomach of marine teleosts. Key to Lecithasterinae 1. A. Testis single MONORCHIAPONURUS B. Testes two .............. 2 2. A. Vitelline lobes tubular ...... QADRIANA (inadequately described) B. Vitelline lobes tear-shaped to globular ......... 3 3. A. Ovary lobed, usually with four lobes; vitelline lobes tear-shaped . . . LECITHASTERB. Ovary oval to globular; vitelline lobes globular ....... 4 4. A. Genital atrium present LECITHOPHYLLUM B. Genital atrium small or absent APONURUS LECITHASTER Liihe, 1901 [n(w,s)] Testes two; obliquely symmetrical; usually oval, but occasionally lobed. Seminal vesicle saccularto elongate and sinuous; in forebody, dorsal to ventral sucker or, occasionally, in anterior hind-body. Sinus-sac oval. Genital atrium short. Ovary normally four-lobed. Seminal receptaclelarge, globular; dorsal to ovary. Vitellarium a radiating mass of seven tear-shaped lobes. Excre-tory arms apparently not united in forebody. Parasitic in intestine of marine teleosts. TYPE-SPECIES. Lecithaster confusus Odhner, 1905 [by subsequent designation - Odhner, 1905]. COMMENT. Dawes (1947) lists Leptosoma Stafford, 1904 [nee Desmarest, 1825; nee Travassos,1920; etc.; etc.] as a synonym of Lecithaster; but Stafford's description of Leptosoma obscurumis not adequate for a determination, even at the family-level. For this reason, therefore, andbecause: (1) Leptosoma was not mentioned by Miller (1941), who studied Stafford's material; (2)there are no specimens amongst Stafford's material in the National Museums of Canada, Ottawa;and (3) lecithasterids do not appear to be normal parasites ofLophius, from which Leptosoma wasrecorded ; we consider that this genus is unrecognizable. APONURUS Looss, 1907 Brachadena Linton, 1910 (?) Mordvilkoviaster Pigulewsky, 1938 Testes two; tandem to oblique. Seminal vesicle saccular; in forebody or occasionally dorsal toventral sucker. Hermaphroditic duct usually tubular, occasionally bipartite. Sinus-sac oval to THE HEMIUROIDEA 103 elongate-oval. Genital atrium absent, or occasionally small. Ovary oval or globular. Seminalreceptacle small to large; (?) ventral or dorsal to anterior region of ovary. Vitellarium usuallyseven globular to slightly elongate lobes; in lateral, occasionally antero-posteriorly oriented,groups of three and four. Excretory arms united in forebody. Parasitic in stomach (occasionallyintestine) of marine teleosts. TYPE-SPECIES. Aponurus laguncula Looss, 1907 [by monotypy]. COMMENT. The validity of Aponurus as a distinct genus from Lecithophyllum has been a matter ofsome discussion (see Margolis, 1958). The two genera differ in the presence and absence of adistinct genital atrium. As this is a contractile organ, its use as an important taxonomic criterionshould be treated with caution. In this case the character does appear to be of value, as it is adeep and apparently consistent feature in species of Lecithophyllum. It would not be surprising,however, if future workers discovered that, with regard to this feature, the two genera tend tograde into one another: indeed, Lecithophyllum hawaiiense Yamaguti, 1970, may be such a casein point. Yamaguti (1953) used the nature of the hermaphroditic duct to distinguish these twogenera : species of Lecithophyllum normally possess an hermaphroditic duct which is bipartite,whereas in Aponurus it is supposed to be uniform throughout its length. Yamaguti's (1970)figure of Aponurus acanthuri Manter & Pritchard, 1960, which he placed in Lecithophyllum despitethe extremely small size of the genital atrium, and Overstreet's (1973) figure of A. pyriformis(Linton, 1910) indicate that these species have bipartite hermaphroditic ducts. With regard to the status of Brachadena Linton, 1910, Yamaguti (1953, 1958, 1971) consideredthis genus a synonym of Lecithophyllum, whereas Margolis (1958) believed it to be distinct onthe basis of a central union of the vitelline lobes. Contrary to the work of Fischthal & Kuntz(1964c), which showed that a small genital atrium is present in the type-species, B. pyriformisLinton, 1910, Overstreet (1973) demonstrated that there is no distinct genital atrium present:Yamaguti's (1971) figure of the paratype also indicated that there is no genital atrium present.Overstreet's work showed that the type-species has an antero-posteriorly oriented vitellarium,the three- and four-lobed groups of which being united by a short duct. In view of the question-able validity of Aponurus itself, we feel that any variations in the nature and orientation of thevitellarium and in the hermaphroditic duct of Brachadena pyriformis, as compared with otherspecies of Aponurus, should be regarded as being of only specific value. Aponurus priacanthi Yamaguti, 1970, does not appear to be a lecithasterine. A uterine seminalreceptacle and possibly a Juel's organ are shown in Yamaguti's figure of this species. We have tentatively included Mordvilkoviaster Pigulewsky, 1938, as a synonym of Aponurus,as both Looss (1908) and Pogoreltseva (1952) have described Lecithaster galeatus Looss, 1907,the type-species, as having a round ovary. Skrjabin & Guschanskaja (1954) and Yamaguti (1971)consider Mordvilkoviaster to be a synonym of Dichadena Linton, 1910; but we believe that thesinus-sac is too well developed, the seminal vesicle too anterior and the pars prostatica too shortfor it to be considered a macradeninine. LECITHOPHYLLUM Odhner, 1905 [t(w,s)] Testes two; obliquely tandem to symmetrical. Seminal vesicle saccular; in forebody or dorsal toventral sucker. Hermaphroditic duct apparently bipartite. Sinus-sac elongate. Genital atriumpresent; generally deep. Ovary oval or globular. Seminal receptacle large; dorsal to ovary.Vitellarium seven globular lobes, in lateral groups of three and four. Excretory arms united inforebody. Parasitic in stomach of marine teleosts. TYPE-SPECIES. Lecithophyllum botryophoron (Olsson, 1868) [by original designation]. COMMENT. Brinkmann (1977), in his detailed redescription of the type-species, described andfigured a sinus-organ. As with other species in this family, this structure is temporary: it is notpresent in our material of this species (fixed in glacial acetic acid). A temporary sinus-organ,however, can be extruded in artificially relaxed, slowly fixed or frozen material. 104 D. I. GIBSON & R. A. BRAY (?) MONORCH1APONURUS Fischthal & Nasir, 1974 Testis single. Seminal vesicle saccular; in forebody. Sinus-sac elongate. Hermaphroditic ducttubular. Genital atrium absent. Ovary oval. Seminal receptacle pre-ovarian; postero-dextral totestis. Vitellarium seven globular lobes. Parasitic in intestine of marine teleosts. TYPE-SPECIES. Monorchiaponurus hemirhamphi Fischthal & Nasir, 1974 [by original designation]. COMMENT. This genus is known from only one specimen. As the absence of one testis is not arare feature amongst bi-testicular digeneans, it is possible that this specimen is merely anabnormal example of Aponurus. More specimens, as in the case of Monorchimacradena Nahhas& Cable, 1964, are required before this genus can be fully accepted. In listing this genus inde-pendently of Aponurus, we are assuming that the seminal receptacle, which is rather far anteriorfor a lecithasterid, has not been confused with the second testis. (?) QADRIANA Bilqees, 1971 [Inadequately described.] Testes two; tandem; postero-lateral to ventral sucker. Seminal vesiclesaccular; in forebody. Ovary oval. 'Seminal receptacle not obvious.' Vitellarium 'composed ofseveral tubes'. Uterus extra-caecal in hindbody. Parasitic in stomach of marine teleosts. TYPE-SPECIES. Qadriana fusiformis Bilqees, 1971 [by monotypy]. Subfamily HYSTEROLECITHINAE Yamaguti, 1958 Body small; elongate to spindle-shaped. Ventral sucker in middle or anterior half of body.Gut-caeca end blindly near posterior extremity. Testes two; oval; symmetrical to obliquelytandem; pre-ovarian; in anterior half of hindbody. Seminal vesicle usually tubular, occasionallyelongate saccular; in forebody. Pars prostatica usually tubular, occasionally vesicular; short.Sinus-sac present; often weakly developed; occasionally of open-type. Permanent sinus-organabsent; temporary sinus-organ may form. Hermaphroditic duct present within sinus-sac. Genitalatrium small or absent. Ovary oval; in anterior or posterior half of hindbody. Laurer's canal andblind or canalicular seminal receptacle absent. Juel's organ and uterine seminal receptacle present[see below]. Uterus almost entirely in hindbody; mainly pre- to mainly post-ovarian. Eggs withor without filaments. Vitellarium seven (occasionally eight) oval to digitiform lobes; post-ovarian.Excretory arms united in forebody or not. Parasitic mainly in intestine or stomach of marineteleosts (usually perciform genera, especially acanthurids and pomacentrids). COMMENT. There appears to have been some confusion between the genera of this subfamily andcertain other lecithasterid genera. We have, therefore, taken our definitions only from species inwhich the presence of a uterine seminal receptacle or the absence of a blind or canalicular seminalreceptacle has been indicated. Although Juel's organ has not been reported previously in thisgroup, we found it to be well developed in a paratype specimen of Hysterolecitha elongata Manter,1931, from the H. W. Manter Collection, which Dr M. H. Pritchard kindly allowed us to section.Yamaguti (1934) in his description of Hysterolecithoides epinepheli referred to a large seminalreceptacle in addition to a uterine seminal receptacle, and in his (1942) description of Hystero-lecitha nahaensis he referred to a small seminal receptacle in addition to a uterine seminalreceptacle. Unless a similar variation to that present in the Derogeninae occurs in this subfamily,it is probable that the organ described by Yamaguti as a seminal receptacle is Juel's organ. Key to Hysterolecithinae 1. A. Eggs filamented THULINIA B. Eggs without filaments ............ 2 2. A. Excretory arms united in forebody; uterus mainly pre-ovarian . . HYSTEROLECITHAB. Excretory arms not united in forebody; uterus mainly post-ovarian HYSTEROLECITHOIDES THE HEMIUROIDEA 105 COMMENT. In order to identify a genus from this subfamily, it is essential that eggs are teasedfrom the body and that the anterior regions of the excretory system are examined. The latternormally necessitates sectioning. It is clear, in species where the excretory system has not beenfully described, that there has been some confusion between Hysterolecitha and Hysterolecithoides.For example, although the excretory system was not fully described, Yamaguti (1971) placedHysterolecithoides pseudorosea Bravo-Hollis, 1956, in the genus Hysterolecitha, despite theposition of the ovary and the distribution of the uterus which suggested that Bravo-Hollis (1956)was correct. HYSTEROLECITHA Union, 1910 [n(w,s)] Ventral sucker usually in anterior half of body ; occasionally near middle. Seminal vesicle normallytubular; occasionally elongate saccular. Pars prostatica tubular; occasionally vesicular. Sinus-sacpresent; often weakly developed; may be of 'open'-type. Ovary normally in posterior half ofhindbody; normally separated from testes by loops of uterus. Uterus usually mainly pre-ovarian;(?) occasionally mainly post-ovarian. Eggs without filaments. Excretory arms united in forebody. TYPE-SPECIES. Hysterolecitha rosea Linton, 1910 [by original designation]. HYSTEROLECITHOIDES Yamaguti, 1934 Ventral sucker in middle of body. Seminal vesicle tubular. Pars prostatica tubular or vesicular.Sinus-sac oval. Ovary close to testes. Uterus mainly post-ovarian. Eggs without filaments.Excretory arms not united in forebody. TYPE-SPECIES. Hysterolecithoides epinepheli Yamaguti, 1934 [by original designation]. THULINIA gen. nov. Body elongate. Ventral sucker in anterior half of body. Gut-caeca end blindly near posteriorextremity. Testes two; oval; obliquely tandem; separated from ventral sucker and ovary byloops of uterus. Seminal vesicle tubular; in forebody; may reach dorsally to ventral sucker. Parsprostatica tubular; short. Sinus-sac present; well developed. Permanent sinus-organ absent;temporary sinus-organ may form. Hermaphroditic duct present within sinus-sac. Genital atriumsmall. Genital pore mid-ventral near middle of forebody. Ovary oval ; in posterior half of hind-body. Laurer's canal presumed absent. Canalicular or blind seminal receptacle absent. Juel'sorgan and uterine seminal receptacle presumed present. Uterus almost entirely in hindbody;coiled in pre- and post-ovarian fields. Eggs filamented (one filament at each end). Vitellariumseven (or eight) digitiform lobes; post-ovarian. Excretory vesicle Y-shaped; excretory armsunited in forebody. Parasitic in intestine of marine teleosts. TYPE-SPECIES. Thulinia tinkeri (Manter & Pritchard, 1960) n. comb. COMMENT. We have erected this genus because of the presence of filaments on the eggs, a featurewhich we believe to be a good generic criterion. It is named after Mr Jan Thulin, University ofGothenburg, who has helped us with several aspects of our work. Subfamily MACRADENININAE Skrjabin & Guschanskaja, 1954 Gut-caeca usually end blindly, but cyclocoel sometimes present. Testes two, occasionally one;oval; usually pre-ovarian, but may be at level of ovary or post-ovarian. Seminal vesicle in hind-body; saccular, tri-partite or tubular. Pars prostatica tubular; long. Ejaculatory duct usuallylong, but may be short or absent. Sinus-sac present; small; may be poorly developed. Permanentsinus-organ absent. Ovary four-lobed or oval. Blind seminal receptacle present. Uterus reachesto post-ovarian region. Vitellarium immediately anterior, at level of or immediately posterior toovary; variable, commonly six- to eight-lobed, but may be seven branched lobes, or twelve or 106 D. I. GIBSON & R. A. BRAY fourteen lobes, and group of lobes may be antero-posteriorly oriented. Excretory arms united inforebody or not. Parasitic in intestine or stomach of marine teleosts (normally Acanthurus spp.). Key to Macradenininae 1. A. Vitellarium consisting of 6 to 8 (usually 7) tear-shaped or slightly branched lobes; seminal vesicle saccular (? or tubular) 2 B. Vitellarium consisting of 12 or more lobes (occasionally 7 basic lobes divided into about40 secondary lobes) which may be tubular or globular; seminal vesicle tubular ortri-partite .............. 5 2. A. Ovary 4-lobed . . . PSEUDODICHADENA B. Ovary unlobed . 3 3. A. Testis single MONORCHIMACRADENA B. Testes 2 4 4. A. Testes at level of ovary; vitellarium antero-lateral to ovary; seminal vesicle (?) saccular or (?) tubular DICHADENA B. Testes pre-ovarian; vitellarium post-ovarian; seminal vesicle saccular (? with constriction) NEODICHADENA 5. A. Seminal vesicle tubular; vitelline lobes elongate, in single group ..... 6B. Seminal vesicle tri-partite; vitelline lobes globular, in 2 groups, 7 anterior and 7 posterior to ovary ACANTHURITREMA 6. A. Testes post-ovarian; vitellarium 12 claviform lobes, ventral to ovary . MACRADENINAB. Testes pre-ovarian; vitellarium essentially 7 lobes, but divided into about 40 secondary lobes, between ovary and seminal vesicle ...... MACRADENA COMMENT. We have retained all of the genera in this subfamily because of conflicting accountsof their morphology and in view of Yamaguti's (1971) examination of many of the holotypes;but it is likely that some of these forms will prove to be synonymous. Several of the genera requirethe study of fresh material before their validity can be confirmed, and a redescription of Dichadenaacuta Linton, 1910, especially is needed. This subfamily appears to be almost entirely restrictedto fishes of the genus Acanthurus from the central American region and Hawaii. MACRADENINA Manter, 1947 Cyclocoel not reported. Testes tandem; post-ovarian. Seminal vesicle tubular; loosely coiled atlevel of ovary. Pars prostatica long. Ejaculatory duct (?) absent. Sinus-sac sub-cylindrical; maybe incomplete posteriorly; appears to be protrusible. Ovary four-lobed; well forward in hindbody.Seminal receptacle globular; large; post-ovarian. Vitellarium twelve claviform, unbranchedtubules; ventral to ovary. Excretory arms (?). TYPE-SPECIES. Macradenina acanthuri Manter, 1947 [by original designation]. ACANTHURITREMA Yamaguti, 1970 Cyclocoel not reported. Testes tandem to oblique; pre-ovarian. Seminal vesicle tri-partite;posterior part large and spherical, middle part elongate elliptical, anterior part pyriform; con-nected to pars prostatica by aglandular duct; in anterior hindbody. Pars prostatica short.Ejaculatory duct absent. Sinus-sac thin, membranous; indistinct. Ovary four-lobed. Seminalreceptacle large; antero-dorsal to ovary. Vitellarium fourteen globular lobes; seven anterior andseven posterior to ovary. Excretory arms not united in forebody. TYPE-SPECIES. Acanthuritrema multivitellosum Yamaguti, 1970 [by original designation]. DICHADENA Linton, 1910 Cyclocoel (?) not reported (except in key by Yamaguti, 1971). Testes tandem; dorsal to ovary.Seminal vesicle sac-like (tubular according to Yamaguti, 1971); immediately pre-testicular. Pars THE HEMIUROIDEA 107 prostatica long; dilate posteriorly. Ejaculatory duct similar in length to pars prostatica. Sinus-sacoval. Ovary oval [four-lobed according to Manter, 1947: specimens with four-lobed ovarydescribed by Siddiqi & Cable, 1960, as D. acuta, now placed in Pseudodichadena]. Seminalreceptacle between posterior margin of ovary and posterior testis. Vitellarium six or sevenrounded to tear-shaped lobes; antero-lateral to ovary. Excretory arms (?). TYPE-SPECIES. Dichadena acuta Linton, 1910 [by original designation]. MACRADENA Linton, 1910 Cyclocoel not reported. Testes tandem; pre-ovarian. Seminal vesicle tubular; coiled in anteriorhindbody. Pars prostatica long. Ejaculatory duct about one quarter length of pars prostatica.Sinus-sac weakly developed and small. Ovary four ovoid lobes. Seminal receptacle large; oval;immediately posterior to ovary. Vitellarium originates between ovary and seminal receptacle;consists of seven main radial lobes which are finely divided to form about forty fairly short,tubular lobes. Excretory arms united in forebody. TYPE-SPECIES. Macradena perfecta Linton, 1910 [by original designation]. MONORCHIMACRADENA Nahhas & Cable, 1964 Cyclocoel not reported. Testis single; immediately pre-ovarian. Seminal vesicle sac-like; im-mediately pre-testicular. Pars prostatica and ejaculatory duct about equal in length. Sinus-sacspherical to pyriform; small. Ovary oval. Seminal receptacle as large or larger than ovary; dorsalto ovary. Vitellarium seven digitiform or slightly branched lobes; united centrally; post-testicular.Excretory arms united in forebody. TYPE-SPECIES. Manor chimacradena acanthuri Nahhas & Cable, 1964 [by original designation]. NEO DICHADENA Yamaguti, 1971 Cyclocoel not reported. Testes oblique; immediately pre-ovarian. Seminal vesicle sac-like (mayhave constriction). Pars prostatica long. Ejaculatory duct about half length of pars prostatica.Sinus-sac small; spherical. Ovary oval. Seminal receptacle large; lateral to ovary. Vitellariumabout eight tear-shaped lobes; post-ovarian. Excretory arms united in forebody. TYPE-SPECIES. Neodichadena acanthuri (Siddiqi & Cable, 1960) [by original designation]. PSEUDODICHADENA Yamaguti, 1971 Cyclocoel present. Testes small ; tandem ; at level of ovary. Seminal vesicle elliptical ; dorsal atlevel of gonads. Pars prostatica long. Ejaculatory duct short. Sinus-sac oval. Ovary four-lobed.Seminal receptacle post-ovarian. Vitellarium seven tear-shaped lobes; antero-lateral to ovary.Excretory arms united in forebody. TYPE-SPECIES. Pseudodichadena lobata Yamaguti, 1971 [syn. Dichadena acuta of Siddiqi & Cable,1960, nee Linton, 1910] [by original designation]. Subfamily PROLECITHINAE Yamaguti, 1971Folliovitellotrematinae Gupta & Sharma, 1972 (sic) Body spindle-shaped. Ventral sucker large, prominent. Cyclocoel present. Testes two; diagonalto symmetrical; at level of or slightly posterior to ventral sucker. Seminal vesicle saccular; inforebody. Pars prostatica short; vesicular. Sinus-sac and permanent sinus-organ absent. Large,spherical genital atrium present with muscular walls forming sucker-like structure (it is possiblethat this structure is an hermaphroditic duct surrounded by the remains of a sinus-sac). Ovarythree- to four-lobed; near posterior extremity; overlying cyclocoel. Blind seminal receptacle 108 D. I. GIBSON & R. A. BRAY posterior to ovary; at posterior extremity of body. Uterus mainly anterior to gonads. Vitellariumseven rounded lobes; immediately pre-ovarian; close to testes. Excretory arms not united inforebody. Parasitic in intestine of marine teleosts (Belonidae). PROLECITHA Manter, 1961 Lobatovitelliovarium Yamaguti, 1965Follicovitellosum Gupta & Sharma, 1972 As subfamily. TYPE-SPECIES. Prolecitha obesa Manter, 1961 [by original designation]. Subfamily QUADRIFOLIOVARINAE Yamaguti, 1970 Body elongate to spindle-shaped. Muscular ventro-lateral flange or flanges present immediatelyposterior to ventral sucker. Caeca usually terminate blindly, but cyclocoel may be present.Testes two; pre-ovarian. Seminal vesicle in hindbody; saccular, constricted into portions ortubular. Pars prostatica usually short; tubular; in hindbody. Ejaculatory duct long; may be linedwith cuticular villi. Sinus-sac oval. Permanent sinus-organ absent. Genital atrium short orapparently absent. Ovary oval or four-lobed. Blind seminal receptacle normally large; anterioror antero-dorsal to ovary. Uterus reaches to post-ovarian region. Vitellarium seven post-ovarian,claviform or oval lobes, or two groups of six to seven digitiform lobes, one pre-ovarian and onepost-ovarian. Excretory arms united in forebody. Parasitic in stomach or pyloric caeca ofacanthurid marine teleosts. COMMENT. This subfamily is morphologically similar to the Macradenininae, differing funda-mentally only in the presence of muscular flanges just posterior to the ventral sucker and in thelength of the pars prostatica. It is worth noting that all of the macradeninine and quadrifolio-variine genera are parasitic in acanthurid teleosts. Key to Quadrifoliovariinae 1. A. Muscular ventro-lateral flange present on one side of body only; cyclocoel present UNILACINIAB. Muscular ventro-lateral flanges symmetrical; cyclocoel absent ..... 2 2. A. Ovary 4-lobed; vitelline lobes in 2 antero-posteriorly oriented groups Q UA DRI FOLIO VA RWMB. Ovary oval; vitelline lobes in one group ....... BILAC1N1A QUADRIFOLIOVARIUMYamaguti, 1965 Pair of muscular ventro-lateral flanges immediately posterior to ventral sucker. Cyclocoel notreported. Testes tandem. Seminal vesicle a wide, convoluted tube; narrowing anteriorly. Parsprostatica short. Ejaculatory duct two to three times length of pars prostatica. Hermaphroditicduct convoluted; may be everted to form temporary sinus-organ. Sinus-sac thin-walled; ellipticalto oval. Ovary four-lobed. Vitellarium in two antero-posteriorly oriented rosette-like groups;one pre- and one post-ovarian; united by collecting duct; each group has six or seven digitiformlobes. Parasitic in stomach and pyloric caeca of marine teleosts (Naso). TYPE-SPECIES. Quadrifoliovarium pritchardae Yamaguti, 1965 [by original designation]. BILAC1N1A Manter, 1969Holacanthitrema Yamaguti, 1970 Pair of bilobed, muscular ventro-lateral flanges; symmetrical; immediately posterior to ventralsucker. Cyclocoel not reported. Testes tandem to oblique. Seminal vesicle convoluted, wide and THE HEMIUROIDEA 109 tubular or divided into four to five portions. Pars prostatica sigmoid. Ejaculatory duct one quarterto nearly equal length of pars prostatica. Hermaphroditic duct wide; straight. Sinus-sac oval;thin-walled. Ovary oval. Vitellarium seven rounded to claviform lobes; immediately post-ovarian.Parasitic in stomach and pyloric caeca of marine teleosts (Naso and Holacanthus}. TYPE-SPECIES. Bilacinia australis Manter, 1969 [by original designation]. U NIL ACINI A Manter, 1969 Bilobed muscular flange lateral to ventral sucker, on one side only. Cyclocoel present. Testesoblique. Seminal vesicle saccular; antero-dorsal to anterior testis. Ejaculatory duct twice lengthof pars prostatica. Hermaphroditic duct wide. Sinus-sac broadly ovoid. Ovary oval. Vitellariumseven short, digitiform lobes; postero-ventral to ovary. Parasitic in stomach of marine teleosts(Naso). TYPE-SPECIES. Unilacinia asymmetrica Manter, 1969 [by original designation]. Subfamily TRIFOLIOVARIINAE Yamaguti, 1958 Body cylindrical; long and thin, fusiform or elongate oval. Ventral sucker present well insideanterior half of body. Gut-caeca terminate blindly; often wide. Testes two; pre-ovarian inanterior hindbody; separated from ovary by many loops of uterus. Seminal vesicle in forebody,at level of ventral sucker or in hindbody; tubular, moniliform or elongate oval. Pars prostaticashort; tubular or vesicular. Ejaculatory duct short; enters hermaphroditic duct, which is con-tinuation of uterus, laterally. Sinus-sac present surrounding hermaphroditic duct; weak andmembranous; tubular or oval. Permanent sinus-organ absent. Genital atrium absent or small.Female reproductive complex close to posterior extremity. Ovary four-lobed. Laurer's canalpresent or absent. Seminal receptacle large; blind or canalicular; dorsal or antero-dorsal toovary. Uterine seminal receptacle and Juel's organ absent. Uterus entirely or almost entirelypre-ovarian; coils confined to hindbody. Eggs without filaments. Vitellarium seven or eightclaviform or digitiform lobes, which may be bilobed or irregularly branched distally; at level ofovary or immediately post-ovarian. Excretory arms united in forebody. Parasitic in intestine ofmarine teleosts. Key to Trifoliovariinae 1. A. Body long and thin; seminal vesicle in hindbody or dorsal (to antero-dorsal) to ventral sucker, elongate oval (to tubular and sinuous); vitelline lobes claviform, unbranched,in rosette arrangement ; Laurer's canal present .... TRIP OLIO VARIUMB. Body elongate oval to fusiform; seminal vesicle in forebody or antero-dorsal to ventralsucker, tubular, moniliform or elongate oval; Laurer's canal absent [or at least notreported] .............. 2 2. A. Seminal vesicle elongate oval ; vitellarium a rosette of 12 to 16 lobes (possible ca. 7 bilobed lobes); pars prostatica vesicular PSEUDOLECITHASTER B. Seminal vesicle tubular or moniliform ......... 3 3. A. Uterus mainly intercaecal; vitellarium 2 groups of 4 unbranched posteriorly oriented tubular lobes; seminal vesicle moniliform, antero-dorsal to ventral sucker . ASSITREMAB. Uterus reaches extracaecally; vitellarium a rosette arrangement of 7 short tubular distally branched lobes; seminal vesicle tubular, in forebody . . CLADOLECITHOTREMA TRIFOLIO VA RIUM Yamaguti , 1 940 [T(w) ] Body long and thin. Oral sucker funnel-shaped. Testes tandem to oblique; widely separated.Seminal vesicle elongate oval (or tubular and sinuous); in hindbody or dorsal to ventral sucker(or antero-dorsal to ventral sucker) ; connected to pars prostatica by short, aglandular duct. Parsprostatica tubular. Sinus-sac tubular. Laurer's canal present, uniting canalicular seminal recept-acle with dorsal surface. Vitellarium seven claviform lobes at level of ovary. 110 D. I. GIBSON & R. A. BRAY TYPE-SPECIES. Trifoliovarium acanthocepolae Yamaguti, 1940 [by original designation]. COMMENT. Yamaguti (1940) originally described the ovary as being three-lobed; hence thegeneric name, but later (1971) corrected this observation to four-lobed. Having examined thetype-material of T. acanthocepolae, we can confirm this emendation. The information given above in parentheses is taken from the descriptions of T. triacanthiBilqees, 1973, and T. triacanthusi Gupta & Ahmad, 1976. These species, which are probablysynonymous, were described from Triacanthus spp. off the Indian sub-continent. ASSITREMA Parukhin, 1976 Body small; oval to elongate oval. Gut-caeca wide. Testes symmetrical; separated by coils ofuterus. Seminal vesicle short, moniliform; winding antero-dorsally to ventral sucker. Parsprostatica tubular (but wider in middle according to figure). Sinus-sac small; oval. Laurer'scanal (?). Seminal receptacle (? blind or canalicular) present. Uterus almost entirely pre-ovarian;mainly inter-caecal. Eggs small. Vitellarium two symmetrical groups of four postero-laterallyoriented, digitiform lobes; centre of each group immediately post-ovarian. Excretory arms(?). TYPE-SPECIES. Assitrema eichleri Parukhin, 1976 [by original designation]. COMMENT. Parukhin's (1976c) figure indicates that the hermaphroditic duct is a continuation ofthe ejaculatory duct. In the other three genera of this subfamily the hermaphroditic duct is acontinuation of the metraterm. This may be just a matter of interpretation, for there is no evidencethat Parukhin sectioned either of his two specimens. There is a possibility, if the two specimensof Assitrema were young, that some of the differences between this genus and Cladolecithotremaare the result of age. This question cannot be resolved until further material of Assitrema isstudied. CLADOLECITHOTREMA Ichihara, 1970 [T(w,s)] Body elongate oval. Gut-caeca wide. Testes oblique; widely separated. Seminal vesicle tubular;convoluted in forebody. Pars prostatica tubular. Sinus-sac small; oval. Laurer's canal absent.Blind seminal receptacle present. Uterine field reaches extra-caecally. Vitellarium a rosettearrangement of seven digitiform, distally branched lobes; centre immediately post-ovarian. TYPE-SPECIES. Cladolecithotrema callionymi Ichihara, 1970 [by original designation]. COMMENT. We do not agree with Gupta & Sharma's (1975) proposed synonymy of Cladole-cithotrema and Trifoliovarium. We consider that the shape and position of the seminal vesicle,the shape of the Vitellarium and the absence or presence of Laurer's canal are sufficient criteriato distinguish these taxa. PSEUDOLEC1TH ASTER Campbell & Munroe, 1977 Body fusiform. Testes symmetrical; separated by coils of uterus. Seminal vesicle elongate oval;in forebody; connected to pars prostatica by short aglandular duct. Pars prostatica vesicular.Sinus-sac small; elongate oval. Ovary 'several irregular lobes' (four visible in figure). Laurer'scanal (?). Seminal receptacle (?). Vitellarium a rosette of twelve to sixteen lobes (figure suggestsca. seven bilobed lobes) ; at level of ovary. TYPE-SPECIES. Pseudolecithaster antimorae Campbell & Munroe, 1977 [by original designation]. Family PTYCHOGONIMIDAE Dollfus, 1937 Body medium sized; oval. Ecsoma absent. Body-surface smooth, without spines or plications.Oral and ventral suckers well developed; oral sucker larger than ventral sucker; latter situated inanterior half of body. Pharynx well developed. Oesophagus short. 'Driisenmagen' absent. Gut-caeca form uroproct. Testes two; post-ovarian; tandem; in middle of hindbody. Seminal vesicledilate, tubular; thin- walled; extending posteriorly into anterior hindbody. Pars prostatica THE HEMIUROIDEA 1 1 1 tubular. Ejaculatory and hermaphroditic duct short. Permanent sinus-organ a small cone.Sinus-sac absent. Genital atrium contains three distinct concentric folds in its wall which surroundsinus-organ. Genital pore mid-ventral in forebody. Ovary oval; pre-testicular in hindbody.Mehlis' gland pre-ovarian. Laurer's canal and uterine seminal receptacle present. Juel's organand canalicular or blind seminal receptacle absent. Uterine field extends between level posteriorto testes and ventral sucker. Eggs numerous; without filaments. Vitellarium follicular; occurs inlateral fields extending throughout most of hindbody. Excretory vesicle Y-shaped; arms unitetwice in forebody. Parasitic in stomach of elasmobranchs (normally carchariniform sharks). PTYCHOGONIMUS Liihe, 1900 [t(w,s)] Defined as family.TYPE-SPECIES. Ptychogonimus megastoma (Rudolphi, 1819) [by monotypy]. COMMENT. The above definition does not take into account the description of ' 'Ptychogonimusmegastoma' given by Vigueras (1956), which differs from other descriptions markedly andrequires confirmation. We have examined one type-specimen (whole-mount) of Ptychogonimus fontanus Lyster, 1939,and consider that, although it is not in good condition, this specimen appears to be an azygiid,bearing a strong resemblance to contracted forms of Azygia longa (Leidy, 1851). Family SCLERODISTOMIDAE Odhner, 1927 Prosogonotrematidae Vigueras, 1940 Bhaleraoiidae Srivastava, 1948 Mabiaramidae Teixeira de Freitas & Kohn, 1967 Body usually large; stout or elongate. Ecsoma absent. Body-surface smooth, but may be rugate.Oral and ventral suckers well developed ; ventral sucker just posterior to middle, in middle or inanterior half of body. Pharynx well developed. Oesophagus short. 'Driisenmagen' present orabsent. Gut-caeca terminate blindly close to posterior extremity. Testes two; symmetrical,oblique or in tandem; pre-ovarian; in forebody, dorsal to ventral sucker or in anterior hindbody.Seminal vesicle tubular; convoluted or winding in forebody. Pars prostatica tubular, occasionallywith wide lumen; long; convoluted or not; external gland-cells may be delimited. Ejaculatoryduct present; unites with metraterm within sinus-organ forming short hermaphroditic duct.Permanent sinus-organ usually well developed; conical to cylindrical. Sinus-sac well developed,weakly developed or apparently absent. Genital atrium well developed; often almost entirelyfilled by sinus-organ. Genital pore mid-ventral in forebody. Ovary globular to oval; well posteriorto and usually separated from testes by loops of uterus; in posterior forebody, dorsal to ventralsucker or anterior to mid-hindbody. Mehlis' gland usually posterior or postero-lateral, occa-sionally antero-lateral, to ovary. Laurer's canal present; opens dorsally or into rudimentaryJuel's organ. Rudimentary seminal receptacle present or absent. Canalicular or blind seminalreceptacle absent. Uterine seminal receptacle present. Uterus mainly in either fore- or hindbody;mainly pre- or post-ovarian. Eggs small; numerous; non-filamented. Vitellarium four to sevenconvoluted, tubular branches, which may subdivide; either mainly pre- or post-ovarian; eithermainly in fore- or hindbody. Excretory vesicle Y-shaped; stem relatively long; arms united inforebody. Manter's organ (accessory excretory vesicle) present; single or double; dorsal to stemof excretory vesicle. Parasitic in gut (mainly stomach) (?), occasionally in body-cavity, of marineteleosts. COMMENT. Parukhin (1976b) erected a new subfamily, the Pseudosclerodistomoidinae, within thisfamily for Pseudosclerodistomoides kurotchkini, a new genus and species from the gall-bladder ofLethrinus miniatus in the Indian Ocean. Several features of this species, such as the position ofthe testes and the genital pore and the nature of the seminal receptacle, suggest that it is not ahemiuroid. 112 D. I. GIBSON & R. A. BRAY Key to Sclerodistomidae 1. A. Manter's organ double; testes in anterior hindbody . . SCLERODISTOMINAE (p. 112)B. Manter's organ single; testes in forebody ......... 2 2. A. Ovary in forebody or at level of ventral sucker; uterus and vitellarium mainly pre-ovarian PROSOGONOTREMATINAE (p. 112)B. Ovary in hindbody; uterus and vitellarium mainly post-ovarian . PROSORCHIINAE (p. 112) Subfamily SCLERODISTOMINAE Odhner, 1927 Body stout. Ventral sucker near middle of body. 'Driisenmagen' present. Testes symmetrical tooblique; in anterior hindbody. Pars prostatica long and convoluted. Sinus-sac distinctly present;musculature diffuse; surrounding base of genital atrium. Sinus-organ a stout cone. Ovary nearor just anterior to middle of hindbody. Laurer's canal opens dorsally. Rudimentary seminalreceptacle present. Uterus almost entirely in hindbody; mainly posterior to gonads, reachingnear to posterior extremity. Vitellarium composed of convoluted, tightly helical, unbranched,filamentous tubules; commonly arranged with three on one side of body, four on other; presentlaterally in post-testicular region of hindbody. Manter's organ (accessory excretory vesicle)double; symmetrical. Parasitic in stomach and (?) body-cavity of marine teleosts. SCLEROD1STOMUM Looss, 1912 [t(w,s) ; n(w)] Mabiarama Teixeira de Freitas & Kohn, 1967Defined as subfamily.TYPE-SPECIES. Sclerodistomum italicum (Stossich, 1893) [by monotypy]. Subfamily PROSOGONOTREMATINAE Vigueras, 1940 Body stout. Ventral sucker in middle or just posterior to middle of body. 'Driisenmagen' absent.Testes symmetrical; in forebody. Pars prostatica long and sinuous or convoluted. Sinus-sac welldeveloped, but composed of diffuse musculature. Sinus-organ conical to cylindrical. Ovary inforebody or at level of ventral sucker. Laurer's canal short; opens into large rudimentary Juel'sorgan; dilated proximally forming small rudimentary seminal receptacle. Rudimentary Juel'sorgan post-ovarian [distinct in sections] . Uterus mainly pre-ovarian ; does not extend into hind-body. Vitellarium about three (two to four) convoluted, tubular branches on each side of body,which may subsequently divide; mainly pre-ovarian in forebody. Manter's organ (accessoryexcretory vesicle) single; median. Parasitic mainly in stomach of marine teleosts. PROSOGONOTREMA Vigueras, 1940 [t(w,s)] (?) Bhaleraoia Srivastava, 1948Defined as subfamily.TYPE-SPECIES. Prosogonotrema bilabiatum Vigueras, 1940 [by monotypy]. COMMENT. Nasir (1973) considers this genus to be monotypic, synonymizing seven other specieswith P. bilabiatum. We have included Bhaleraoia Srivastava, 1948, as a questionable synonym ofthis genus, because, although similar in gross morphology, it is poorly described and purportedto possess a uroproct. Subfamily PROSORCHIINAE Yamaguti, 1934 Body elongate oval to elongate. Ventral sucker normally within anterior half of body, butoccasionally in middle. 'Driisenmagen' absent. Testes tandem to almost symmetrical; in forebodyor dorsal to ventral sucker. Pars prostatica broad; usually straight or arcuate; lumen wide; THE HEMIUROIDEA 113 external gland-cells delimited. Sinus-sac apparently absent or (?) weakly developed. Sinus-organconical to cylindrical. Ovary in hindbody. Laurer's canal long and opening into rudimentaryJuel's organ or short and opening to exterior on dorsal surface; may or may not be dilate proxi-mally forming rudimentary seminal receptacle. Uterus mainly post-ovarian in hindbody.Vitellarium two to four branching or seven convoluted and filamentous tubules; mainly post-ovarian in hindbody; reaching near to posterior extremity. Manter's organ (accessory excretoryvesicle) single; median. Key to Prosorchiinae 1. A. Laurer's canal long, opening into rudimentary Juel's organ, dilated proximally forming rudimentary seminal receptacle PROSORCHIS B. Laurer's canal short, opening' dorsally to exterior; rudimentary seminal receptacle absent PROSORCHIOPSIS COMMENT. These two closely related genera essentially appear to differ only in the nature ofLaurer's canal. As few authors appear to have sectioned their material, many of the descriptionsin the literature must be used with some degree of caution. Nevertheless, both from the literatureand from our own sectioned material of Prosorchiopsis, it is evident that two distinct forms ofLaurer's canal appear to be present. PROSORCHIS Yamaguti, 1934 Laurer's canal long; opens distally into well-developed rudimentary Juel's organ ('terminalvesicle'); dilate proximally forming rudimentary seminal receptacle. TYPE-SPECIES. Prosorchis psenopsis Yamaguti, 1934 [by original designation]. COMMENT. The presence of a 'terminal vesicle' at the distal extremity of Laurer's canal has beenreported in a number of descriptions of species from this genus. Considering the nature of thesedescriptions, especially that of Yamaguti (1934), and the structure of the related Prosogonotrema,we have interpreted this 'terminal vesicle' as being a rudimentary Juel's organ. PROSORCHIOPSIS Dollfus, 1947 [t(w,s)] Laurer's canal short; opening dorsally to exterior; distal region may be slightly dilate andpossess glandular wall; rudimentary seminal receptacle absent. TYPE-SPECIES. Prosorchiopsis legendrei Dollfus, 1947 [by original designation]. COMMENT. In sectioned material, part of the distal region of Laurer's canal was slightly dilate andpossessed a diffuse, glandular wall (see Gibson & Bray, 1977). It is possible that this representsan early stage in the development of a rudimentary Juel's organ. It should be pointed out that a uterine seminal receptacle was not present in our sectionedmaterial, and its presence or absence could not be ascertained either from the literature or fromwhole-mounts. Considering that there is no alternative seminal storage apparatus and that it ispresent in Prosorchis, we can only assume that it is normally present in Prosorchiopsis. Addendum to Sclerodistomidae It is possible that Eurycoelum Brock, 1886, and Distoma gigas Nardo, 1827, two forms notrecorded since the nineteenth century, are also sclerodistomids; but the descriptions of thesetaxa are incomplete. Eurycoelum sluiteri was described (Brock, 1886) from the stomach ofLutjanus sanguineus [= Diacope metallicus] off Java. The genus has been considered by certainworkers, including Yamaguti (1971), to be a synonym of Hemiurus; but this is not the case. Infact it is possible that this genus may be a synonym of Prosogonotrema, which has been recordedfrom Lutjanus spp. on several occasions; but only an examination of the type-specimens, which 114 D. I. GIBSON & R. A. BRAY we have been unable to trace, or material from the type-host and locality can substantiate this.The situation with regard to Distoma gigas, a gigantic species from the stomach of Luvarusimperialis, has been discussed in detail by Gibson & Bray (1977). SCLERODISTOMOIDIDAE fam. nov. Body large; stout, elongate oval and attenuated anteriorly. Ecsoma absent. Body-surface smooth.Oral and ventral suckers well developed, small ; ventral sucker well inside anterior half of body.Prepharynx absent. Pharynx well developed. Oesophagus short. 'Driisenmagen' present. Gut-caeca sinuous; end blindly near posterior extremity, very close to stem of excretory vesicle (nounion observed). Testes two; slightly lobate; symmetrical to oblique; in hindbody close to ventralsucker; pre-ovarian. Seminal vesicle tubular convoluted in forebody. Pars prostatica short;tubular with wide lumen. Ejaculatory duct short. Hermaphroditic duct short; present withinsmall, cone-shaped permanent sinus-organ. Sinus-sac small and poorly developed or apparentlyabsent. Genital atrium well developed. Genital pore mid-ventral at level of pharynx. Ovary oval;in middle of body; separated from testes by loops of uterus. Mehlis' gland postero-lateral toovary. Laurer's canal and uterine seminal receptacle present. Canalicular or blind seminalreceptacle and Juel's organ absent. Uterus inter-caecal; coiled almost entirely in hindbody, inboth pre- and post-ovarian fields; with narrow, convoluted descending loop reaching near toposterior extremity and convoluted ascending loop which is initially narrow and then muchbroader. Eggs small; numerous; without filaments. Vitellarium tubular; with two main collectingducts situated medially, one anteriorly and other posteriorly oriented ; laterally directed dendriticbranches present between testes and level a short distance anterior to posterior extremity. Excre-tory vesicle Y-shaped; stem short; arms initially in dorsal and ventral fields, pass laterally andunite in forebody. Parasitic in gall-bladder of marine teleosts. COMMENT. We have erected a new family for the genus Sclerodistomoides Kamegai, 1971, becauseit differs significantly from the accacoeliids in the structure of the pharynx, from the sclerodisto-mids in the absence of Manter's organ, and from both groups in the unique orientation of themain collecting ducts of the vitelline system. Its closest relative appears to be the accacoeliidgenus Paraccacladium. SCLERODISTOMOIDES Kamegai, 1971 [T(w) ; t(s)] Defined as family.TYPE-SPECIES. Sclerodistomoides pacificus Kamegai, 1971 [by original designation]. COMMENT. Lintonius novikovi Baeva, 1965, does bear some superficial resemblance to Sclero-distomoides, but the description of this species by Baeva (1965) does not include enough data toconfirm this. Yamaguti (1971) suggested that it might be a sclerodistomid. Family SYNCOELIIDAE Looss, 1899 Body elongate or dorso-ventrally flattened; usually with pedunculate ventral sucker. Ecsomaabsent. Body-surface smooth, but commonly papillate on forebody and on peduncle, if present.Oral and ventral suckers well developed; may possess accessory suckers around their rim.Glandular cells common in subtegumentary parenchyma and within musculature of suckers.Pharynx well developed. Oesophagus short. Cyclocoel usually present, but gut-caeca may endblindly ( ?) or form a uroproct. Testes eleven to eighteen distinct, oval follicles (usually arrangedin pairs), seven to eight transverse rows of small follicles, or just a large number of irregularfollicles; pre-ovarian, in hindbody. Seminal vesicle thin-walled; tubular; winding or sinuous; inforebody. Pars prostatica tubular. Ejaculatory duct short. Hermaphroditic duct and genitalatrium present, but indistinguishable when sinus-organ is absent. Permanent sinus-organ andsinus-sac present or absent. Genital pore mid-ventral in anterior forebody. Ovary post-testicular;composed of five large, oval, isolated lobes or numerous irregular follicles. Laurer's canal and THE HEMIUROIDEA 115 uterine seminal receptacle present. Juel's organ and canalicular or blind seminal receptacleabsent, but rudimentary seminal receptacle may be present. Uterus passes posteriorly but coilsmainly in pre-ovarian hindbody. Eggs numerous, small, non-filamented. Vitellarium usuallyseven (occasionally five or six) isolated, oval lobes, or irregular acinous bunches or rows offollicles; post-ovarian. Excretory vesicle Y-shaped; arms united in forebody, may initially runin dorsal and ventral fields. Free floating metacercarial stage present. Parasitic in branchial andbuccal cavities, on skin, in (?) oviduct and in (?) gut of elasmobranchs and marine teleosts. Key to Syncoeliidae 1. A. Ovary numerous irregular follicles arranged in rows; vitellarium irregular acinous bunches or rows of follicles OTIOTREMATINAE (p. 115) B. Ovary 5 large isolated lobes; vitellarium 5 to 7 oval, isolated lobes . SYNCOELIINAE (p. 116) Subfamily SYNCOELIINAE Looss, 1899 Small accessory suckers around rim of suckers absent. Peduncle usually present. Cyclocoelpresent. Testes eleven to eighteen distinct, oval lobes; usually arranged in pairs. Permanentsinus-organ present or absent. Hermaphroditic duct and genital atrium present, but indistinguish-able when sinus-organ is absent. Sinus-sac absent or rudimentary. Ovary composed of five large,isolated follicles. Rudimentary seminal receptacle may be present as proximal dilation of Laurer'scanal. Uterus arranged in large, regular loops dorsally and ventrally to gonads. Vitellariumseven (occasionally five or six) small, isolated, oval lobes. Parasitic in branchial and buccalcavities (? with occasional records from gut) of sharks and marine teleosts. COMMENT. Our work with this group indicates that Syncoelium Looss, 1899, can be convenientlysplit into two distinct genera on the basis of the presence or absence of a sinus-organ (Gibson &Bray, 1977). When present, the sinus-organ is a well-developed structure, visible in sections andwhole-mounts in both adults and metacercariae (see Gibson, 1976). In addition, in forms lackinga sinus-organ the genital atrium appears to be indistinguishable from the hermaphroditic duct,the hindbody tends to be spatulate rather than tubular, and the ventral sucker is somewhat lesspedunculate. Furthermore, the latter forms have been recorded from the gills, whereas the formspossessing a sinus-organ usually occur in the buccal cavity and on the gill-arches. Key to Syncoeliinae 1 . A. Permanent sinus-organ absent ; hermaphroditic duct indistinguishable from genital atrium ;tendency for hindbody to be spatulate; ventral sucker normally sessile or on short peduncle; normally parasitic on gills SYNCOELIUM B. Permanent sinus-organ present; hermaphroditic duct easily distinguishable from genitalatrium; hindbody usually tubular; ventral sucker usually on well-developed peduncle;usually parasitic in buccal cavity or on gill-arches COPIATESTES SYNCOELIUM Looss, 1899 Hindbody broad or spatulate. Ventral sucker sessile or surmounted on short peduncle. Permanentsinus-organ absent. Hermaphroditic duct indistinguishable from genital atrium. Parasitic ongills (? and in intestine) of sharks and marine teleosts. TYPE-SPECIES. Syncoelium ragazzii (Setti, 1897) [by monotypy]. COPIATESTES* Crowcroft, 1948 [n(w,s)] Hindbody elongate, tubular. Ventral sucker surmounted on well-developed peduncle. Permanentsinus-organ present. Hermaphroditic duct and genital atrium easily distinguishable. Parasitic in * It is also spelt Capiatestes in original publication, but this is a typographical error. 116 D. I. GIBSON & R. A. BRAY branchial (especially gill-arches and gill-rakers) and buccal cavities (?and intestine) of marineteleosts. TYPE-SPECIES. Copiatestes thyrsitae Crowcroft, 1948 [by original designation]. Subfamily OTIOTREMATINAE Skrjabin & Guschanskaja, 1957Paronatrematinae Skrjabin & Guschanskaja, 1957 [proposed, but not named, by Dollfus (1950)]. [Paronatrema is poorly known.] Accessory suckers may be present around rim of suckers.Cyclocoel present (?or absent; caeca may end blindly or form uroproct). Testes numerousirregular follicles or seven to eight irregular transverse rows of follicles. Hermaphroditic ductpresent within sinus-sac (? not clearly described in Paronatrema). Permanent sinus-organ absent.Ovary composed of numerous irregular follicles which may be arranged in rows. Vitellariumirregular acinous bunches or rows of follicles. Parasitic in branchial cavity or on skin (? or inoviduct or intestine) of sharks and rays. Key to Otiotrematinae 1. A. Small accessory suckers present on oral sucker and/or ventral sucker . PARONATREMAB. Small accessory suckers on suckers absent (papillae present within oral sucker) OTIOTREMA OTIOTREMA Setti, 1897 [t(w,s)] Forebody cylindrical; hindbody flattened, alate, recurved. Papillae present within oral sucker;small accessory suckers within suckers absent; ventral sucker pedunculate. Gut-caeca sinuous inforebody; with numerous diverticulate outgrowths in hindbody; forming cyclocoel. Sinus-saclarge, reaching close to dorsal surface. Ovary and vitellarium consisting of numerous acinousbunches of follicles, posterior to numerous follicular testes. Uterus in transverse coils; present inlateral fields of hindbody. Parasitic in branchial cavity ( ? or intestine) of sharks. TYPE-SPECIES. Otiotrema torosum Setti, 1897 [by original designation]. COMMENT. We have examined some of the material collected by Looss, and it appears to agreewell with his description (Looss, 1899). PARONATREMA Dollfus, 1937 [t(w); n(w)] [This genus is poorly known.] Forebody sub-cylindrical; hindbody flattened, oval. Small accessorysuckers present within oral and/or ventral suckers; ventral sucker large, but apparently notpedunculate. Gut-caeca sinuous; apparently end blindly (? or form uroproct or cyclocoel: inter-pretations uncertain). Testes consist of rows of follicles or segmented tubules. Ovary composedof irregular follicles (interpretations conflict). Vitellarium consists of rows of follicles or seg-mented tubules. Uterus numerous transverse coils in hindbody. Parasitic on skin or (?) in oviductor stomach of sharks and rays. TYPE-SPECIES. Paronatrema vaginicola Dollfus, 1937 [by monotypy]. COMMENT. It would appear that in some descriptions the ovary and Mehlis' gland may have beenconfused. Generic Index to part Ml Acanthuritrema 106 Accacoelium . ... 58 Accacladium 58 Acerointestinecola 88 Accacladocoelium 58 Adinosoma 97 THE HEMIUROIDEA 117 Aerobiotrema Ahemiurus Albulatrema . Allogomtiotrema Allostomachicola Allotangiopsis Anahemiurus . Anguillotrema Aphanhystera Aphanuroides Aphanurus Apoblema Aponurus Arnold . Arnoldia Assitrema Atheria Azygia . Bathycotyle . Bhaleraoia Bilacinia Botulus Brachadena . Brachyphallus Bunocotyle Caballeriana . Capiutestes . Catarinatrema Ceratotrema . Chauhanurus . Chelatrema . Chenia . Cladolecithotrema . Clupenurus . Copiatestes . Cyatholecithochirium Cylindrorchis Derogenes Derogenoides Deropegus Dichadena Dictysarca Dinosoma Dinurus Dissosaccus . Distoma gigas Dollfuschella . Dollfustra vassosius Duosphincter . Ectenurus Elongopar orchis Elytrophalloides Elytrophallus . Erilepturus Eurostomum . Eurycoelum . Follicovitellosum Genarchella . Genarches 82 Genarchopsis .65 Genolinea 83 Glomericirrus61 Gomtiotrema87 Gonocerca 77 Gonocercella . 85 Grassitrema . 77 Guschanskiana61 Halipegus 65 Hassallius 65 Helaphanurus . 85 Hemipera102 Hemiperina . 78 Hemiurus78 Hirudinella 110 Hirudinelloides 87 Holacanthitrema 61 Hydrophitrema 62 Hypohepaticola 112 Hysterolecitha 108 Hysterolecithoides . 99 Indoderogenes 1 02 Indostomachicola 94 Intuscirrus 64 Isoparorchis .58 Jajonetta 115 Johniophyllum 94 Josstaffordia . 92 Lampritrema . 65 Laticaudatrema 81 Lecithaster 78 Lecithochirium 110 Lecithocladium 89 Lecithophyllum115 Lecithurus 94 Leptolecithum 83 Leptosoma 72 Lethadena 73 Leuceruthrus .78 Leurodera 106 Lintonius 82 Liocerca97 Liopyge. 86 Lobatovitellovarium94 Mabiarama . 113 Macradena .76 Macradenina . 83 Magnacetabulum 66 Magnibursatus 87 Magniscyphus83 Me coder us 90 Mediolecithus89 Megadistomum87 Merlucciotrema61 Metahemiurus 113 Mimodistomum 108 Mitrostoma . 76 Mneiodhneria . 74 Monolecithotrema . 78 67 90 61 75 73 95 58 76 61 65 75 75 85 99 100 108 98 91 105 105 70 88 67 101 92 90 61 100 98 102 92 90 103 88 101 102 95 62 73 114 72 72 108 112 107 106 87 79 93 88 99 61 96 85 61 67 58 70 118 D. I. GIBSON & R. A. BRAY Monorchiaponurus . Monorchimacradena Monovitella . Mordvilkoviaster Musculovesicula Myosaccium . Neodichadena Neogenolinea Neohemiurus . Neohysterolecitha . Neotheletrum Odhnerium Ophiocorchis . Opisthadena . Orophocotyle Orthoruberus Otiotrema Otodistomum Paraccacladium Paradinurus . Parahalipegus Parahemiurus Paraplerurus . Parasterrhurus Paratetrochetus Paravitellotrema Parectenurus . Paronatrema . Pelorohelmins Plerurus Plicatrium Profundiella . Progenarchopsis Progonus Prolecitha Prolecithochirium . Pronopyge Prosogonotrema Prosorchiopsis Prosorchis 104 Prosterrhurus 107 Proterometra . 79 Pseudazygia . 1 02 Pseudobunocotyla . 90 Pseudodichadena 66 Pseudodinosoma 107 Pseudogenarchopsis 66 Pseudolecithaster 85 Pseudosclerodistomoides 93 Pseudostomachicola 68 Ptychogonimus 58 Pulmovermis .78 Qadriana 67 Quadrifoliovarium . 59 Rhynchopharynx 73 Saturnius 116 Sclerodistomoides . 61 Sclerodistomum 60 Separogermiductus .88 Sterrhurus 78 Stomachicola 85 Synaptobothrium 96 Syncoelium 67 Tangiopsis 59 Tetraster 76 Tetrochetus . 87 Theletrum 116 Thometrema . 83 Thulinia 96 Tricotyledonia 95 Trifoliovarium 99 Tubulovesicula 76 Tyrrhenia 74 Unilacinia108 Uroproctinella 95 Uterovesiculurus 85 Vitellotrema . 112 Voitrema 113 Xenodistomum113 88616167 1079578 110 11188 11198 104 1085964 114 11292928897 1158083596980 10595 1098880 1099987769761 IV. A discussion on the evolution of the Hemiuroidea Evolutionary trends in the Hemiuroidea The presentation of any evolutionary picture for the Platyhelminthes must remain hypothetical,as it is unlikely that there will ever be any fossil record due to the soft-bodied nature of theseanimals. Possible evolutionary patterns can only be exposed by the knitting together of generalmorphological trends in organs, organ-systems and whole animals. Having distinguished a trend,there is the problem of deciding which way the trend is moving, and hence which is the primitiveand which is the advanced condition. In addition, the possibility should not be forgotten that anintermediate form is primitive and that evolution is proceeding in two opposite directions. Inorder to assess which form is primitive, it is helpful to adopt the use of certain external indicators.As far as parasitic helminths are concerned useful indicators include: 1. The supposed 'primitiveness* of the host Although superficially it appears more likely that the more archaic and primitive vertebratesharbour more archaic and primitive parasites, this is not necessarily so. Owing to the variable THE HEMIUROIDEA 119 ecological factors involved, archaic hosts can harbour what appear to be 'advanced' parasites,and vice versa. In addition, there are often widely differing opinions as to the relative agesof certain groups of vertebrates, and this tends to limit its value as an indicator. One mightexpect, however, that a group of helminths restricted to birds would be more advanced thanone restricted to elasmobranchs. Unfortunately, the vast majority of the hemiuroids areparasitic in fishes, and, although certain primitive groups are recognized, it is not knownfor certain whether elasmobranchs are more primitive than bony fishes (Osteichthyes). Amongst the hemiuroids only the azygiids appear to occur in fishes which are widely held to beprimitive. Otodistomum commonly occurs in the shark Hexanchus and has been recorded fromChlamydoselachus and Heterodontus, and both Azygia and Leuceruthrus occur in the holosteanAmia. Other groups occuring in elasmobranchs are the ptychogonimids and the syncoeliids, thePtychogonimidae and the Otiotrematinae being entirely restricted to these hosts. Azygia hasalso been recorded from Acipenser, a member of primitive group Chondrostei; but little emphasiscan be placed upon this result as Derogenes and several species of hemiurid have also beenrecorded from this host. This apparent mixture of what we believe to be 'primitive' and relatively'advanced' forms is possibly associated with the migratory habit of sturgeons and the low degreeof host-specificity exhibited by some of the more 'advanced' hemiuroids. There is also a singlerecord of Halipegus from the related chondrostean Polyodon. Except for certain halipeginederogenids, which occur in amphibians and, rarely, in amphibious snakes, and the pulmoverminehemiurids, which are restricted to the lungs of sea-snakes, the remainder of the hemiuroids occurin teleosts. 2. The habitat of the host Parasites of aquatic vertebrates will tend to be more primitive than those from terrestrialvertebrates, because aquatic vertebrates tend to be more primitive than terrestrial vertebratesand because it is much easier to envisage the origins of parasitic platyhelminths in aquaticconditions. All the hemiuroids are parasitic in aquatic or amphibious hosts, the majoritybeing parasitic in marine teleosts, but a few groups are commonly found in freshwater hosts.Unfortunately, there is no conclusive evidence to suggest that teleosts arose in freshwater,or vice versa, although a freshwater origin is preferred by some workers. It should beemphasized that any evidence based upon the habitat of the host should be treated withcaution, as various hosts may have passed from fresh- to salt-water or from water to land,and back, on more than one occasion during the course of their evolution. Amongst the hemiuroids, only the azygiids and the halipegine derogenids are successful parasitesof freshwater fishes, and only the isoparorchiids, a very small group, are restricted to these hosts.One interesting coincidence is that all three of the azygiid genera from freshwater fishes occur inNorth America, two being endemic, and that this is the only region of the world where holosteanfishes survive. Another possible coincidence is that the majority of halipegine genera and themajority of isoparorchiid records occur in Asia, especially in the southern half of the continent:this location is the possible centre of evolution and radial dispersion of freshwater teleosts (seeDarlington, 1957). 3. Host-specificity One might expect helminths with a high-degree of host-specificity to be more primitive thanthose with a low-degree. This is because it is likely that highly specific associations developover a long period of time, and once they have arisen the further evolution of the parasiteitself tends to be restricted to within the limits of the evolution of the host. This is a verygeneral feature, however, and as digeneans tend to have a low degree of host-specificity withregard to their vertebrate host, it is of limited value. It is worth noting, nevertheless, that the host-range of the adult forms of certain groups andgenera do tend to be restricted. The accacoeliines, with the exception of Tetrochetus, occur onlyin molid teleosts and the ptychogonimids appear to be entirely or almost entirely restricted togaleomorph sharks. Bathycotyle and Hirudinella parasitize scombroid and coryphaenid teleosts, 120 D. I. GIBSON & R. A. BRAY and Botulus and Lampritrema are usually restricted to Alepisaurus and Lampris, respectively.Prominent among other examples are the macradeninine and quadrifoliovariine lecithasterids,which occur only in acanthurid teleosts. Alternatively, many members of the Hemiuridae,Lecithasteridae, Bunocotylidae and Derogenidae appear to exhibit little or no host specificityamongst marine teleosts, although certain individual species or genera may appear to be highlyhost-specific. One species of Halipegus is reported to occur in freshwater teleosts and amphibians.The azygiids are present in freshwater teleosts, elasmobranchs, holosteans and rarely in chondro-steans, and although they appear to be restricted to certain groups of elasmobranchs, they appearto exhibit little host-specificity. It is obvious in many of the above cases, e.g. the accacoeliines, that much of the apparenthost-specificity is ecological rather than immunological or physiological, and it is likely thatecologically based host-specificity has less evolutionary significance, as it would appear that anecological restriction is a prerequisite for the development of other types of host-specificity. Ourlack of knowledge of the life-history in many cases, however, prohibits the differentiation of thesetypes. Nevertheless, the above examples do tend to illustrate the fact that there is a tendency forthe successful groups, such as derogenids, hemiurids, lecithasterids and bunocotylids to exhibitin general a low degree of host-specificity, while the smaller groups, such as accacoeliids,hirudinellids, ptychogonimids, etc. tend to be more restricted. If our hypothesis that host-specificity is acquired over a long period of association is correct, then it is likely that these smallergroups will tend to be more primitive than the larger. The azygiids occupy an anomalous positionin that to some extent they are restricted to particular groups of fishes, but within these groupsthey are widespread. This might be explained by the fact that they are a small, but successful,group which occupy niches, i.e. the stomach of freshwater fishes and elasmobranchs, wherecompetition from other digeneans is severely limited. 4. Related groups Undoubtedly the most important evidence can be taken from features common in groupswhich are held to be related to, and perhaps more primitive than, the group under study.Digeneans, monogeneans, cestodes and aspidogastreans are generally thought to haveevolved from primitive rhabdocoel turbellarians, possibly similar to the Dalyellida, whichmay inhabit the mantle-cavity or viscera of bivalves. Most authorities now agree that theAspidogastrea is the closest relative of the Digenea, and Rohde (1971a) in an abstract states:'The Aspidogastrea are considered to be primitive, direct decendents of turbellarians, whichare not yet closely adapted to parasitism and have not yet incorporated the vertebrate hostas a fixed component in their life-cycle. They are closely related to the ancestors of theDigenea. Aspidogastrea and Digenea are both primarily parasites of molluscs.' In the samecontext Rohde (1971b) refers to the Aspidogastrea as 'living fossils'. It is likely, therefore,that features common to the Aspidogastrea and Digenea either must be primitive or arefeatures produced by parallel or convergent evolution. Some primitive features may also becommon in other parasitic platyhelminths and in the rhabdocoels; but, since these groupsare successful, widely specialized and more distantly related, great care should be taken inthe interpretation of any correlations, as the same features have undoubtedly been evolvedindependently by parallel and convergent evolution. Beklemishev (1964 [1969]), for example,states, when discussing the reproductive system of the Platyhelminthes : 'In spite of the greatdiversity of these adaptations, which appear independently in the various groups, the prob-lems involved are repeatedly solved by similar methods, and that in animals far apart in thesystem.' When attempting to decide which of a group is primitive, one must, therefore, look for a succes-sion of trends which tend to flow in the same direction. It is unlikely, however, that one willencounter all of the trends proceeding 'satisfactorily' in the same animal. It is a fact that paralleland convergent evolution do occur, and each species is adapted to its particular niche rather thanto illustrate an evolutionary picture. Parallel evolution is important because, as the members ofthe group originally shared the same gene-pool, the same mutations are likely to occur down theseparate evolutionary branches, and thus the same features may evolve independently in several THE HEMIUROIDEA 121 different sub-groups. It is essential, therefore, that one looks at the overall trends in the group asa whole. This is especially important where the loss of organs may have occurred. In an attempt to show the evolutionary trends within the Hemiuroidea, we have followedthree different organs and organ-systems in which definite trends do occur. These are: (1) theseminal storage and disposal apparatus in the female reproductive system; (2) the vitellarium;and (3) the terminal genitalia. (1) Seminal storage and disposal apparatus in the female reproductive system. One of the mostsignificant, but not one of the most obvious, trends in the Hemiuroidea is the development ofthe seminal storage and disposal apparatus, especially the latter, in the female system. In themajority of hemiuroids the proximal region of the uterus forms a seminal reservoir and is termedthe uterine seminal receptacle. As a uterine seminal receptacle occurs in the Aspidogastrea (seeRohde, 197 la), it is likely that this condition is primitive in digeneans. Evidence from otherplatyhelminth-groups is difficult to interpret as they are specialized and involve, in the case ofthe Turbellaria, a vagina (copulatory canal) and several different types of seminal receptacle, and,in the case of the Monogenea and Cestoda, usually a vagina (or vaginae) with a dilation whichforms a seminal receptacle. However, in some rhabdocoel turbellarians such as Mesostoma, aseminal receptacle in the form of a dilation of the oviduct does occur. Considering that the ovo-vitelline canal, which is the equivalent of the uterus in the Digenea, is short and that there is noMehlis' gland, this feature is somewhat similar to a uterine seminal receptacle. As stated above, the sperm in the majority of hemiuroids is stored in the proximal region ofthe uterus. From the uterus small amounts of activated sperm pass through Mehlis' gland,where presumably fertilization of the ova usually occurs. Excess and spent sperm, plus excessvitelline material, are then disposed of via Laurer's canal, which in certain groups, e.g. theAzygiidae, Accacoeliidae and Hirudinellidae, connects the oviduct with the exterior via a dorsalpore (see Fig. 6; arrangement A). Such sperm and vitelline material in Laurer's canal can beseen in sectioned material: occasionally ova are also present. This process is naturally verywasteful, and it is apparent that certain turbellarians and monogeneans have developed ananalogous duct, the genito-intestinal canal, which disposes of similar residues by transportingthem into the gut, in order that this material can be re-processed. Our work has shown that somehemiuroids appear to have evolved a special organ, Juel's organ, within which this waste-materialis degraded and re-absorbed. It is clear that this organ did not arise overnight, as traces of itsdevelopment can be seen in present forms. In groups, such as Gonocercinae, Syncoeliinae andIsoparorchiidae, the proximal region of Laurer's canal is slightly dilated, forming a rudimentaryseminal receptacle, within which excess spermatozoa and vitelline material are stored beforepassing along the remainder of the canal (see Fig. 6; arrangement B). Our observations suggestthat the excess material is killed or stored until it dies, and that it may begin to disintegrate withinthe rudimentary seminal receptacle, before being passed along the canal. The distal part of thecanal in these groups tends to be slightly glandular in nature, and the pore itself is often tightlyclosed by a sphincter: thus, it is possible that some re-absorption may occur in these distalregions. In forms such as Derogenes and apparently Prosorchis, a rudimentary Juel's organ isfound (see Fig. 6; arrangement C). In these cases the Laurer's canal does not open to the exterior,as the distal part of the duct is modified and forms an oval structure with a similar amorphousappearance to that of a fully-developed Juel's organ. During the course of evolution, Laurer'scanal has become shorter, thus bringing the rudimentary Juel's organ and rudimentary seminalreceptacle closer together. In Prosogonotrema these two structures are very close together(Fig. 4B). This process has continued until the rudimentary Juel's organ completely envelopesthe rudimentary seminal receptacle, thus forming a complete Juel's organ (see Fig. 6; arrangementD). The enclosed rudimentary seminal receptacle has been known in the past as the 'inner vesicle'(Juel, 1889; Lander, 1904). A complete Juel's organ has been observed in Genarchopsis(Anjaneyulu, 1968; Madhavi & Rao, 1974), Elongoparorchis (Madhavi & Rao, 1974), innumerous hemiurids, knowingly or unknowingly, by several authors, including Juel (1889) andLander (1904), and by ourselves in various hemiurids, Hysterolecitha and Arnola. A final deve-lopment, which appears to have occurred during the development of the Opisthadeninae, and usr B Fig. 6 Different arrangements of the seminal storage and disposal apparatus in the femalereproductive system (see text), [bsr, blind seminal receptacle; Jo, Juel's organ; Lc, Laurer's canal;rJo, rudimentary Juel's organ; rsr, rudimentary seminal receptacle; usr, uterine seminal receptacle.] THE HEMIUROIDEA 123 probably the majority of the lecithasterids, is that the inner vesicle expands to fill Juel's organ,thus forming a blind seminal receptacle (see Fig. 6; arrangement E). The uterine seminal receptacleis lost in these groups. A blind seminal receptacle tends to be a large, thick-walled structure,which is connected to the oviduct by a narrow duct: the sole remnant of the original Laurer'scanal. This final development presumably means that the spermatozoa pass through Mehlis'gland in the opposite direction to that which normally occurs in the remainder of the hemiuroids.Spent spermatozoa and excess vitelline material are, therefore, voided via, or broken down andre-absorbed by, the uterus. The evidence, which suggests that the presence of Laurer's canal opening to the exterior inconjunction with a uterine seminal receptacle is primitive, is that this is exactly the same~arrange-ment which occurs in the majority of aspidogastreans (e.g. Multicotyle, Lophotaspis, Cotylo-gasteroides, Macraspis}. The development of a seminal and vitelline disposal organ, however,is not limited to the Juel's organ of some hemiuroids. It appears that analogous structures mayhave developed in an aspidogastrean and certain turbellarians. Stafford (1896) described Laurer'scanal of Aspidogaster conchicola Baer, 1826, as ending blindly in the form of a 'thick-walled bulb',and Voeltzkow (1888) refers to the same structure as a 'receptaculum vitelli' because it appearedto contain vitelline residues.* The absorption of excess sperm by the Turbellaria is discussed byde Beauchamp (1961, p. 31). He notes that, in addition to the genito-intestinal canal whichoccurs in some groups, there appear to be several different organs involved: these include the'vesicle of Lang' of the polyclads (see Bock, 1927), the 'vesicula resorbiens' of the Kalyptorhynchia,and the copulatory bursa, which is found in many turbellarians. It is clear that, while there isa need to dispose of excess and spent seminal and vitelline material, there is in free-livinghelminths a strong selective pressure for the development of an organ of re-absorption, whichthus aids the animal's economy. Owing to the ready availability of food, this pressure is probablymuch less in the parasitic forms, as demonstrated by the number of digeneans which still useLaurer's canal as a seminal and vitelline drain, but it would still appear to be advantageous to theeconomy of the parasite for it to develop a less wasteful system. If the actual biology of thesedigeneans is examined in detail, it is clear that many hemiuroids are stomach-parasites, and thatthey have developed mechanisms which protect them from the low pH and, in the case of marineteleosts, the high osmolarity of the environment (MacKenzie & Gibson, 1970; Gibson, 1971).The hemiurids which live in such conditions apparently withdraw their ecsoma and contract,with the result that they are protected by their thick tegument, and the derogenids from thestomach tend to migrate anteriorly towards the oesophagus during periods of low pH or highosmolarity. These parasites, therefore, contrary to intestinal forms, do not appear to be in aposition to feed at all times. It would seem, consequently, that it is advantageous for theseparasites to re-utilize some of its waste-material in order to help maintain egg-production duringperiods when feeding is limited. The presence of a structure resembling a rudimentary Juel's organ in Aspidogaster conchicoladoes suggest that Juel's organ may also be a primitive feature; but this structure appears not tohave been observed in other aspidogastreans. In addition, it appears that a similar structure maybe present in digeneans unrelated to the hemiuroids, e.g. Styphlodora bascaniensis Goldberger,1911 (see Goldberger, 19116), and Cyclocoelum sharadi Bhalerao, 1935 (see Madhavi & Rao,1974), and that this feature has not apparently been reported in other species of these generawhica have been examined. It would seem, therefore, that a distal modification of Laurer's canal,which appears to be associated with the degradation of seminal and vitelline material, has beenindependently evolved on at least four different occasions. This would appear to vindicateBeklemishev's statement quoted above. Only in the hemiuroids, however, does this organ appearto have developed further, i.e. past the 'rudimentary' stage, and only in the hemiuroids is itcommon to entire groups. In other instances, it appears to have been developed independently by * Voeltzkow claimed to have seen the canal open to the exterior in young animals, and that the 'receptacle' developedas the animal matured. Stafford, however, was of the opinion that Laurer's canal developed as an outgrowth fromthe oviduct. 124 D. I. GIBSON & R. A. BRAY species, possibly recently, to meet their present ecological requirements. This is supported by thefact that none of the latter species are gut-parasites, and, therefore, such a development wouldprobably be economically advantageous. Many digeneans have lost Laurer's canal, or have altered its function, i.e. in some groups it isused as a vagina. The latter occurrence we consider to be an advanced feature (Gibson & Bray,1975), and species which use this method of copulation (one sided, as opposed to the possibilityof reciprocal copulation where the genital atrium is used) normally have a thin-walled canalicularseminal receptacle, formed as a proximal dilation of Laurer's canal, and no uterine seminalreceptacle, e.g. Diphterostomum bmsinae (Stossich, 1889) and Haploporus benedeni (Stossich,1887) - see Palombi (1931). We should emphasize that remarkably few digeneans have ever beenseen in the act of copulation. Assuming, from the above evidence, that the presence of Laurer's canal opening dorsally anda uterine seminal receptacle are, in the Hemiuroidea, primitive characters, it is not unreasonableto presume that Juel's organ has evolved in the manner described above. The derivation of theblind seminal receptacle of the opisthadenines and the majority of the lecithasterids from Juel'sorgan is not so obvious. If one discounts the possibility that it arose independently as a diverti-culum of the oviduct, there appears to be only one other alternative. That is, its independentderivation from the rudimentary seminal receptacle. In the Lecithasteridae, Trifoliovarium has alarge, functional canalicular seminal receptacle which has presumably evolved directly from arudimentary seminal receptacle. The blind seminal receptacle of the related Cladolecithotremahas presumably evolved by the loss of Laurer's canal. Alternatively, in Hysterolecitha andpresumably Hysterolecithoides Juel's organ is present. The blind seminal receptacle of the re-mainder of the lecithasterids could, therefore, have evolved from either a rudimentary seminalreceptacle or Juel's organ. As the inner vesicle of Juel's organ appears to have been derived fromthe rudimentary seminal receptacle, this is essentially the same thing; but the thick, fibrous wallof the blind seminal receptacle is quite different to the relatively thin-walled type of seminalreceptacle which usually occurs in digeneans. This suggests that the wall of the blind seminalreceptacle may be derived from the outer capsule of Juel's organ. There is also evidence that theblind seminal receptacle of the opisthadenines has evolved from Juel's organ of the hemiuridsand, as discussed below, that a similar blind seminal receptacle appears to have arisen inde-pendently from Juel's organ in the Didymozooidea. Although the form of the seminal storage and disposal system tends to be relatively constantwithin a family or subfamily, there is a notable exception to this. In the Derogenidae a variety ofconditions occur: (1) many halipegines, such as Halipegus, possess Laurer's canal, which opensdorsally, and a uterine seminal receptacle; (2) other forms, such as the Gonocercinae, afe similarexcept that a small, but distinct, rudimentary seminal receptacle occurs; (3) in the remainder ofthe halipegines, such as Genarchopsis [but see p. 79] and Arnola, a fully developed Juel's organis present ; and (4) in the derogenines a continuous variation of conditions occur : (a) Derogenespossesses a large rudimentary seminal receptacle containing spermatozoa which is connected byLaurer's canal to a rudimentary Juel's organ ; (b) in Progonus the rudimentary seminal receptacleis further enlarged to function as the only seminal store, the uterine seminal receptacle being lost,and the rudimentary Juel's organ is present at the junction of the seminal receptacle and Laurer'scanal, which ends blindly; and (c) in Leurodera Laurer's canal and the rudimentary seminalreceptacle appear to have been lost, leaving a blind seminal receptacle. The variation whichoccurs in this group can perhaps be explained by the fact that it is a large, successful group,possibly with primitive origins, arising at about the time when the first variations of the primitiveseminal storage and disposal apparatus, such as the development of Juel's organ, were beginningto occur. It is possible that parallel evolution is responsible for some of the conditions whichoccur in this group and their apparent similarity to the arrangements in other hemiuroid groups. (2) Vitellarium. There appears to be a very clear trend in the form of the vitellarium in theHemiuroidea. Briefly, commencing with a follicular form, and passing through tubular and seven-lobed stages, the vitellarium is finally reduced to two, or occasionally one, oval masses. The trendbegins with the follicular vitellarium which occurs in the Azygiidae (Fig. 7; arrangement A). THE HEMIUROIDEA 125 B Fig. 7 Different arrangements of the vitellarium (see text). 126 D. I. GIBSON & R. A. BRAY These follicles become linked together along the collecting ducts, thus giving a chain-like appear-ance, as occurs in the syncoeliid Otiotrema and to some extent in the accacoeliid Tetrochetus(Fig. 7; arrangement B). The vitellarium then becomes distinctly tubular, consisting of manylong, often convoluted, tubules, which may be branched (Fig. 7 ; arrangement C). The latter typeof vitellarium occurs in the Accacoeliidae, Hirudinellidae and Isoparorchiidae. The next stageis that the number of tubules, which are usually unbranched, is reduced to seven: these usuallybeing arranged with three on one side of the body and four on the other (Fig. 7 ; arrangement D) ;e.g. some sclerodistomids and some hemiurids, such as Dinurus and Stomachicola. The length ofthe seven tubules is then gradually reduced, so that they pass through digitiform (e.g. Lecitho-cladium, Plerurus, Ectenurus), tear-shaped (e.g. Elytrophallus, Lecithaster, Hysterolecitha) andoval (Prolecitha, Dichadena, Lecithophyllum, Syncoelium) stages (Fig. 7; arrangement E). Theseven lobes, whether tubular, digitiform, tear-shaped or oval, may form a rosette arrangement,with three lobes on one side and four on the other, or may form two separate groups of threeand four lobes which are connected by the collecting ducts. Presumably from the latter arrange-ment have developed forms, such as Dinosoma and Arnold, with two vitelline masses which aredistinctly three- and four-lobed (Fig. 7; arrangement F). The lobation then tends to be almost orentirely lost (e.g. Hemiurus, Br achy phallus), resulting in forms, such as Derogenes, Lethadenaand Myosaccium, with two totally unlobed, oval masses. In genera such as Bunocotyle,Monolecithotrema, Monovitella and Chenia the vitellarium is present as a single entire or slightlylobed mass (Fig. 7; arrangement G). This mass was probably, and almost certainly in the lattertwo cases, formed from the fusion of two oval masses ; but there is a possibility that it could bethe result of either the loss of one mass or the condensation of a rosette-arrangement. It must be emphasized here that the above is only a general trend in the form of the vitellarium,as there is a certain amount of variation within each group, particularly within the hemiuridsand the lecithasterids. For example, a relatively common feature of the lecithasterids is a doublingof the number of vitelline lobes. In addition, the number of vitelline tubules or lobes, commonlyseven in many of the hemiuroids, is variable, six, eight or nine frequently being reported. Thepresence of nine (four and five) lobes is especially common on the two vitelline masses of thehalipegine derogenids. As the various links in the above pattern do appear to illustrate the trend relatively clearly,the only real problem is to find evidence which indicates that the follicular arrangement of thevitellarium is primitive. It appears, however, that a follicular vitellarium is found in the majorityof monogenean and cestode groups, in all aspidogastreans and also in some rhabdocoel turbel-larians, e.g. Mesostoma. This suggests very strongly that the follicular arrangement is primitive.It is likely that the duplication of the vitelline glands, resulting in the follicular arrangement,occurred as an early development to accommodate an increase in egg-production. This wouldhave been especially necessary when the 'ancestral rhabdocoel' became an obligate parasite. Thisis emphasized by evidence from the digenean Schistosoma mansoni Sambon, 1907, whichindicates that thirty to forty vitelline cells are present in each egg (Gonnert, 1955). The wide-spread spacial arrangement of this highly metabolically active organ-system in the 'primitive'forms is probably a mechanism to aid the absorbtion of nutrients from the surroundingparenchymatous tissue, rather like the roots of a tree. Even though food is often continuallyavailable to the 'primitive' hemiuroids, such as the azygiids and hirudinellids, they tend to berather large for digeneans, and, therefore, still have certain problems with regard to the diffusionof nutrients. The more 'advanced' hemiuroids tend to be smaller in size, and, therefore, there isno longer such a need for a widespread follicular, dendritic or simple tubular vitelline system,as the problems associated with the diffusion of nutrients are reduced. In addition, there is morecompetition for space, as the uterus tends to take up a much greater proportion of the body.This latter factor, plus the economic advantage in reducing the distance involved in the trans-portation of vitelline material, adequately explains the reduction of the vitellarium to a smallrosette or to one or two masses. One apparent contradiction is the vitelline structure of the syncoeliine syncoeliids, which, asit consists of seven oval lobes, indicates that it is far more 'advanced' than the remainder of the THE HEMIUROIDEA 127 anatomy. The premature reduction in the size of the vitellarium can be explained, however, bycertain modifications in the process of egg-formation which appear to occur in this group. Ourobservations suggest that the eggs of Copiatestes are produced in a uterine ob'type (see glossary),have a membranous 'shell' and contain only one, or a very small number, of vitelline cells.During the egg's passage down the uterus the vitelline cell(s) appear to replicate many times, themembranous 'shell' permitting the diffusion of nutrients into the egg as a source of material andenergy for this process. Not until a full complement of vitelline cells is present, at about themiddle of the uterus, does the egg-shell become thicker, tanned and hardened. The demand onthe vitellarium for vitelline cells appears, therefore, to be greatly reduced, possibly by a factorof twenty to thirty times. Some aspects of egg-shell formation have been described by Gibson(1976) for Copiatestes filiferus (Leuckart, in Sars, 1885) and by Coil & Kuntz (1963) for therelated Syncoelium spathulatum Coil & Kuntz, 1963. 3. Terminal genitalia. The terminal genitalia of the Hemiuroidea show a great number ofmodifications; but do in fact, with a small number of exceptions, illustrate one basic trend. Thereare, however, a number of variations in the general pattern, and it is likely that some features ofthis trend have been evolved independently by parallel evolution. In order to understand boththe nature of the trend and the variation, we must first examine the function of these structures.The function of the male terminal genital apparatus is that of ejecting spermatozoa and enablingit to enter the female system, either of another worm or of the same individual. The function ofthe female terminal genitalia is that of ejecting eggs into the environment, and, we suggest in thecase of the Hemiuroidea, receiving spermatozoa from the male terminal genitalia of eitheranother worm or of the same individual. As indicated above, it is clear from our studies ofLaurer's canal (Gibson & Bray, 1975) that in the Hemiuroidea, when this duct is present, itfunctions as a seminal and vitelline drain, not as a vagina (Trifoliovarium may be an exception).Evidence from the work of Nollen (1968), who used 3 H-thymidine-labelled spermatozoa inPhilophthalmus megalurus (Cort, 1914) suggests that cross-insemination occurs in the majorityof cases whenever possible ; but that, when only single worms are present in a host, self-insemina-tion occurs regularly. Nollen also noted that labelled spermatozoa disappeared from the uterineseminal receptacle within fourteen to sixteen days of copulation, which indicates that repeatedinsemination is required. It would appear, therefore, that self-insemination is a mechanism whichhas evolved to enable lone specimens in a host to produce fertile eggs. It seems very likely that insome genera self-insemination has become increasingly important, to the extent that the malecopulatory apparatus has atrophied. In some cases, such as Bathycotyle, Gonocerca, Aerobiotrema,Syncoelium (sensu stricto) and Tetrochetus, where the copulatory apparatus has completely disap-peared or has been reduced to a vestige, they must, it appears, rely solely upon self-insemination.It is likely that the latter phenomenon has occurred independently in several different groupsboth within and outside the Hemiuroidea. To illustrate this point, the terminal genitalia and theseminal storage and disposal system of the opecoeline opecoelids are almost identical to thosewhich occur in Gonocerca. Too much systematic importance, therefore, should not be placedupon the absence or reduction of the copulatory apparatus. The main trend in the structure of the terminal genitalia of the Hemiuroidea appears to be asfollows. It commences as a simple sinus-organ, produced as a protrusion of the base of thegenital atrium, and containing both of the simple, tubular male and female ducts. These ductscome together and unite near the summit of this organ, forming a short hermaphroditic ductwhich opens via a terminal pore. The close proximity of the male and female ducts which opensinto a common genital atrium aids both reciprocal cross-insemination and self-insemination, and,similarly, the development of an hermaphroditic duct further facilitates self-insemination. Thislatter arrangement (Fig. 8; arrangement A) occurs in the azygiids, where the sinus-organ is ahighly contractile, permanent structure, but is usually found in a relatively contracted state. Thesinus-organ of the azygiids, which presumably acts as a copulatory organ and possibly aids theextrusion of eggs through the genital pore, is formed from the proximal region of the wall of thegenital atrium, and it uses its own intrinsic musculature for extension and contraction. Thegenital atrium presumably serves as a vagina during copulation, and it is likely that the muscular 128 D. I. GIBSON & R. A. BRAY SO B ss aso H Fig. 8 Different arrangements of the terminal genitalia (see text),[aso, amuscular sinus-organ; hd, hermaphroditic duct; so, muscular sinus-organ; ss, sinus-sac.] THE HEMIUROIDEA 129 action of its wall forces the spermatozoa, deposited during copulation, back into the hermaphro-ditic duct through the aperture of the contracted sinus-organ. Following on from the type A arrangement, the sinus-organ becomes a relatively largerstructure in its contracted state, and some of its intrinsic musculature begins to concentrate intoa thin, diffuse sac-like structure surrounding its base (Fig. 8; arrangement B). At the same time,the hermaphroditic duct tends to lengthen, usually reaching at least to the base of the sinus-organ.This arrangement can be seen gradually developing in Prosorchis, Copiatestes, Isoparorchis,Sclerodistomum, Accacoelium and Prosogonotrema, resulting in a type C arrangement (Fig. 8)where the diffuse, muscular thickening at the base of the sinus-organ, which is referred to as thesinus-sac, becomes more apparent in the latter four examples, and, in addition, the intrinsicmusculature of the sinus-organ itself tends to become slightly reduced. We consider that thesinus-sac aids the extrusion of the sinus-organ by exerting hydrostatic pressure upon its contents(Gibson & Bray, 1974). Many of the derogenids tend to have an arrangement very similar tothat of Prosogonotrema, except that the cone-shaped sinus-organ tends to be small. In the dinurinehemiurids the sinus-sac is better developed (Fig. 8 ; arrangement D), becoming an enlarged ovalor tubular structure with a thick, muscular wall, and the sinus-organ is usually cone-shaped, oftenwith a slight reduction in its intrinsic musculature. The sinus-organ may be large, as inParadinurus, or small, as in Dinurus, and it should be mentioned that in a small number ofdinurines, such as Stomachicola, the sinus-organ is absent or reduced to a rudiment: in the lattercases the sinus-sac is also reduced in size. It is noticeable that at about the stage of the type Darrangement, the seminal vesicle, which until now has normally been tubular, tends to becomemore saccular and often develops sphincters and thus becomes partitioned. These appear to bemodifications caused by the fact that, during ejaculation, the spermatozoa now have to beforced into the hermaphroditic duct against the hydrostatic pressure produced when the sinus-sacaids the eversion of the sinus-organ. The next stage (Fig. 8 ; arrangement E) is that the intrinsicmusculature of the sinus-organ is then lost, resulting in the fact that it must be entirely evertedby hydrostatic pressure. This arrangement can be seen in the Elytrophallinae and in the Glomeri-cirrinae, especially in the former, where the sinus-organ appears to be almost totally amuscular,the sinus-sac is well developed and the seminal vesicle is surrounded by an extremely thickmuscular wall. The latter structure is presumably necessary because of an increased hydrostaticpressure necessary to evert the sinus-organ. In the next stage (Fig. 8 ; arrangement F) the genitalatrium is reduced in size and a permanent sinus-organ is lost. The latter is replaced by a short,temporary sinus-organ, rarely seen in fixed specimens, which is formed by evagination of thehermaphroditic duct under hydrostatic pressure. As the hydrostatic pressure is less than thatrequired in the type E arrangement, because of the much smaller sinus-organ and genital atrium,pressure is usually exerted on the seminal vesicle by sphincter muscles or by a thin, muscular layerin its wall, rather than by a thick, muscular wall. This arrangement occurs in the Hemiurinae,Lecithochiriinae, Stomachicola and a small number of related dinurines, the Opisthadeninae, theLecithasterinae and the Quadrifoliovariinae. Finally, in the Hysterolecithinae, Trifoliovariinae,Lethadeninae, Plerurinae, Macradenininae, Dictysarcinae, Prolecithinae and Gonocercinae, thesinus-sac is gradually atrophied (Fig. 8; arrangement G) until in genera such as Aerobiotremaand Gonocerca, it is lost completely (Fig. 8; arrangement H). Presumably, as mentioned above,in the latter groups the ability to cross-inseminate becomes reduced and is finally lost altogether.It is worth noting that there is a slight deviation within the Hemiuridae, in that the Glomericir-rinae, with the type E arrangement, and the Lecithochiriinae, with the type F arrangement, havedeveloped an ejaculatory [prostatic] vesicle. This appears to be a modification of the ejaculatoryduct, the function of which is not known for certain. It may, however, form a temporary storageorgan as part of a mechanism for ejecting larger quantities of spermatozoa during each ejacula-tion. If this is true, then the glandular cells, which often line it, may function, with regard to thestored sperm, in the same way that the pars prostatica does to normal quantities of sperm passingthrough this duct during ejaculation. One group, the Hirudinellidae, stand out as being totally distinct from the remainder of thehemiuroids in that they possess a 'cirrus-sac'. This structure almost certainly developed inde-pendently of the sinus-sac; but it does appear to be analogous. The reason why such a structure 130 D. I. GIBSON & R. A. BRAY has developed in this group is probably because its ancestors lost, or did not develop, anhermaphroditic duct, with the result that the copulatory organ ('cirrus') did not contain thefemale duct. In this group, therefore, both the male and the female ducts have developed theirown finger-like projections from the wall of the genital atrium. It seems certain that the 'cirrus-sac' of the hirudinellids is not homologous with the cirrus-sac which is found in many othergroups of digeneans. At first sight, it is somewhat difficult to see how the hirudinellid arrangementcould have evolved from the type A arrangement; but other morphological features of thehirudinellids suggest a relatively close affinity with some of the other 'primitive' hemiuroids. Forthis reason, it seems unlikely that the hirudinellids split away very early in hemiuroid evolutionbefore the development of an hermaphroditic duct. It is possible, however, to envisage thegradual separation of the male and female ducts of the type A arrangement, where the hermaphro-ditic duct is short, much in the same way as appears to have occurred in some species of Halipegus,where the two ducts open separately at the end of the sinus-organ. It is very unlikely that theHirudinellidae resemble the ancestral form of the hemiuroids, as it is difficult to imagine how anhermaphroditic duct could have been derived from the hirudinellid arrangement. We can assume that the presence of apparatus well adapted to enable cross-insemination tooccur is the primitive condition in the hemiuroids, as cross-insemination occurs in all othergroups of helminths. Even in the primitive hemiuroids, however, it is almost certain that self-insemination does occur, and Dawes (1946) notes that self-insemination of lone specimens of theaspidogastrean Aspidogaster conchicola has been observed. It seems likely that the type Aarrangement in our trend is primitive. It is a fact that the majority of hemiuroids differ from themajority of helminths in that the copulatory organ is not the usual cirrus, which is often enclosedby a cirrus-sac. Nevertheless, all of the structures termed 'cirrus' are not homologous, as thecopulatory organs of many groups of animals have a phallic appearance. In addition, it is un-likely that all of the structures termed 'cirrus-sac' are homologous, as similar 'sacs' surround thebase of, and are associated with the protrusion of, many eversible organs, e.g. the proboscis sacof the Acanthocephala. If we examine the aspidogastreans, the majority of species do possess acirrus-sac, but several do not. There appears to be no evidence in the latter group for the presenceof an hermaphroditic duct. As it seems difficult to envisage the development of an hermaphroditicduct, similar to that occurring in the hemiuroids, from a form with a cirrus-sac, it is possible thatthe rhabdocoel-like ancestors of the digeneans possessed a temporary penis-papilla ('cirrus'),lacking a penis-bulb ('cirrus-sac'), which was formed from the wall of the genital atrium. Com-mencing with such a structure, it is possible to envisage the development of all of the variationsof the terminal genitalia which occur in the Digenea and Aspidogastrea. A suggested evolutionary scheme within the Hemiuroidea Published works on evolution within the Digenea are few. Aspects of this subject have beendiscussed by workers such as Odening (1974), and detailed comments on particular groups havebeen given by others, such as Bayssade-Dufour & Maillard (1974); but only a few workers, suchas Poche (1926) and Cable (1974), appear to have indicated detailed evolutionary relationshipswithin the Digenea as a whole. The majority of evidence in the more recent work has come fromlarval morphology and details of the life-history. As discussed in our introduction, we believethat much of the evidence based upon such information is questionable. Admittedly data fromthe intra-molluscan stages are likely to be of some value, but only at the higher taxonomic levels,and, as indicated on p. 38, there are some anomalies. If, as Rohde (1972) suggests, the cercariaewere 'invented' by the digenean ancestors as a mechanism to aid the transmission from themolluscan host to the vertebrate host, evidence based upon cercarial morphology, especially asthis larval stage is more susceptible to environmental changes than the others, is somewhatdubious. Although the majority of phylogenetic hypotheses on the evolution of and within theDigenea have been based upon larval characteristics, there is evidence that workers are beginningto reappraise the value of adult morphology. Powell & Sogandares-Bernal (1970), for instance,stated: 'While on the subject of larval trematodes, the systematic value of comparative anatomicalstudies of the terminal genitalia and sensory structures of adult worms should be emphasized. THE HEMIUROIDEA 131 Homologies and analogies of terminal genitalia (for example in the Hemiuroidea) should proveuseful in determining phylogenetic relationships.' Using evidence outlined in the trends illustrated above, we have attempted to build a hypo-thetical picture of the evolution of the Hemiuroidea. Our proposed relationships are expressedin Fig. 9. We believe that the most primitive groups are the azygiids and the ptychogonimids, andthat the most closely related of these to the ancestors of the remainder of the hemiuroids appear tobe the leuceruthrine azygiids. These groups exhibit a combination of primitive characters, suchas a follicular vitellarium, a sinus-organ without an accompanying sinus-sac and with Laurer'scanal acting as a seminal and vitelline drain. The Leuceruthrinae, which appears to exist as asingle species, possesses the same gonadal arrangement as that which occurs in the vast majorityof the remainder of the hemiuroids. Another interesting feature which may indicate primitivenessin this group is that in known azygiid life-cycles the cercariae are eaten directly by the definitivehost. This suggests the possibility that the azygiids evolved before the acquisition of the secondintermediate host which occurs in most digenean life-cycles. Other primitive groups are theHirudinellidae, Bathycotylidae, Isoparorchiidae, Syncoeliidae, Accacoeliidae and Sclerodisto-moididae, and it seems likely that they, especially the latter four, have arisen from a commonancestor. Nevertheless, there are features of the syncoeliids, such as the presence of sevenvitelline lobes in the syncoeliines, which suggest that they are more advanced than indicated bythe position which we have allocated to them in our 'evolutionary picture'; but, as discussedabove (p. 126), these anomalies can be explained. In the latter groups a sinus-sac develops (a'cirrus-sac' in the case of the hirudinellids) and the vitellarium becomes tubular. In our opinionthe remainder of the hemiuroids have evolved from an ancestor resembling the present-daysclerodistomids, although most probably lacking Manter's organ and with more posteriorlysituated gonads. From this ancestral form, which presumably possessed a vitellarium consistingof seven tubules, a well-developed sinus-organ and sinus-sac, and Laurer's canal (which althoughopening dorsally was on the point of evolving a rudimentary Juel's organ), four main lines appearto have evolved. These are: (1) the modern members of the Sclerodistomidae; (2) the Derogenidae;(3) the Lecithasteridae, Dictysarcidae and the Didymozooidea (see p. 133); and (4) the Hemi-uridae and Bunocotylidae. The development of Juel's organ, in the rudimentary and or thefully developed form, has occurred in all of these groups. As forms with Laurer's canal openingdorsally also occur in three of the groups, it seems more likely that Juel's organ has arisen inde-pendently by parallel evolution than by the concurrent evolution of forms with and without thisorgan in all of these three groups. The sclerodistomids are the only one of these groups which either have not developed acomplete Juel's organ or in which no members of the group possessing such an organ survive,although rudimentary forms occur in Prosogonotrema and Prosorchis. It would appear that despitethe position of the gonads, the prosogonotrematine and prosorchiine genera are perhaps moreclosely related to the other three groups outlined above than the sclerodistomines. The Derogenidae are a very successful group with a complex mixture of primitive and advancedfeatures, especially with regard to the nature of the seminal storage and disposal apparatus in thefemale reproductive system. Nevertheless, the majority of members tend to be relatively similarin gross morphology, although it seems likely that the three subfamilies of this group separatedquite early in the evolution of the group. They probably owe their success to the fact that theytend to fill niches where competition is somewhat reduced, i.e. the stomach of oceanic fishes, inthe case of the Gonocercinae and the Derogeninae, and both the stomach of brackish water andfreshwater fishes and the mouth and eustachian tubes of amphibians, in the case of theHalipeginae. The Lecithasteridae appear to have evolved via forms similar to Trifoliovarium, but stillretaining a uterine seminal receptacle and a rudimentary seminal receptacle. From this formdeveloped the modern members of the Trifoliovariinae and, after the independent formation ofJuel's organ, the Hysterolecithinae. The remainder of the lecithasterids could have evolved fromforms similar to Trifoliovarium by the loss of Laurer's canal, much in the same way asCladolecithotrema has probably developed ; but it seems more likely that they have evolved fromhysterolecithine ancestors. This is suggested by the great morphological similarity between the 132 D. I. GIBSON & R. A. BRAY Fig. 9 A suggested evolutionary tree for the Hemiuroidea. THE HEMIUROIDEA 133 Hysterolecithinae and some of the other lecithasterids and because the thick-walled nature ofthe blind seminal receptacle in the rest of the lecithasterids suggests that it might have evolvedfrom Juel's organ by hypertrophy of the 'inner vesicle'. It is also apparent, because of thepresence of Juel's organ and other morphological similarities, that not only the Dictysarcidae,but also the Didymozooidea (see below), may have evolved from hysterolecithine ancestors. In the largest group, the Hemiuridae, an ecsoma in association with a plicated tegumentappears to have developed (see p. 41), although the former is occasionally reduced and thelatter is often completely lost. These adaptations appear to be associated with the hostile habitatof the majority of hemiurids, the stomach of marine teleosts which is a region of variable pHand osmolarity. The most primitive group appears to be the Dinurinae, some of which havefeatures in common with some of the modern sclerodistomids, although all appear to possess afully developed Juel's organ. The dinurines probably gave rise to the elytrophallines by thedevelopment of an amuscular sinus-organ and associated changes in the seminal vesicle. Theelytrophallines could then have given rise to: (1) the Glomericirrinae, by the development of anejaculatory (prostatic) vesicle, which in turn gave rise to forms, such as the Lecithochiriinae, bythe loss of a permanent sinus-organ; and (2) the Hemiurinae and the Lethadeninae, by the lossof a permanent sinus-organ. The Bunocotylidae appear to have evolved from ancestral hemiurinesby the loss of the ecsoma. It is worth noting that some members of the Aphanurinae still retaina plicated tegument. In the members of the Bunocotylinae, which are extremely small, Juel'sorgan appears to have been lost, there apparently being no obvious mechanism for disposing ofexcess seminal and vitelline material. It is possible that these compact and apparently advancedworms utilize not only space, but also spermatozoa and vitelline material, more efficiently, thusreducing the value such a specialized organ. In the opisthadenines Juel's organ appears to havedeveloped into a blind seminal receptacle, much in the same way as we suggest it developed inthe majority of the lecithasterids. Throughout the evolution of this group it is clear that there is a general decrease in body-size,ranging from the giant azygiids and hirudinellids to the minute bunocotylids. Associated withthis decrease in size is a more efficient utilization of body-space, such as the development of acompact vitellarium, and a more efficient utilization of excess reproductive products. In addition,although less certain, there appears to be an increase in the proportion of the body occupied bythe uterus, and an increase in the dependency upon self-fertilization, thus reducing the need forlarge and complex terminal genitalia. Some comments on the relationship of the Didymozooidea and the Paramphistomoidea to theHemiuroidea The Didymozooidea are a group which several early workers, such as Odhner (1907) and Poche(1926), considered to be evolved from hemiuroid stock. This early work was based upon adultmorphology. Baer & Joyeux (1961), however, basing their hypothesis on the work of Ishii (1935)which indicated that adults of this group developed directly from eggs, recognized theDidymozoidea as a new subclass, distinct from the Digenea, within the class Trematoda. RecentlyCable (1955, 1974), using evidence from larval stages, has reiterated Odhner's initial hypothesisthat this group is derived from hemiuroid stock. Skrjabin (1955) and Yamaguti (1971) present thedidymozooids as a distinct suborder and superfamily, respectively, to the hemiuroids, but donot comment on any relationship between the two. If those didymozooid genera with a simpler and more conventional morphology, such asNematobothrium van Beneden, 1858,* are examined, several similarities with the hemiuroids areapparent. The testes are normally pre-ovarian and the ovary normally occurs anterior to thevitellarium. The male and female terminal ducts fuse, often forming a short hermaphroditic duct,and open via a common genital pore, and in some instances a small terminal papilla not unlikea sinus-organ is present. In addition, the shape and arrangement of the gonads in juvenile speci-mens of Didymocystis acanthocybii Yamaguti, 1938 (as figured by Yamaguti, 1970), are very * The conception of the genus used here is that of Yamaguti (1971). 134 D. I. GIBSON & R. A. BRAY similar to those of the dictysarcid hemiuroid Elongoparorchis. More convincing, however, are thefacts that a uterine seminal receptacle is present in Nematobothrium robustum Yamaguti, 1970,and that Odhner (1907) has described what appears to be a well-developed Juel's organ in theclosely related N. scombri (Taschenburg, 1879) (Fig. 10A). Although the latter structure inNematobothrium spp. has usually been referred to as a seminal receptacle, Yamaguti (1970),when describing Neonematobothrioides poonui, noted that it contained germ-cells and vitellinematerial, in addition to spermatozoa. An apparent Juel's organ was also seen by Dollfus (1935)in Nematobothrium pelamydis (Taschenburg, 1879). Juel's organ of the didymozooids appears todiffer slightly from that in the hemiurids, for example, in that the 'inner vesicle' is not completelyenclosed proximally by the outer region of the organ, suggesting that it is perhaps slightly moreprimitive (see p. 121). The presence of Juel's organ and a uterine seminal receptacle, however,does not appear to be the usual condition in the more highly developed didymozooids. In themajority of these cases the uterine seminal receptacle has apparently been lost and Juel's organappears to have become transformed into a blind seminal receptacle, which is connected to theoviduct by a short duct, much in the same way as blind seminal receptacles have probably beenformed in the majority of lecithasterids and the opisthadenine bunocotylids. In sections of anunidentified didymozooine [close to Didymocystis Ariola, 1902] from Katsuwonus pelamys offPapua New Guinea, the outer half of the blind seminal receptacle has a thick wall, possibly beingthe vestige of the outer region of Juel's organ, and the inner half (that closest to the duct) of thisseminal receptacle has a thin wall, possibly being formed from the part of the 'inner vesicle' notenclosed by the outer region of Juel's organ (Fig. 10B). These observations on the gross morphology and on the nature of the seminal storage anddisposal apparatus in the proximal female reproductive system of certain didymozooids suggestto us that this group did evolve from hemiuroid stock close to the origins of the Dictysarcidaeprobably from an ancestral form of hysterolecithine lecithasterid (see Fig. 9). B bsr t w Fig. 10 Parts of the seminal storage and disposal apparatus in the female reproduction system oftwo didymozooids: A. Nematobothrium scombri (modified after Odhner, 1907); B. Unidentifieddidymozooine. [bsr, blind seminal receptacle; eiv, external 'inner vesicle'; iiv, internal 'innervesicle'; Jo, Juel's organ; tw, thick-walled region of blind seminal receptacle.] THE HEMIUROIDEA 135 It is also worth noting that there are certain morphological features which suggest that theremay be affinities between the paramphistomoids and some of the more primitive hemiuroids.These include a follicular vitellarium, the absence of a prepharynx, paired testes which are usuallypre-ovarian, the presence of Laurer's canal in association with a uterine seminal receptacle andsimilar terminal genital apparatus. The paramphistomoids differ fundamentally in adultmorphology only in the fact that the excretory pore is dorsal rather than being terminal. Althoughthe hindbody is almost absent in this group, there is also a tendency for its reduction in certainhemiuroids, especially in the Sclerodistomidae. The paramphistomoids are generally considered tobe stomach parasites of terrestrial vertebrates: several genera have, however, been recorded fromteleosts. One particular group, the Brumptiidae Stunkard, 1925, appears to be morphologicallyvery similar to the hemiuroids in that its members possess a well-developed sinus-sac and anhermaphroditic duct, and, in the lateral fields, there is a distinct hindbody present in the form oflobes, being somewhat similar to, but smaller than, those which occur in the syncoeliid Otiotrema. Although workers such as Dawes (1936) have considered the paramphistomoids to be veryprimitive, Cable (1974) places this group well up one of the branches of his evolutionary tree.He also places it on quite a distinct branch to the hemiuroids, although Poche (1926) had placedthem much closer together. Evidence from adult morphology suggests that the paramphistomoidsmight have been derived from hemiuroid stock close to the point where the syncoeliids andhirudinellids evolved. Nevertheless, there does appear to be fundamental differences in themorphology of the larval stages and the life-history which tend to preclude any serious con-sideration of this relationship until the significance of these differences is fully understood. Acknowledgements We would like to take this opportunity of thanking the following people who have helped uswith various aspects of this work: Mr T. Bakke (Zoologisk Museum, Oslo), Dr I. Ball (Universityof Amsterdam), Professor A. Brinkmann Jr (University of Bergen), Dr A. V. Gaevskaja(AtlantNIRO, Kaliningrad), Dr S. Kamegai (Meguro Parasitological Museum, Tokyo), Dr R.Lichtenfels (USDA, Beltsville, Maryland), Professor P. Nasir (Universidad de Oriente,Venezuela), Professor O. Nybelin (Natural History Museum, Gothenburg), Dr R. Overstreet(Gulf Coast Research Laboratory, Ocean Springs, Mississippi), Dr M. H. Pritchard (H. W.Manter Laboratory, University of Nebraska) and Mr J. Thulin (University of Gothenbuig). Weare also indebted to Mr D. W. Cooper and Mr S. J. Moore for the preparation of many hundredsof sections, to Mrs H. Sabo for translating various Russian papers and to Miss J. S. Williamsfor help with the final copies of the illustrations. References Acena, S. P. 1947. New trematodes from Puget Sound fishes. Trans. Am. microsc. Soc. 66 : 127-139.Agrawal, V. 1966. Studies on some trematode parasites of fresh water fishes of Lucknow. Annls Parasit. hum. comp. 41 : 217-231.Ahmad, J. 1977. Two new species of digenetic trematodes of fishes from the Bay of Bengal. Neth. J. Zool. 27 : 305-309.Amato, J. F. R. 1968. Contribuicao ao conhecimento da fauna helmintologia do Rio Grande do Sul. Um novo parasito de peixe cascudo Plecostomus commersoni (Cuv. & Val.) (Trematoda, Hemiuroidea). Revta bras. 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Trustees of the British Museum (Natural History), 1979 ISSN 0007-1498 Zoology series Vol 36 No 3 pp 147-200 British Museum (Natural History) Cromwell Road London SW7 5BD Issued 27 September 1979 Notes on the anatomy of Macrochirichthysmacrochirus (Valenciennes), 1844, with comments onthe Cultrinae (Pisces, Cyprinidae) G. J. Howes Department of ^Zoology, British Museum (Natural History), Cromwell Road, London SW7 5BD Contents Introduction ............ 147 List of study material ........... 147 Abbreviations used in text figures ......... 149 Anatomical notes on Macrochirichthys macrochirus . . . . . . 150 Cranium ............. 150 Circumorbitals ............ 157 Intermuscular bones and the epaxial musculature . . . . . . 158 Vertebral column . . . . . . . . . . .162 Jaws ............. 172 Suspensorium and associated musculature 173 Pectoral girdle and associated cranial bones 177 Abdominal keel and scale rows ......... 180 Discussion ............. 181 Functional morphology . . . . . . . . . .182 Relationships of Macrochirichthys ........ 185 The cheline group; taxonomy and interrelationships . . . . . 187 Comments on the Cultrinae and its relationships with the cheline group . . 193 Conclusions 198 Acknowledgements ........... 199 References 199 Introduction The purpose of this paper is three-fold; to describe certain anatomical features of the piscivorouscyprinid Macrochirichthys macrochirus, to account for their structure in terms of function, andon the basis of those features considered to be derived ones, to postulate the taxon's relationships.The identification and assessment of these characters has led to a reappraisal of the Cultrinae,the subfamily to which Macrochirichthys is presently assigned, and to the delimitation of amonophyletic assemblage which includes Macrochirichthys but excludes many of the generacurrently placed in the Cultrinae. In an earlier paper describing in part the musculature and skeletal elements of Macrochirichthys(Howes, 1976), I pointed out a convergence (see p. 184) between this species and the characoidRhaphiodon. The present studies (on Macrochirichthys) enable further comparisons to be made ofskeletal and myological architecture in these two cypriniform genera. Nomenclatural note The relatively unfamiliar generic name Securicula Giinther 1868 is introduced early in this paper.This name is used in place of Pseudoxygaster Banarescu 1967 for which reasons are stated onp. 191. List of study material Much of the material listed in a previous study (Howes, 1978) was re-examined and only additionalspecimens used for the present study are given here. Bull. Br. Mus. nat. Hist (Zool.) 36 (3) : 147-200 Issued 27 September 1979 THE ANATOMY OF MACROCHIRICHTHYS MACROCHIRUS 149 BMNH register number Locality Species Salmostoma bacailaSalmostoma bacailaSalmostoma boopisSalmostoma clupeoidesSalmostoma phulo phuloSalmostoma phulo phuloSalmostoma phulo orissaensisHolotype Salmostoma phulo orissaensisParatype Salmostoma sardinellaSalmostoma untrahiSalmostoma untrahiSecuricula goraSecuricula goraSecuricula goraSecuricula gora Toxabramis swinhonis(Syntypes) Xenocypris davidiXenocypris tumirostrisXenocypris yunnanensis All the specimens were dissected and radiographed. Deoli, IndiaCentral Prov.CanaraDarna R.Godavery R.Assam Orissa OrissaSittany R.Mahannddi R.OrissaAssamAllahabadUnknownUnknown Shanghai SzechwanSzechwanYunnan L. Standard length (mm) Alizarin c. 75 106,113,52 77 192-82 84 54 54 45 96-95 94 65-90 126 138 170 Alizarin 93 77-80 22422790 Abbreviations used in the text figures AA Anguloarticular AS Axial scale BO Basioccipital CCF Cleithrum-coracoid fenestra CF Carotid foramen CL Cleithrum CIM Cranial intermuscular bones (numbered) COR Coracoid D Dentary Depx Dorsal section of epaxialis muscle ECT Ectopterygoid ENT Entopterygoid EPO Epioccipital ES Extrascapular Ets Tendinous midline septum of epaxialis EXO Exoccipital FC Frontal sensory canal FR Frontal F IV Foramen for trochlear nerve F V Foramen for trigemino-facialis trunk Hlms Horizontal lateral myoseptum HMP Hyomandibular process Hms Medial segment of hypaxialis muscle HY Hyomandibula Hypx Hypaxialis muscle IF Infraorbitals (numbered) KE Kinethmoid Lap 1 , 2 Levator arcus palatini muscle, divisions 1 and 2 LE Lateral ethmoid Lepx Lateral epaxialis muscle LIM Lateral intermuscular bones LKE Kinethmoid-mesethmoid ligament LP2 Lateral process of 2nd vertebra Ls Lateralis superficialis muscle ME Mesethmoid MQF Metapterygoid-quadrate fenestra Ms Myosepta MX Maxilla NC Neural complex NP2 & 3 Neural process of 2nd and 3rd vertebrae NS Neural spine (numbered) Obi Obliquus inferioris muscle Obs Obliquus superioris muscle OP Operculum OS Os suspensorium 150 PA Parietal PAL Palatine PAS Parasphenoid PC Postcleithrum PCP Posterior coracoid process PE Preethmoid PMX Premaxilla PRO Prootic PTS Pterosphenoid PTT Posttemporal Q Quadrate QF Quadrate foramen RA Retroarticular SC Supracleithrum Sea Supracarinalis anterior muscle SE Supraethmoid G. J. HOWES SN Supraneural (numbered) SO Supraoccipital SOR Supraorbital SPO Sphenotic SY Symplectic TR Tripus Tsca Tendon of supracarinalis anterior muscle V Vertebra (numbered) Vebx Ventral section of epaxialis muscle VC1 Cartilage block between ventral process of 1st vertebra and limb of 2nd vertebraVO Vomer X Axis of vertebral column Anatomical notes on Macrochirichthys macrochirus After each descriptive section there follows a comparison, with other cultrine and in some cases,non-cultrine genera. The most outstanding features of Macrochirichthys are the almost straight to convex dorsalhead profile, the oblique angle of the mouth and the greatly extended pectoral fins (Fig. 1). Thebody is elongate, tapering caudally and is markedly compressed with a prominent ventral keel;the scales are small, c. 120 in the lateral line, the lateral line is curved gently downwards and runsalmost midlaterally; the dorsal and anal fins are placed far back; the length of the pectoral fin isalmost twice that of the head and its tip extends to a point nearly half-way along the standardlength; the pelvic fins are situated midway between the base of the pectorals and the origin of thecaudal fin. The fish is intensely silver along the flanks, brassy dorsally and with a large blackblotch at the base of the caudal fin. Juvenile specimens possess dark saddle-like markings betweenthe head and the dorsal fin. Smith (1945) reports specimens of more than half a metre in length. There appears to be only a single species referrable to this genus (see Smith 1945 : 77-78 andp. 187). It is recorded from Thailand, Java, Sumatra, Borneo, Cambodia, Laos and south China(Weber & De Beaufort, 1916; Smith, 1945; Wu, 1964; Taki, 1974). 20mmFig. 1. Outline drawing of Macrochirichthys macrochirus. Cranium The horizontal dorsal outline of the head does not indicate the top of the cranium but marks theedge of the thick wedge of epaxial muscle mass that extends forward as far as the anterior borderof the frontals. The cranium itself is aligned at an angle of 20 to the vertebral column (seep. 171). The skull is narrow and is, to the best of my knowledge, the most compressed in anycyprinid. The frontals curve medially so as to form an elongate basin into which the epaxial muscle massinserts (Fig. 2A). Laterally, each frontal is folded over to form a creased edge. Anteriorly the THE ANATOMY OF MACROCHIRICHTHYS MACROCHIRUS 151 A B C Fig. 2 Cross-sections of the crania of A. Macrochirichthys macrochirus. B. Securicula gora. C.Parachela oxygastroides. Two sections are shown, through the sphenotic region (entire outline)and through the anterior part of the ethmoid region (inset outline). The extent of the frontalsare indicated by the thickened line. frontals overlie the supraethmoid and cover that bone almost to its anterior margin (see below).In adults the frontal sensory canals converge to share a common opening at the midline (Fig. 3).In juveniles (30 mm SL) the frontals have not developed the concavity seen in the adult but areflat and the epaxial musculature extends only as a thin band along the midline to the anterior tipof the bones. Furthermore, at this stage of development the frontals have not extended forward tocover the supraethmoid and the sensory canals do not meet (cf. Figs 3 & 4). For the ethmoid region the use of the terms supraethmoid and mesethmoid follows that ofWeitzman (1967), Patterson (1975) and Dornesco & Soresco (1971). The supraethmoid is the SE ME KE 3mm Fig. 3 Macrochirichys macrochirus ethmo-vomerine region in A. Dorsal view. B. Lateral view. 152 G. J. HOWES dermal bone overyling the ethmoid cartilage and in small specimens can be clearly distinguishedas a separate element (see below); in some larger specimens although its anterior and lateralsutures can be denned, the supraethmoid is more often than not fused with the underlying, andossified, ethmoid cartilage (mesethmoid). The term ethmoid block is used here to denote theentire unit comprising the supraethmoid, mesethmoid and preethmoids. In adult Macrochirichthys the supraethmoid is short, barely projecting from below the frontals.Its anterior border is concave; on either side protrudes the forwardly curved mesethmoid; thusthe entire region presents a concave anterior face which slopes downward to join the underlyingvomer (Fig. 3). The vomer extends anteriorly well beyond the mesethmoid and is deeply notched (Fig. 3).Posteriorly it extends to below the suture of the mesethmoid with the lateral ethmoids. Laterally,the lower part of the mesethmoid and the upper part of the vomer are recessed to receive thewedge-shaped preethmoids. ME FC SE 1mm Fig. 4 Macrochirichthys macrochirus. Dorsal view of the anterior part of the cranium of a juvenile (30 mm SL). In specimens of 30 mm SL the shape of the ethmoid block differs from that in the adult (Fig 4).The supraethmoid is well-defined and is covered by the frontals only along its V-shaped posteriormargin ; the anterior concavity of the ethmoid block is far more pronounced, with a greateranterior and lateral extension than in adult specimens. The vomer is exposed below the anteriorextensions of the ethmoid block and is not visible in the midline when viewed from above. The kinethmoid (Figs 3 & 5A) fits into the anterior ethmoid notch, its contacting face curved inboth the vertical and transverse planes. Dorsally the kinethmoid is expanded into two lateralwings which curve forward to enclose the tips of the premaxillary ascending processes. Twoligaments connect the kinethmoid to each face of the mesethmoid. The depression of the cranium has resulted in the orbitosphenoids being shallow and in closecontact with the parasphenoid. Contact is via a septum derived mainly from the orbitosphenoidsand only partly from the parasphenoid. The postero-ventral border of each pterosphenoid contacts the respective ascending process ofthe parasphenoid; the posterior border is bounded by the prootic and the sphenotic (Fig. 6). The prootic is a long, depressed bone bearing a long lateral commissure across the trigemino-facialis chamber, the anterior foramen of which is situated on the border of the prootic (Fig. 6). The sphenotic is narrow and is curved downwards as an almost perpendicular surface. Thesphenotic process, which in most cyprinids extends laterally as a thick spine, is here developed as awide, ventrally directed arm (Fig. 6). Each parietal covers an extensive area of the cranium, overlying the medial part of the pteroticso that it extends to the lateral edge of the cranium (Fig. 6). The supraoccipital is a large bone with a shallow medial ridge extending posteriorly as alamellar process. On either side of the ridge the supraoccipital is formed into a hummock. THE ANATOMY OF MACROCHIRICHTHYS MACROCHIRUS 153 1mm Fig. 5 Kinethmoids of A. Macrochirichthys macrochirus, B. Securicula gora, C. Parachela oxygas-troides, D. Chela laubuca, E. Danio malabaricus. Lateral oblique views. The subtemporal fossae have considerable depth because of the high vaulting of the craniumin the parietal-supraoccipital region. Posttemporal fossae are absent. Comments and comparisons The overlapping of the supraethmoid by the frontals is a character shared with Securicula,Salmostoma, Chela, Aspidoparia, Rasborinus and some species of Rasbora and Danio. In all othercyprinids I have examined the supraethmoid meets the leading edge of the frontals in a closesuture. An exception is in some species presently assigned to the African genus Engraulicypris;work is in progress on this group and for the time being it can be stated that the presence of thisfeature in 'Engraulicypris' is considered a parallelism. The supraethmoid of Securicula is larger than that of Macrochirichthys, its anterior border isconvex and, furthermore, the arms of the ethmoid block do not diverge to the same extent (Fig. 7).A similar type of morphology to that of Securicula is found in Salmostoma, while in Oxygaster CIM EPO PTE EXO PRO PAS PTS Fig. 6 Macrochirichthys macrochirus, lateral view of the posterior neurocranium. 154 G. J. HOWES FR Fig. 7 Securicula gora, ethmo-vomerine region in dorso-posterior oblique view. Vomer separated from mesethmoid. the narrow supraethmoid with its concave border and the diverging arms of the underlyingmesethmoid more closely resemble the condition in Macrochirichthys. In Chela the supraethmoid is a narrow, axe-shaped bone covering only the medial area of theunderlying mesethmoid (Fig. 8). The mesethmoid projects far beyond the lateral edges of thesupraethmoid (a condition encountered in juvenile Macrochirichthys, see above, p. 152). Antero-ventrally the ethmoid block extends forward as a thin shelf; the vomer is considerably reduced inthickness and lies as a thin plate below the medial and lateral ethmoids with only its posteriormargin contacting the parasphenoid. Fig. 8 Chela laubuca, ethmo-vomerine region in A. Dorsal, B. Lateral views. THE ANATOMY OF MACROCHIRICHTHYS MACROCHIRUS 155 The morphology of the ethmo-vomerine region of some Rasbora species resembles that inChela, particularly in the development of the thin ethmoid shelf and the kinethmoid (see below). In other cultrines (e.g. Culler and Erythroculter) the supraethmoid is thick and posteriorly issutured to the frontals (Fig. 9A). The mesethmoid is long and overlies the vomer for most of itslength. The preethmoids are large and extend to beyond the border of the vomer. A similarcondition exists in Pseudolaubuca but here the entire ethmoid block is deepened (Fig. 9B). Asimilarly deep ethmoid region is found in Pelecus (Fig. 9D). The morphology of these cultrinegenera differs from that in other cyprinids (exemplified by Opsariichthys, Fig. 9C) where thevomer is exceedingly thick, the supraethmoid is reduced in length (but wide and laterally over-lapping the mesethmoid) and the preethmoids extensive. D Fig. 9 VO Ethmo-vomerine regions of A. Culler alburnus, Pseudolaubuca sinensis, C. Opsariichthysuncirostris, D. Pelecus cultratus. Lateral views. The dorsal expansion of the kinethmoid found in Macrochirichthys is also present in Oxygaster(Fig. 5C); in some species the lateral wings of the kinethmoid project anteriorly to articulate withthe premaxillaries, as in Macrochirichthys (Fig. 5A). In Securicula there is no great dorsal expan-sion of the kinethmoid; instead small extensions are present on either side and serve for theinsertion of the ligaments connecting the bone to the mesethmoid (Fig. 5B). However, theanterior tip of the kinethmoid is convex instead of concave (as it is in Macrochirichthys andOxygaster} and it is connected with the premaxillaries via ligaments and not direct bony projec-tions. In Chela and Rasbora (some species) the kinethmoid is lamellar and broadly triangular,and its dorsal border is concave (Fig. 5D). In these taxa the bone is inclined backward and liesagainst the protruding shelf when the jaws are opened. Although in Danio (some species) thetriangular outline of the bone is preserved, the kinethmoid is modified into a bow-shaped structure(Fig. 5E). The medial depression of the frontals is a character shared with three other genera, Securicula,Oxygaster and Pelecus. However, in Securicula the frontals are wider and the medial depression 156 G. J. HOWES shallower; also, the lateral edges of the frontals are curved upwards and the inner branch of thefrontal sensory canal is curved mesially to meet its counterpart some-way back from the anterioredge of the bone (Fig. 10). Of the five species assigned to the genus Oxygaster (see Banarescu,1969), all apart from O. anomalura share with Macrochirichthys the same narrow and deeplydepressed frontals; likewise the frontal sensory canals converge anteriorly to share a commonopening. In Oxygaster anomalura the frontals are flat without the medial groove and the sensorycanals are confined to the lateral edges of the bones. In Pelecus, although the frontals bear adepression similar to that of Macrochirichthys they do not overlap the supraethmoid anteriorly;also, the sensory canals are restricted to the lateral margins of the bones and are much ramifiedand, furthermore, the frontals partly cover the sphenotic so as to form a roof for the dilatatorfossa. The dilatator fossa in Macrochirichthys is not roofed and in Securicula and Oxygaster it isoverlapped by the pterotic. SPO PTE PIT FR FC PA SO Fig. 10 Securicula gora, dorsal view of cranium. In Securicula the sphenotic bears a small, laterally directed process (Fig. 10). A similar process!s also present in Oxygaster but is directed ventro-posteriorly. The pterotic in Securicula con-tributes more to the dorsal surface of the cranium than it does in Macrochirichthys and Oxygaster,and the posterior region of the skull is not so highly vaulted (Fig. 10). In Chela and Salmostoma the parasphenoid and the orbitosphenoids are linked by a deeporbitosphenoid septum. In Macrochirichthys, Securicula and Oxygaster these bones are closelyunited. Mention of this feature was made by Howes (1978) and it has been noted that in otherostariophysans such close contact between the orbitosphenoids and parasphenoid is associatedwith a large gape (Howes, 1976; Menezes, 1976). There is an obvious functional advantage insuch an arrangement; the area of the palatoquadrate arch is increased by moving the para-sphenoid dorsally, while there is a concomitant increase in the volume of the buccal cavity. Theclose association of the parasphenoid with the cranial roof may serve to distribute the stressesimposed upon the cranium through the striking-type feeding action of these fishes. Althoughfunctional demands have undoubtedly influenced the development of this type of bone association,the degree of separation between the bones may well reflect phyletic affinities. Certainly in allspecies of Salmostoma there is a deep orbitosphenoid septum regardless of gape size, whichshows interspecific variation. In Macrochirichthys there is a lateral connection between the pterosphenoid and the ascendingwing of the parasphenoid (p. 152, & Figs 6 & 1 1). This type of connection is encountered rarely inthe cyprinids (see Howes, 1978). It occurs in some species of Barilius and Luciosoma but in thegroup of genera presently under discussion it occurs only in Securicula. In this taxon the connec-tion between the two bones is extensive (reminiscent of the condition in some Barilius). A featureSecuricula shares with Salmostoma is that the anterior trigemino-facialis foramen is situatedwithin the face of the prootic and the lateral commissure is narrow. There is no connectionbetween the parasphenoid and pterosphenoid in Salmostoma, Oxygaster or Chela, the ptero-sphenoid contacting only the prootic posteriorly (Fig. 11). Current studies on the bariliines and THE ANATOMY OF MACROCHIRICHTHYS MACROCHIRUS 157 other cyprinids indicate that the lateral connection of the pterosphenoid and parasphenoid is aderived feature. It is usually achieved through a backward lengthening of the pterosphenoid andonly a slight forward extension of the prootic. This forward movement of the prootic involvesthe wall anterior to the trigemino-facialis foramen and thus the foramen becomes placed withinthe prootic face (the condition encountered in Securicula). Macrochirichthys is unusual in thatthere has been no anterior lengthening of the prootic but a marked posterior extension. This hasresulted in a long lateral commissure, but the anterior foramen of the trigemino-facialis chamberhas remained on the border of the bone. It is also noted that there has been only a slight posteriorextension of the pterosphenoid. PTS PRO B PTS Fig. 11 Outline figures of prootic-pterosphenoid-parasphenoid junction in A. Salmostoma bacaila,B. Securicula gora, C. Chela laubuca, D. Oxygaster anomalura, E. Parachela oxygastroides, F.Macrochirichthys macrochirus. In summary; the medially depressed cranium is a feature Macrochirichthys shares withSecuricula, all but one species of Oxygaster and Pelecus. Pelecus, however, does not share withthe others the overlap of the supraethmoid by the frontals. Macrochirichthys shares with all butone species of Oxygaster the convergence of the frontal sensory canals and with Securicula alateral connection between the pterosphenoid and parasphenoid. Circumorbitals (Figs 12 & 13) The supraorbital of Macrochirichthys is reduced in the adult to a barely detectable splinter thathas no contact with the 5th infraorbital. The infraorbitals are well-developed but the 4th does notcover the entire cheek and the 5th is reduced to a thin ossification around the sensory canal tube(Fig. 12A). Comments and comparisons A reduced supraorbital is present in Securicula (Fig. 12B), Oxygaster (Fig. 13), Salmostoma (Fig. 12C) and Aspidoparia, but in Chela and Rasbora it is wide (Fig. 12D). In Culler, Erythroculter 158 G. J. HOWES and most other cultrine genera the supraorbital is moderately developed. In Pelecus as in Macro-chirichthys, the supraorbital is small, but unlike Macrochirichthys, the bone in Pelecus is expandedanteriorly and is in contact with the lateral ethmoid. SOR B Fig. 12 Circumorbital series of A. Macrochirichthys macrochirus, B. Securicula gora, C. Salmostoma bacaila, D. Chela laubuca. The infraorbitals of various cyprinids have been discussed at some length in an earlier paper(Howes, 1978) where it was noted that the 4th and 5th infraorbitals in many genera are reducedand that there is no contact between the 5th infraorbital and the supraorbital. In Securicula allthe infraorbitals are well-developed, the 4th almost covering the cheek and the 5th also expanded(Fig. 12B). A similar degree of development is found in Salmostoma, Aspidoparia, Chela andRasbora (Figs 12C & D). In Oxygaster the ossification of the 4th and 5th bones is reduced toalmost the canal and the 5th contacts the supraorbital (Fig. 13). The canal running through thefirst infraorbital (lachrymal) is usually branched in most cyprinids, but in all the genera notedabove (including Macrochirichthys) it is a straight unbranched tube. I nt IT muscular bones and the body musculature (Figs 14-18) The anterior intermuscular bones of Macrochirichthys are strongly developed. Five bonesarticulate with the posterior edge of the epioccipital, just medial to the pterotic (Fig. 14). All arealmost equally developed needle-like elements whose distal surface bears a slight lamellar ridge. THE ANATOMY OF MACROCHIRICHTHYS MACROCHIRUS 159 Fig. 13 Circumorbital series of Parachela oxygastroides. The points of the bones extend to between the eleventh and fourteenth vertebrae. In a largespecimen (212 mm SL) the bones are closely united anteriorly, one above the other, so as toform a laminated beam (Figs 14 & 15). Below this beam and running parallel to it, are anotherfour or five intermuscular bones (LIM, Figs 15-18) but these have no connection with thecranium. The epaxialis muscle can be regarded as being in two parts; an upper section (Depx, Figs 15-18)which reaches to the anterior part of the cranium, and a lower section (Vepx, Figs 16-18) lyingmedial to the intermuscular bone beam. In fact the two sections are merged and it is only thestratified nature of the lower part that enables such a division to be made (see below). In the dorsal section of the epaxialis the fibres are long and are directed forward at an angle of5 to the horizontal plane, and transversely at 3-5 to the medial plane. There are no distinctmyomeres, their boundaries are indicated laterally by cord-like myosepta (Ms, Fig. 15) angledat 5 to the horizontal. Medially the 'myosepta' become tendinous bands which permeate theepaxialis. Anteriorly, a tendinous septum extends from the second neural plate and the neuralcomplex (Ets, Fig. 16) to insert along the low supraoccipital crest. EPO CIM1 CIM4 3mm Fig. 14 Cranial intermuscular bones of A. Securicula gora, B. Macrochirichthys macrochirus seen in dorsal view. 160 G. J. HOWES CO O THE ANATOMY OF MACROCHIRICHTHYS MACROCHIRUS Sea 161 CIM Vepx Tsca Hlms Ets Depx LIM Obi Fig. 16 Macrochirichthys macrochirus. Dorsal body musculature. Oblique dorso-lateral view, semi-diagrammatic. The epaxial musculature has been cut away ; exposed parts of the skull and vertebralcolumn are shaded. The connection between the lower part of the epaxialis and the cranial intermuscular bonebeam is a complex one and is shown semi-diagrammatically in Figs 17 & 18. The bones areconnected to one another by an outer layer of widely spaced bands of muscle fibres orientatedat angles of 40 to the horizontal (Lepx, Figs 15-18). Extending mesad from each bone is a thinhorizontal myoseptum which separates layers of muscle fibres. In the top layer the fibres aredirected toward the medial plane at the same angle as those in the overlying dorsal part of theepaxialis. Indeed, as mentioned above, the fibres of the two sections become merged and there isonly a marginal myoseptum extending inward from the upper intermuscular bone. In each lowerlayer the fibres become more obliquely angled toward the medial plane, until those in the bottomlayer strike the medial plane at 30-35 (Fig. 18). Thus, in a vertical section, the fibre arrangementis seen to follow a helical trajectory. Anteriorly, all the layers converge and terminate intotendinous bands which insert at the point of articulation of the intermuscular bone beam and thecranium. The posterior tips of the cranial intermuscular bones are connected to the apices of thosemyomeres which form the posterior part of the epaxialis. The supracarinalis anterior (Sea. Figs 16-18) originates from the first dorsal pterygiophoreand extends forward as a broad band, triangular in cross-section, to a point above the neuralcomplex. From there the muscle inserts into a thick tendon which at first runs dorsally to, andthen eventually joins the midline septum (Ets, Fig. 16). 162 G. J. HOWES The lateralis superficialis muscle (Ls, Figs 15-18) is composed of three narrow bands of only afew fibres thickness. The medial surface of the lateralis is closely applied to the underlyinghypaxialis and appears to be interlaced with fibres of that muscle. Anteriorly, the lateralis insertsvia a thick tendon on to the upper part of the cleithrum. The hypaxialis musculature is clearly divisible anteriorly as the obliquus superiorly (Obs, Figs 1 5,16 & 18) and the underlying obliquus inferioris (Obi, Figs 15, 16 & 18). The fibres of the o.superioris are directed at angles of 27-30 to the horizontal. Medially, insertion is by way ofshort segments (Hms, Fig. 17) plugging into the lower cavities of the centra. These segments arebordered ventrally by a broad tendon which extends between the posterior edge of the rib and itsrespective centra. Anteriorly, the fibres of the o. superioris insert via a thick tendon on to theupper part of the cleithrum, just below the insertion point of the lateralis superficialis. The fibre direction of the anterior part of the o. inferioris varies from a 20 downward slopedorsally to a 10 upward slope ventrally. That part of the muscle running along the ventralmargin of the body consists of rather widely spaced bands of tendinous fibres; the ventral edge, orkeel, is a transluscent band of highly elastic connective tissue. Beyond the pelvic fins the epaxialis and hypaxialis merge to form the typical teleostean patternof zig-zag myomeres. Comments and comparisons Cranial intermuscular bones are developed to a greater or lesser degree in many cyprinids but areparticularly well-developed in those genera with compressed, generally elongate bodies andobliquely aligned crania (see p. 171). Genera included in this category are : Securicula, Salmostoma,Chela, Pseudolaubuca, Paralaubuca, Oxygaster and Pelecus. In none of these, however, is thereanything like the degree of cranial intermuscular bone (and associated epaxial muscle) develop-ment found in Macrochirichthys. In Securicula there are four or five bones articulating with the posterior face of the cranium,but unlike the situation in Macrochirichthys they do not all articulate directly with the craniumbut are attached to the epioccipital and supraoccipital by ligaments (Fig. 14A). Only the outerbone articulates with the epioccipital. A similar arrangement is found in other genera cited above,where again only the upper bone is firmly united to the cranium. In Salmostoma the cranial intermuscular bones are weakly developed but tendinous bundlesof the epaxialis run onto the epioccipital. No doubt ossification of these tendons has given riseto the situation found in Macrochirichthys. With one exception all the genera noted above have short and markedly divergent cranialintermuscular bones unlike the horizontal bundles in Macrochirichthys. The exception is Securi-cula where the bones are long and diverge little from each other, approximating to the conditionfound in Macrochirichthys. The functional significance of the cranial intermuscular bones, and the organization of theepaxialis is discussed on page 182. Vertebral column (Figs 19-26) The vertebral column in Macrochirichthys presents many interesting specializations. Not all thecentra lie in the same horizontal plane, the dorsal surfaces of the 5th and 6th centra marking thehighest point of the vertebral column. The 4th centrum is markedly sloped and serves as a 'step'to connect the lower level of the first three centra to the higher of the succeeding elements. Fromthe 7th vertebra, the column slopes gently downward to the 18th or 19th centra where the axisis in the same horizontal plane as that of the first three centra (Fig. 19). There are a total of 49-50 vertebrae (27 or 28 abdominal + 22 or 23 caudal excluding the fusedPUi + Ui elements); in one specimen there is a fusion of the 23rd, 24th and 25th centra. The first vertebra (VI, Figs 20A-C) is small and ovoid in transverse section with a convexanterior face which articulates with the basioccipital socket. Short lateral processes are present onthe upper part of the centrum. Antero-ventrally two small projections rest upon the anteriorlydirected arms of the 2nd vertebra (see below). A pad of cartilage lies between each projectionand its respective supporting arm. THE ANATOMY OF MACROCHIRICHTHYS MACROCHIRUS .Depx 163 Vepx Hms Hypx Fig. 17 Macrochirichthys macrochirus. Anterior oblique view of a transverse section through thedorsal body musculature. The section is taken at a point near the 8th vertebra. Skeletal elementsare shaded. Sea Depx Obs Fig. 18 Macrochirichthys macrochirus. Posterior oblique view of a transverse section through thebody musculature. The axis of the vertebral column is indicated by x . The horizontal myoseptaof the ventral epaxial muscle are indicated by dashed lines. The angles made by the fibres with themedian vertical plane are shown for each segment. The thick black lines represent the cranialintermuscular bones. 164 G. J. HOWES OID O oc II I II B 9\ O ~ -C 8i * - THE ANATOMY OF MACROCH1RICHTHYS MACROCHIRUS 165 The 2nd vertebra is elongate, shaped anteriorly like the seat of an armchair (V2, Figs 20A-C).The seat itself is formed by two diverging arms, upon which rest the ventral projections of the 1stvertebra (see above). The centrum bears deep lateral processes, the anterior faces of which areslightly concave and articulate along their distal margins with the upper part of the cleithrum(see p. 177). Dorso-posteriorly each process extends caudad a thick spine. The 3rd vertebra (V3, Fig. 2 IB) is not fused with the 2nd and laterally carries the fossa inwhich the tripus articulates. B LP2 VC1 Fig. 20 Macrochirichthys macrochirus, 1st and 2nd vertebrae. A. Dorsal, B. Ventral and C. Lateral views. The 4th vertebra (V4, Fig 2 IB) bears lateral processes and the ossa suspensoria. The ventralsurface of the centrum slopes upwards thus bringing its posterior face to the same level as the5th and 6th centra which lie in a higher horizontal plane (see above). The second neural plate (NP2, Fig. 21B) overlies the 1st and 2nd vertebrae. It is widely separatedfrom the cranium. On either side, below its anterior border, lie the claustra, each of which articu-lates with the bowl of the ladle-shaped scaphia ; in turn the stems of the scaphia articulate with theleading edge of the third neural plate (NP3, Fig. 2 IB). This large, broadly triangular bone coversthe dorsal border of the 3rd centrum and overlies, but does not contact, the posterior half of the2nd centrum. Extending from the posterior border of the third neural plate is the neural complex(NC, Fig. 2 IB) which is directed caudad at an angle of 20 to the vertebral column. Its posteriortip almost contacts a horizontally aligned supraneural. Basally the neural spine of the 4th vertebracontacts the neural complex, but halfway along its length is separated from this element. Distallyit articulates with a fork of the first supraneural (SN1, Fig. 21B). The neural spine of the 5th vertebra articulates distally with the anterior fork of the secondsupraneural (SN2, Fig. 2 IB). This supraneural extends horizontally over the sixth neural spineto contact the next rod-shaped supraneural lying between the sixth and seventh spines. Fromthis point backwards a supraneural lies between each successive neural spine. However, thedorsal border of each supraneural becomes progressively less elongate until the bones have theform of a compressed nail (Fig. 19). 166 G. J. HOWES C/3S _f C/3 e E I fS - THE ANATOMY OF MACROCHIRICHTHYS MACROCHIRUS 167 When the anterior elements of the vertebral column of the adult Macrochirichthys are comparedwith those of the juvenile, several differences are apparent. In a juvenile of 30 mm SL the neural complex is a small triangular structure overlying the 1stand 2nd vertebrae (Fig. 21 A). This is, in fact, the morphology of the second neural complex foundin adults of other genera examined. The neural complex appears to be composed of two fusedelements and is clearly separated from the fourth neural spine which is expanded distally as alamellar plate. The 1st and 2nd vertebrae also differ from their adult condition. The 1st vertebrabears prominent forwardly directed lateral processes; similar but larger processes are alsopresent on the 2nd vertebra (Fig. 22). It would appear that the processes of the 2nd vertebra growforward and those of the 1st vertebra grow downward so that the 'cradle' of the adult is formed(see below). 3mm Fig. 22 Macrochirichthys macrochirus, 1st and 2nd vertebrae of a specimen 30 mm SL. A. Dorsal and B. Lateral view. The sequence of changes that lead from the juvenile to the adult form are apparently as follows:the 2nd vertebra elongates, developing lateral and ventral processes; the anterior dorsal marginof the 3rd centrum grows forward to contact the first neural plate which, in turn, contacts anddevelops along the anterior border of the neural complex. The fourth neural spine expandsanteriorly to unite with the posterior border of the neural complex; distally, the expandedportion of the fourth neural spine separates to become a supraneural which then grows forwardto contact the neural complex. Comments and comparisons In an earlier paper (Howes, 1976) I drew attention to the peculiar arrangement of the dorsalelements in the vertebral column of Macrochirichthys. However, in figure 25 of that paper twoanterior elements, comprising the neural complex, are mislabelled as neural spines, and the extentof the first vertebra is incorrectly indicated. I also remarked that the whole series of neuralarches and supraneural elements forms an arc-like septum possibly serving to counteract stressesimposed by a presumed backward and upward movement of the cranium. It is now apparentthat such a movement of the skull does occur (see p. 182) and that the type of articulation betweenthe basioccipital and the first vertebra, coupled with the modifications to the 1st and 2nd vertebrae,serve to indicate the degree of movement possible (see p. 183). Like Macrochirichthys the first centrum of Securicula, Salmostoma, Oxygaster and Chela istapered anteriorly and presents a convex face articulating with the basioccipital (Figs 23A-C).Although in Pelecus the 1st vertebra has a rounded anterior face, it is not tapered. In othercyprinids the anterior face of the 1st centrum is flat or concave, a disc of cartilage being interposed 168 G. J. HOWES between it and the basioccipital. All the genera mentioned above have a 1st vertebra with distallyexpanded lateral processes. In none has the 1st vertebra been modified to the extent it has inMacrochirichthys, but in some Oxygaster species there is a marked anterior extension of thelateral processes which thus resemble the condition found in the 2nd vertebra of the juvenileMacrochirichthys (Fig. 22 and p. 167). The lateral processes of the first vertebrae in Securicula,and Salmostoma are directed laterally but in Chela laubuca, although there is a pronouncedlateral expansion of each process, the posterior border is curved and directed caudad to underlie B Fig. 23 1 st and 2nd vertebrae of A. Parachela oxygastroides (dorsal view). B. Securicula gora (ventralview). C. Chela laubuca (ventral view). In Securicula the 2nd and 3rd centra are fused. the lateral process of the second vertebra. In Chela maasi and C. caeruleostigmata the distalmargin of the lateral process of the first vertebra is considerably extended caudad; it is alsoclosely united with the process of the 2nd vertebra to form a wide flange. The broad anterioredge of the first lateral process pivots against transverse expansions of the upper part of thecleithruin (see p. 183). (The information on these two species has been provided by Dr C. C.Lindsey.) The 2nd and 3rd vertebrae are separated in Chela, Oxygaster and Salmostoma just as they arein Macrochirichthys, but in Securicula they are fused (Fig. 23B). Although fusion of the secondand third elements appears to be the general condition in the cyprinids, there are genera, otherthan those mentioned above, in which they are separated (e.g. Opsariichthys, Hemiculterella,Alburnus}. Whether this separation is indicative of a plesiomorph condition as suggested byGreenwood et al. (1966) can only be determined when relationships of these two centra areknown for more genera. It does not appear to be of functional significance as is testified by itspresence in Macrochirichthys and absence in Securicula and Pelecus which are almost all exactlyalike in their gross cranial morphology. THE ANATOMY OF MACROCHIR1CHTHYS MACROCHIRUS 169 The neural complex in Securicula, Oxygaster and Salmostoma has basically the same morph-ology as that described for Macrochirichthys. In Securicula it is directed caudad at almost the same angle as in Macrochirichthys (30) and isfused basally to the neural spine of the fourth vertebra (Fig. 24A). Distally, the fourth neuralspine is expanded and contacts the neural complex; posteriorly its tip is forked and articulateswith a supraneural The supraneurals are small, vertically aligned bones lying between eachneural spine (Fig. 23). NS4 NP2 3 mm SN1 NC NP3 3mm Fig. 24 Anterior vertebral column of A. Securicula gora, B. Chela laubuca. Most species of Oxygaster display a similar arrangement between the neural complex and thesupraneurals. As in Macrochirichthys the first two supraneurals are rod-like structures lyingalmost horizontally. However, in Oxygaster anomalura the anterior supraneurals are wide laminarbones and the neural complex does not contact the neural spine of the 4th vertebra as it does inits congeners (see p. 189 and Fig. 26B). Salmostoma strongly resembles Oxygaster anomalura in the development of the supraneuralsand in the angle at which the neural complex lies to the vertebral column (30 cf. 35 in O.anomalura; 40-45 in other Oxygaster species). The neural complex of Salmostoma is larger thanin any of the genera previously mentioned. In Chela there is a complex locking arrangement between the anterior supraneurals, none ofwhich contacts the neural spines (Fig. 24B). The fourth neural spine does not contact the neuralcomplex and is separated from it by the enlarged third neural plate (Fig. 24B). 170 G. J. HOWES SN1 NC NP3 Fig. 25 Anterior vertebral column of A. Pseudolaubuca sinensis (2nd & 3rd centra separatedventrally but fused dorsally). B. Pelecus cultratus (2nd & 3rd centra fused). C. Alburnus alburnus(2nd & 3rd centra entirely separated). Other genera currently assigned to the Cultrinae also possess hypertrophied supraneuralssome of which articulate with neural spines. This arrangement is particularly well-developed inPseudolaubuca where the supraneurals form a strong dorsal septum (Fig. 25A). A similar situa-tion, but one developed to a lesser degree, is found in Pelecus (Fig. 25 B) and Paralaubuca. As mentioned above (p. 167), it appears that this arrangement of supraneurals and closelyassociated neural spines serves to combat stresses generated by the elastic movements of themyosepta extending between them. (See also p. 182). In Macrochirichthys, Securicula, Salmostoma, Oxygaster, Chela, Rasbora and Pelecus theposterior face of the cranium is acutely inclined, and the supraoccipital process reduced or THE ANATOMY OF MACROCHIRICHTHYS MACROCHIRUS 171 truncated. There is thus a wide space between the rear of the skull and the neural complex. Thisspace is occupied by epaxial muscle and connective tissue (Fig. 26). Most other cyprinid genera have a vertically aligned neural complex, most often extendingforward so as to contact (e.g. Labeo, see Howes, 1978), or almost contact, the supraoccipitalprocess. D Fig. 26 Crania and anterior vertebral elements of A. Salmostoma bacaila. B. Oxygaster anomalura,C. Parachela oxygastroides, D. Chela laubuca. Supraoccipital process hatched, 1st supraneuralshown in black. All drawn to same scale. The angle at which the cranium is aligned to the vertebral column is undoubtedly of greatadaptive significance in cyprinids. A shift in angle results in an equivalent reorientation of thejaws, which in the case of Macrochirichthys means that the jaws are almost vertical when themouth is closed. In this fish the parasphenoid lies at an angle of 20 to the vertebral column andthe posterior part of the cranial roof slopes backward at 10. The same angles are measured inSecuricula and Pelecus; as in Macrochirichthys, it is only the posterior (post-parietal) part of thecranium that slopes, anteriorly it is almost horizontal. The same angles are again found inOxygaster anomalura but here the cranial roof has a continuous slope broken only by the raisedparietal ridges (see p. 172 and Fig. 26B). Other Oxygaster species have the parasphenoid alignedat an angle of 20-25 (the same as the anterior part of the cranial roof, Fig. 26C). The para-sphenoid in Salmostoma lies at 20 to the vertebral column and the cranial roof at 25; as inMacrochirichthys and Securicula it is only the post-parietal part of the cranium that is sloped(Fig. 26A). The dorsal profile of the cranium in Chela is convex, with a marked posterior slope, thesupraoccipital being confined entirely to the posterior part of the skull. The parasphenoid liesat 20 to the vertebral column, an angle no greater than in the other genera considered; but theepaxial musculature makes an oblique angle with the cranium whereas in the other examples it 172 G. J. HOWES lies almost horizontally. Apart, that is, from those Oxygaster species in which the musculaturehas extended to the anterior part of the skull (Fig. 26D). Mention was made above of the parietal ridges in Oxygaster anomalura and of the differencebetween this and other Oxygaster species in the angle formed between the cranial roof and thevertebral column. Only a slight change in this orientation would enable the epaxial musculatureto extend further forward, with a consequent reduction and finally a complete disappearance ofthe parietal ridge. This may well have been the transformation sequence from the ancestralform to the derived species of Oxygaster (see p. 189). B PMX MX Fig. 27 Macrochirichthys macrochirus jaw bones. A. Lower jaw. B. Anterior dentary of a specimen 30 mm SL. C. Upper jaw. Lateral views. Jaws (Figs 27-29) The premaxillae of Macrochirichthys are long thin bones with short triangular ascending processes (Fig. 27C). Each ascending process curves mesad to meet its fellow along the midline; contact is effected by a socket joint, the faces of one side being raised to fit into an elongate groove in the face of the other (Fig. 28). The separation of the ventral leading edges of the premaxillae by this type of joint enables the prominent tip of the lower jaw to be accommodated when the mouth is closed. The maxilla is expanded anteriorly. Its ventral border is rounded and overlaps the premaxillafor half of that bone's length; beyond this point it lies along the top of the premaxilla. Anteriorly,the ventral medial process, which overlaps the inner side of the premaxilla, widens and is linkedwith its partner by a thick ligament. The dentary (Fig. 27A) is shallow, its anterior tip produced into a high, mallet-like process.Lying posterior to this process is a deep notch. In a juvenile specimen (30 mm SL) the symphysialprocess is produced ventrally as well as dorsally and there are two shallow notches (Fig. 27B).The coronoid process of the lower jaw is shallow and is formed partly from the dentary andpartly from the anguloarticular. The posterior margin of the coronoid process (anguloarticular)is bent outward as a narrow flange and provides an insertion area for the tendon of adductormandibulae A 2 muscle. Comments and comparisons When the mouth of Macrochirichthys is closed the kinethmoid lies in the anterior cavity of the THE ANATOMY OF MACROCHIRICHTHYS MACROCHIRUS 173 ethmoid block, and the symphysial process of the lower jaw lies between the premaxillaries. Asthe lower jaw moves downward, protrusion of the upper jaw is effected by the forward rotationof the kinethmoid pushing the premaxillaries forward (Fig. 29). The marked upper jaw protrusion seen in most other cyprinids (Alexander, 1966) is lost inMacrochirichthys, because of the direct connection between the kinethmoid and the premaxil-laries. In the majority of cyprinid genera the kinethmoid is connected to the premaxillaries by along ligament which enables the necessary protrusion. PMX 3mm Fig. 28 Macrochirichthys macrochirus, dorsal view of upper jaws. The jaws of Securicula are shorter than those of Macrochirichthys but the dentary is deeper andthe coronoid process is not set so far posteriorly; the process is formed entirely from the dentary,the anguloarticular meeting it at a shallow angle and presenting a long dorsal border. Thesymphysial process, however, is well-developed and is followed by a pronounced cavity in theupper margin of the dentary. Salmostoma has an almost identical jaw morphology. Only Oxygaster has the same kind of premaxillary socket joint as Macrochirichthys (see p. 185). Various types of cyprinid jaw have been discussed in an earlier paper (Howes, 1978) where itwas suggested that those species with elongate jaws lack the degree of protrusibility of the shorterjawed species, a condition exemplified by Macrochirichthys. In Chela the upper jaw is protractile, although not to the degree seen in some barbine orleuciscine genera; the lower jaw is shallow and widely curved mesad. The gape is large and whenopened the mouth is almost circular. The functional significance of this type of mouth is con-sidered on p. 184. Suspensorium and associated musculature (Figs 30-32) The hyomandibula of Macrochirichthys has a wide lateral face which bears a large fossa, theventral border of which projects anteriorly as a small laminar process (HMP, Fig. 30A). Thiscavity provides the site of attachment for the levator arcus palatini muscle. A description of thismuscle was given in a previous paper (Howes, 1976 : 242, fig. 24) where it was noted that theelement is divided, the outer part inserting onto the small lateral process. The lower limb of thehyomandibula is directed forward at an angle of 45 from the vertical. 174 G. J. HOWES The metapterygoid and entopterygoid are extensive bones (Fig 30A). The metapterygoid joins,and slightly overlaps, the limb of the hyomandibula. Its lateral face provides a site for theattachment of the small adductor areas palatini muscle. A fibrous sheet of connective tissueextends from the palatine to the lateral faces of the metapterygoid and entopterygoid (see fig. 23 inHowes, 1976). LKE KE PMX 3mm Fig. 29 Macrochirichthys macrochirus, ethmoid-jaw connection. Dorso-lateral view. The ectopterygoid is long and narrow and has a wide union with the palatine. The autopalatineitself is thick and has a long medial process articulating with the ethmoid. The quadrate contains a small foramen situated just posterior to the articular condyle (QF,Fig. 30A). The quadrate together with the metapterygoid and symplectic border a fenestra in the suspen-sorium (MQF, Fig. 30A). Comments and comparisons The only other genus presently included in the Cultrinae which has a lateral process on thehyomandibula is Pseudolaubuca. In this case it serves the same function as the process in Macro-chirichthys, namely, as an insertion point for a d'vided levator arcus palatini muscle. In Securiculathe hyomandibula is narrower than that of Macrochirichthys and the ventral limb is verticallyaligned (Fig. 30B). There is only a slight indication of a lateral depression. The metapterygoidjoins the hyomandibula halfway along the ventral limb of the later, which it overlaps laterally.The levator arcus palatini is divided in Macrochirichthys, but the inner section of the muscleinserts on the hyomandibula and the outer on the metapterygoid (Figs 31 A & B). The suspensorialfenestra is larger than in Macrochirichthys and the dorsal edge of the symplectic provides theentire lower border of the fenestra. There is a large quadrate foramen present (Fig. 30B). The metapterygoid-quadrate fenestra has been commented upon and its functional significancediscussed in Macrochirichthys in an earlier paper (Howes, 1978). It may be added here that inaddition to Opsariichthys, Zacco and Macrochirichthys this fenestra is also recorded in Securicula THE ANATOMY OF MACROCHIRICHTHYS MACROCHIRUS HMP 175 PAL B 3mm Fig. 30 Hyopalatine arch in lateral view of A. Macrochirichthys macrochirus, B. Securicula gora. (=Pseudoxygaster), Salmostoma (Mirza, Alam & Kausar, 1974), Aspidoparia (p. 192) andLuciosoma (pers. obs.). When comparing the various Salmostoma species one encounters asituation like that existing between Macrochirichthys and Securicula, namely that with a lengthen-ing and near vertical orientation of the jaws there is a reduction in size of the fenestra and areduction in length but deepening of the symplectic (cf. Salmostoma sardinella - a short-jawed Lap1 A B Fig. 31 Securicula gora, levator arcus palatini muscle. A. Outer aspect. B. Inner layer. 176 G. J. HOWESMET EOT ECT Fig. 32 Pterygoid bones of A. Salmostoma sardinella, B. Salmostoma bacaila. C. Aspidoparia mora.Metapterygoid-quadrate fenestra hatched. All drawn to same scale. COR B CL 5mm 3mm Fig. 33 Pectoral girdles in lateral view of A. Macrochirichthys macrochirus, B. Securicula gora. THE ANATOMY OF MACROCHIRICHTHYS MACROCHIRUS 177 species, and S. baicala - a long-jawed species, Figs 32A-C). It is interesting to note that inAspidoparia, although the fenestra is greatly reduced, it appears to be the result of a partiallyreversed trend, i.e. a shortening of the lower jaw combined with its near vertical orientation(Fig. 32C). Along with earlier authors I had considered this fenestra as a plesiomorph characterfor the cyprinids (Howes, 1978), an assumption which I think is borne out by the condition of thisfeature in Salmostoma, a taxon I have reason to believe is the plesiomorph member of the groupunder discussion (see p. 186). PTT B 1mm Fig. 34 Macrochirichthys macrochirus, supracleithrum, posttemporal and extrascapular. A. Adult, B. Juvenile (30 mm SL). Pectoral girdle and associated cranial bones (Figs 33-36) The upper limb of the cleithrum in Macrochirichthys is short and columnar, sloping forward atan angle of 45 to the vertical. The upper part of the medial face bears a narrow process which isattached by a thick ligament to the anterior face of the transverse process of the 2nd vertebra(see p. 165). The lower cleithral limb slopes anteriorly at 45 from the vertebral axis. This lowerpart is long and its anterior tip comes to lie below the posterior part of the orbit (Fig. 33A). The coracoids are extensive and contact each other along their medial faces. The posterior borderof each coracoid is markedly concave and the ventral border extends backwards to a point belowthe pectoral fin. The supracleithrum (SC, Fig. 34) is a broad, triangular bone, its anterior dorsal border curvedlaterally to overlie the edge of the posttemporal. The sensory canal runs along the middle of thesupracleithral face. The posttemporal is cleaver-shaped, its posterior border rounded, the sensorycanal running close to its lower border (PT, Figs 34A & B). Along the antero-ventral border ofthe posttemporal lies the extrascapular which may sometimes be fragmented into two elements(ES, Figs 34A & B). In a juvenile specimen (30 mm SL) the supracleithrum is a squared S-shaped bone with a well-developed dorso-lateral flange; the posttemporal has a more rounded posterior border and theextrascapular is in contact with the ventral border of the posttemporal (Fig. 34B). The postcleithrum of the adult is extremely long and is curved ventromesially, its dorsal tiplying at the same level as the posteroventral tip of the coracoid (Fig. 33A). 178 G. J. HOWES SCL SCL PCP CCF Fig. 35 Pectoral girdles of A. Salmostoma bacaila, B. Oxygaster anomalura, C. Parachela oxygas-troides, D. Pelecus cultratus, E. Chela laubuca in lateral and F. Dorsal view. Comments and comparisons Large pectoral fins with a correlated expansion of the coracoids appear to be characters sharedby many genera currently assigned to the Cultrinae. However, the morphology of the pectoralgirdle differs significantly amongst these genera. The short, anteriorly inclined upright limb of thecleithrum in Macrochirichthys and Securicula is columnar (Figs 33A & B), whereas in Oxygaster,Salmostoma and Chela it is lamellar (Figs 35A, B, C & D). In other cultrine genera (apart fromPelecus; see below) the limb is long and vertically aligned, and the lamellar border is extendedposteriorly, a condition typical for the majority of cyprinids. In Pelecus, although the uprightpart of the cleithrum is short and slopes forward, it is broadly lamellar and the supracleithrumarticulates halfway along its length instead of ioining the cleithrum at its dorsal point as it does inMacrochirichthys and the other genera cited above (Fig 35 D). The supracleithrum in Oxygaster is broad, and in O. anomalura has a slight lateral lip overlyingthe depression in which the posttemporal articulates (Fig. 36A). The posttemporal in this species iselongate and has the same shape as that of Macrochirichthys, whereas in other species of Oxygasterthe bone is short and curved sharply forward. In all species of Oxygaster the sensory canal runs THE ANATOMY OF MACROCHIRICHTHYS MACROCHIRUS 179 close to the posterior border of the bone. The extrascapular of O. anomalura is elongate with anupwardly curved anterior tip, and again it more closely resembles its counterpart in Macro-chirichthys than that of the other Oxygaster species. The supracleithrum in Salmostoma is narrowly triangular, the sensory canal running alongthe middle; the posttemporal is wide and lacks an indented ventral border. The extrascapular toois triangular and partly overlies the anterior margin of the posttemporal (Fig. 36D). Althoughthe supracleithrum and posttemporal in Securicula are wider and shorter than those of Salmos-toma they share the same characteristics and likewise the extrascapular lies at the centre andoverlaps the anterior border of the posttemporal (Fig. 36C). Fig. 36 3mm Supracleithrum, posttemporal and extrascapular in A. Oxygaster anomalura. B. Parachelaoxygastroides. C. Securicula gora. D. Salmostoma sardinella. E. Chela laubuca. In Chela the supracleithrum is extensive, its anterior border extending downward to almost thelower part of the cleithrum (Figs 35E & 34E). The shape of the posttemporal and of the extra-scapular more nearly resembles Oxygaster anomalura than any other taxon. A notable featureof the pectoral girdle of Chela is the medial extension of the upper part of the cleithrum. Thispart of the cleithrum contacts the leading edge of the transverse process of the first vertebra,similar to the situation in Macrochirichthys (see above). In Chela maassi the medial cleithralextensions are most extensive and appear to act as part of a pivot for the cranium against thevertebral column (information supplied by Dr C. C. Lindsey; see also p. 184). The coracoidsare not greatly extended and are widely divergent. There is much variation in the degree of development of the coracoids, which are most extensivein Macrochirichthys, Securicula and Pelecus. In Securicula as in Macrochirichthys the medialfaces of the coracoids are in contact over most of their length but lack the posteroventral extensionfound in that genus; in this respect, but not in their greater depth, they more closely resemble 180 G. J. HOWES the coracoids of Salmostoma (cf. Figs 33B & 35A). A prolongation of the posterior coracoidborder is present in all Oxygaster species but in this genus it takes the form of a midlateral ratherthan a posteroventral extension. In Pelecus the coracoid border is concave, and in other cultrinesit is straight or rounded. The ventral coracoid border is deeply incised in all Oxygaster speciesbeing most marked in O. hypophthalmus, and weakest in O. anomalura (Figs 35B & C). A weaklyincised border is also found in the coracoid of Securicula (Fig. 33B), and there is some indentationin a juvenile Macrochirichthys (30 mm SL) but no sign of this exists in any adult specimens I haveexamined. Sorescu (1968) notes and figures an incised coracoid in Macrochirichthys; unfortunatelyshe did not state the size of the specimen examined. An incised coracoid is present in Pelecus (noted and figured by Rauther, 1950 and Sorescu,1968). Here, however, the indentations are narrow and finger-like, thus quite unlike the widealmost triangular or ellipsoidal indentations of the genera cited above (Fig. 35D). The only other cyprinid in which I have found an irregularity of the coracoid ventral border isAlburnus, in which it is serrated. An indented coracoid possibly has some functional association with the way in which thepectoral fins are extended and rapidly jerked forwards (see p. 183). In passing it may be notedthat in some characoids which have extensive coracoids (Gasteropelecus, Thoracocharax), thebones bear deep grooves which provide attachment for tendons supporting bundles of theadductores superficial muscle. In the cyprinids the indentations are covered by a tendinous fasciaand in both cases the channeling of the coracoids possibly provides a reduction in weight, anincreased area for muscle attachment (in the characoids), and possibly a shock-absorbent system(in the cyprinids). In all other genera placed in the Cultrinae the coracoids are not in contact along their medialfaces, and diverge from one another to varying extents; all have a large fenestra between thecoracoid and the cleithrum (anterior fenestra of Brousseau, 1976). In Chela the anterior fenestrais reduced in size or may be completely absent (Fig. 35E). Although a fenestra is present inRasbora it shows considerable interspecific variation in size, in some species being reduced to aminute opening and in others confined to the coracoid. A similar situation occurs in Danio.As in Rasbora the anterior fenestra is absent , but the foramen is developed in the high anteriorcrest of the medial dorsal ridge of the cleithrum (ventral cleithral lamina of Brousseau, 1976). Mesially curved, elongate postcleithra, like those of Macrochirichthys are found in all Oxygasterspecies. Postcleithra are absent in Securicula and are reduced to short straight bones in Salmos-toma. In other cultrines the postcleithra vary from being long and curved in Culler and Erythro-culter (although never forming a wide arc as in Oxygaster and Macrochirichthys) to short andstraight in Pelecus. The abdominal keel and scale rows (Figs 37 & 38). The ventral surface of the abdomen of Macrochirichthys is greatly compressed, with a knife-likeedge. The scales do not overlap along the ventral midline, with the result that the skin is exposedmedially below the lowest row of scales. The exposed skin is translucent and pervaded byoblique strands of tendinous tissue. Above and around the pectoral fin origin the skin is loose and the scale rows broadly overlap.When the pectoral fins are moved downwards and rotated forward the skin is taught and thescale rows become vertically aligned with hardly any overlap (Figs 37A & B). There is no pectoralaxial scale. Comments and comparisons The presence of a ventral keel has been a major diagnostic feature in defining the subfamilyCultrinae and the extent to which it is developed has been used in delimiting certain cultrinegenera (see, for example, pages 194-195). Most cyprinid fishes with laterally compressed bodies have the abdomen keeled along themidline (e.g. Nematabramis, Chelaethiops), the keel being formed by overlapping of the scalerows. The sharpness of the keel varies, and its longitudinal extent is often difficult to determine.Specimens of various cultrines I have examined show that the development of the keel varies THE ANATOMY OF MACROCHIRICHTHYS MACROCHIRUS 181 Fig. 37 Macrochirichthys macrochirus. Outline drawings of head, pectoral fin and associated scalesin A. normal position, B. with head elevated. Note forward rotation of first pectoral fin ray,expansion of scale rows and ventral curvature of the abdomen. Drawings made from preservedspecimens. intraspecifically and is dependent upon the depth of the body, the degree of lateral compressionand the condition of preservation of the specimens. It is, therefore, a character of limited value fordefining genera. A prominent axillary scale is situated behind the pectoral fin in both Salmostoma and Securicula;in Securicula it is developed as an elongate structure and is thickened along its lower border(Fig. 38). I have not found a scale of this type in any other cultrine genus, although in some asmall, fleshy axial lobe may be present. Elongate axial scales are, however, present in some speciesof Chelaethiops and Barilius where they appear to be correlated with the extension of the pectoralfins. However, this correlation is not always evident as for example in Leptocypris where thepectoral fins are relatively short but the axial scale is between 50 and 75 % their length. If thedevelopment of the scale is related to the size of the pectoral fin then one would have expectedsuch a structure to be not only present but well-developed in Macrochirichthys. It may well be thatin those taxa where it occurs it has a hydrodynamic function, perhaps as a fairing to reduceturbulence. Whatever function it may have, the axial scale is considered to be a derived character. Discussion From the observations presented here and from a previous description (Howes, 1976) severalcomments can now be made concerning the anatomy and phylogenetic relationships of Macro-chirichthys. 182 G. J. HOWES Functional morphology Earlier (Howes, 1976) I noted that certain, features of the vertebral column of Macrochirichthyswere indicative of some elevation of the skull. Confirmation of this type of mobility comes fromobservations made on aquarium specimens (pers. obs. and information provided by K. Purbrickand D. Bird) and freshly caught specimens (information provided by Dr T. R. Roberts). The elevation of the cranium would seem to depend on two coordinated systems; (1) themovements of the upper section of the epaxialis muscle and its associated tendons, and (2) therotation of the pectoral girdle. 3mm Fig. 38 Securicula gora, pectoral axial scale (pectoral fin has been moved downwards). Presumably the principal force involved in raising the cranium is provided by the long tendinousfibres of the upper section of the epaxialis and the medial bands of tendon. The forces directedtoward the midline and resulting in the elevation of the cranium are partially resisted by theinterlocking system of neural arches and supraneurals (see p. 165) which preserve the shape andrigidity of the dorsal profile. The absence of true myosepta in the dorsal section of the epaxialisand the low angles of inclination of the fibres to the medial vertical plane demand the fibresshortening over long distances. The lateral beams provided by the cranial intermuscular boneswould appear to form a rigid framework for this rather elastic movement. The lower part of theepaxialis which is attached laterally to the intermuscular bone beam, is arranged in helical layers(see p. 161). This arrangement of the muscle presumably aids in providing the necessary degreeof lateral body bending. The application of the term 'beam' to the unit of intermuscular bones although employedabove in a descriptive sense can also have a functional usage. As Alexander (1968) has explained,if a beam is long and thin, tensile and compressive stresses acting on it will be high and if thebeam is too slender it will fail by sideways bending. In Macrochirichthys the individual com-ponents of the beam, which can be thought of as elastic-like rods, allow the unit a great flexibilityin the vertical plane (Fig. 39B). Each rod (bone) forms an arc when the skull is bent upwards(see Figs 39A & B) and its flexibility provides a restorative force to straighten the cranium.Likewise the flexible nature of the 'beam' allows twisting and bending in the horizontal plane.The tapering and thickening of the beam at its proximal end coincides with the point at whichbending moments are greatest (see Alexander, 1968, 1969). The fact too that each bone of the THE ANATOMY OF MACROCHIRICHTHYS MACROCHIRUS 183 Fig. 39 Macrochirichthys macrochirus. Diagrammatic drawings of cranium, vertebral column andpectoral girdle showing association of the various elements when the cranium is elevated. A. Normalposition. B. Elevated position of a manipulated preserved specimen, the dashed outline indicatesthe presumed position of the cranium and pectoral girdle in a living fish. Note: pivoting of pectoralgirdle against lateral process of 2nd vertebra; bending of the cranial intermuscular bone beamand the enlarged 2nd-3rd intervertebral disc (black). Drawings made from radiographs. beam is longer than the one above it suggests the equal proportioning of tensile and compressivestresses. The widely spaced and obliquely orientated bands of fibres of the lateral epaxialis allowsthe intermuscular bones to move relative to each other. The downward movement of the pectoral fins would tend to rotate the pectoral girdle, therebyreinforcing the dorsal movement of the cranium effected through the system outlined above. It was noted (p. 177) that the upper part of the cleithrum is only narrowly separated from,and attached by ligamentous tissue to, the transverse process of the 2nd vertebra. When thepectoral girdle is rotated the tip of the cleithrum pushes back against this process, which thusacts as a pivot (Figs 39 & 40). Small aquarium specimens of Macrochirichthys are capable of rapid upward jerks of thecranium which at times make the head appear to lie almost at right angles to the horizontal axisof the body. The specimens in question were kept alive for less than 24 hours and were not fed,the head movements appeared to be a response to disturbance of their container. In preservedmaterial, the cranium when maximally elevated, lies at an angle of 30-35 to the vertebral column. The morphology of the cranial-vertebral joint in Securicula and Chela suggests that thesespecies too are capable of a similar degree of head movement. Confirmation that this does indeed 184 G. J. HOWES occur in Chela comes from the observations of Dr C. C. Lindsey. Lindsey(in press) found thatChela maassi could snap its head back almost at right angles to the contour of the back, that theelongate pectoral fins moved downward and that the fish was thus thrust upward. This 'neck-bending' and pectoral fin movement was used by the fishes when alarmed; if they were close tothe water surface when the neck-bending occurred they would break through. Lindsey also notedthat Chela skittered over the water surface, probably by utilizing rapid sequences of neck-bending.Possibly this action, as well as allowing predator-avoidance, might also be used for catchingprey at, or even above, the surface. As mentioned earlier (p. 173) the mouth of Chela is almostcircular and if the head was almost vertical when it hit the water surface the mouth would act likea funnel. 3 mm Fig. 40 Macrochirichthys macrochirus, pivot between cleithrum and 2nd vertebra. Whether or not Macrochirichthys can elevate its head to the same degree as can some species ofChela, the head shape, orientation and length of jaws, and the elongation of the body suggest arather different feeding action, one akin, in fact, to that of the characoids Rhaphiodon and Hydro-lycus (see below). In an earlier paper (Howes, 1976) I compared Macrochirichthys with the cynodontid characoidRhaphiodon using these genera as an example of parallel evolution. Although almost exactlyalike in external morphology, there are many differences in skeletal and muscle anatomy. The crania of the two genera are alike in the angle at which the neurocranium is orientated tothe vertebral column, and in the close union of the orbitosphenoid and the parasphenoid. How-ever, in the characoid a large area of the cranial roof (the frontal and sphenotic) is utilized for theattachment of the dilatator operculi muscle, whereas in the cyprinid the cranium is largely coveredby the extensive epaxial musculature, the dilatator operculi being small and originating onlyfrom the sphenotic. THE ANATOMY OF MACROCHIRICHTHYS MACROCHIRUS 185 Lesiuk & Lindsey (1978) have shown that Rhaphiodon is capable of a high degree of elevationof the cranium. The mechanism of this elevation differs from that of Macrochirichthys in that thearticulation of the head with the vertebral column is behind the Weberian apparatus. This hasnecessitated a modification to the anterior part of the swimbladder (see Lesiuk & Lindsey, 1978).As explained above (p. 162) in Macrochirichthys articulation of the cranium with the vertebralcolumn is between the basioccipital and the 1st vertebra and thus there is no modification of theswimbladder. One further convergence between the two genera is the development in Macrochirichthys oflong cranial intermuscular bone bundles and in Rhaphiodon of a cable-like tendon (see Lesiuk &Lindsey, 1978). No doubt these elements perform a similar function in both genera (see p. 182).It seems likely that the tendon in Rhaphiodon is the prime force in raising the cranium whereasthe intermuscular bones in Macrochirichthys have a more complex function (see p. 182). The precise method of prey capture by Macrochirichthys must await detailed analysis of suchaction in live specimens. It seems likely that the fish makes rapid darting movements towards itsprey from an almost stationary position. Approach is possibly from below, Macrochirichthysarresting its speed by extending the pectoral fins laterally and forward and seizing the prey by arapid backward jerk of the head. Some evidence for this method of capture comes from personalobservations, and from first-hand accounts of the feeding behaviour of Hydrolycus, a characoidclosely related to Rhaphiodon (see above). Hydrolycus makes rapid spurts forward and slashes atits prey, which it sometimes 'throws' or tosses before swallowing it. Relationships of Macrochirichthys Nomenclatural note In the following analysis the name Parachela is used. The genus is defined on p. 189, but itsintroduction at this point is necessary to facilitate the discussion of relationships. Parachelaincludes all those species presently assigned to the genus Oxygaster, with the exception of O.anomalura which now remains the sole representative of the genus Oxygaster. Macrochirichthys belongs to a group of genera characterized by the possession of the followingsynapomorphies : 1. A short supraethmoid overlapped by the frontals (see p. 152). 2. Narrow, medially depressed frontals with anteriorly converging canals (p. 151). 3. Modified triangular kinethmoid, sometimes articulating directly with the premaxillaries(p. 152). 4. Socket locking premaxillaries (p. 172). 5. Parasphenoid contacting pterosphenoid (p. 156). 6. A modified 1st centrum (tapered and anteriorly rounded) and second centrum (p. 162). 7. Neural complex sloped backwards and sometimes articulating with the first supraneural(p. 165). 8. Anterior supraneurals modified and articulating with succeeding elements (p. 165). 9. Horizontally aligned cranial intermuscular bones (p. 158). 10. Coracoid with a deeply incised ventral border or a reduced cleithral-coracoid fenestra(p. 177). 11. Short upright cleithral limb (p. 177). 12. Narrow, elongate supracleithrum (p. 177). 13. Modified postcleithrum (p. 177). 14. Anterior cranial extension of epaxial musculature (p. 150). Characters 1, 3, 6, 11 and 13 are possessed by all the taxa included in the group, i.e. Macro-chirichthys, Parachela, Oxygaster, Securicula, Salmostoma and Chela. This assemblage is hereafterreferred to as the cheline group (see p. 187). Characters 1 and 3 are also found in Rasbora, Rasborinus, Aspidoparia and Danio; characters 2(part), 10, 1 1 and 14 are present in Pelecus. These genera are discussed on pages 191-194. Chela can be immediately separated from the other cheline group genera on the basis of itscranial, pectoral girdle and axial skeletal morphology. The head is broad (wide frontals and 186 G. J. HOWES supraorbitals); the mesethmoid protrudes far laterally on either side of the reduced supraethmoidand extends forward as a shelf (p. 154 & Fig. 8); the preethmoids are minute (p. 154); the kine-thmoid is a small triangular lamellar bone (see Fig. 5D); the parasphenoid and orbitosphenoidare connected via a deep orbitosphenoidal septum; the dentary is extremely shallow; the enlargedsupracleithrum almost covers the upright limb of the cleithrum (Fig. 36E); the fenestra betweenthe coracoid and cleithrum is reduced or absent; the transverse processes on the 1st vertebra areenlarged and caudally directed; the supraneurals are enlarged, lamellar and interlock. The modifications of the ethmoid region; the shape of the mouth (p. 173), and the deep body areadaptations associated with a trend toward specialized surface or aerial feeding habits (p. 184).These several autapomorphies characterize Chela as representing the sister group of the othergenera included in the cheline assemblage (see cladogram, Fig. 41). Salmostoma (with Securicula; see below) appears to represent the plesiomorph lineage of thecheline group. It displays what might be regarded as 'first-stage' modifications resulting in theapomorph character complexes present in its sister taxa. The frontals barely overlap the supraethmoid; the kinethmoid is rod-shaped; the infraorbitalsare expanded and the 5th contacts the supraorbital ; the orbitosphenoid contacts the parasphenoidthrough a deep and narrow septum; the coracoids, although meeting each other along the midline,are not greatly expanded; the neural complex is long with an inclined dorsal border but isseparated from the fourth neural spine; a quadrat e-metapterygoid fenestra is present; the analfin is short (14-20 rays). Derived features in Salmostoma are the deeply notched ethmovomerine block; wide lateralcommissure; trigemino-facialis foramen situated within the prootic face; laterally extendedparietals ; narrow elongate supracleithrum ; reduced postcleithrum ; acutely angled jaw with well-developed symphysial process (in some species; see p. 190). Securicula, whilst retaining certain plesiomorph features (i.e. metapterygoid-quadrate fenestra;large 5th infraorbital contacting the supraorbital; short anal fin), possesses all the apomorphcharacters listed on p. 185, with the exceptions of 4 and 7. Although sharing with Macrochirichthys,Parachela and Oxygaster the incised coracoids, with Macrochirichthys and Parachela the mediallydepressed frontals and extended epaxial musculature, and with Macrochirichthys the contactbetween pterosphenoid and parasphenoid an even closer relationship with Salmostoma is suggestedby the following synapomorphies: anterior trigemino-facialis foramen within the prootic (p. 156);narrow, elongate supracleithrum (p. 179); lateral processes of second centrum posteriorly directed,reduction of postcleithrum ; elongate axillary scale. On the basis of these characters I considerSecuricula to represent the sister group of Salmostoma. Oxygaster possesses 1, 3, 6, 7, 10, 11 and 13 of the apomorph characters listed on p. 185. Itshares only with Parachela and Macrochirichthys the kinethmoid articulating with the pre-maxillaries, the elongate curved postcleithrum, and the long anal fin (26-36 rays; see below). Plesiomorph features of Oxygaster are the flat cranial roof with the frontal sensory canalsconfined to the lateral edge of the bones; well-developed dilatator fossa; lamellar supraneurals;a straight lateral line; large scales. Oxygaster is here recognized as a monotypic genus (see p. 187) which, together with Macro-chirichthys and Parachela, forms a sub-lineage of the cheline assemblage (see p. 187). Parachela possesses all the apomorph characters listed on p. 185 apart from 5, 9 and 12. Itshares only with Macrochirichthys the converging frontal canals, socket locking premaxillariesand elongate anterior supraneurals. Despite these synapomorphies there is still a large morpho-logical 'gap' between the two genera. Like Chela, Parachela snows a trend towards a specializeddeep-bodied habitus in which the lateral line is strongly decurved and follows the ventral borderof the body. From what has been said above Macrochirichthys is seen to belong to a subgroup of the chelineassemblage which also includes Oxygaster and Parachela. Macrochirichthys has tended towardsan elongation of the body and, a correlated elongation of the anal fin, a character shared withthe other two genera included in its subgroup (24-26 anal rays in Macrochirichthys; cf. 26-30 inOxygaster and 26-36 in Parachela). Although Macrochirichthys is more highly derived thanParachela in terms of the specialized nature of the vertebral column and associated musculature, THE ANATOMY OF MACROCHIRICHTHYS MACROCHIRUS 187 it still retains the overall plesiomorphic fades of the cheline group. Although Parachela lacks thehigh degree of vertebral modifications of Macrochirichthys, or even Chela, the morphology ofthe 1st and 2nd centrum and the anteriorly extended epaxial musculature suggest that it too iscapable of elevating the cranium to a marked degree. Thus, to summarize the interrelationships of the cheline group, it appears that the salmostominelineage (i.e. Salmostoma and Securiculd) form the sister group to the oxygastrine lineage (i.e.Macrochirichthys, Parachela and Oxygaster}. Within this assemblage Macrochirichthys andParachela share a common ancestor and form the sister taxon to Oxygaster. The salmostomineand oxygastrine lineages together comprise the sister group of the cheline lineage (i.e. Chela);see cladogram, Fig. 41. Macrochirichthys, Parachela and Oxygaster have an almost completely overlapping distributionthroughout the south-east Asian Archipelago, although, Oxygaster has not been recorded fromThailand or the Mekong drainage. Salmostoma is confined to India and Burma and its closestrelative, Securicula, to eastern and northern India. Chela is widespread throughout India and thesouth-east Asian Archipelago. One explanation of this distribution would be to suppose that the ancestral group whichgave rise to the lineages now represented by the cheline group was present in India (or proto-India). If it be accepted that Salmostoma represents the plesiomorph lineage of this group, thenit is likely that the basal dichotomy between the salmostomine and cheline lineages occurred inthat subcontinent with subsequent establishment of the cheline (i.e. Chela) lineage in south-eastern Asia. Securicula is seen as evolving from the salmostomine lineage within India. Theoxygastrine assemblage, however, appears to have developed only within the south-east AsianArchipelago. The cheline group: taxonomy and interrelationships Fowler (1905) first introduced the name 'Chelinae' under which he listed only Macrochirichthys.No definition of the Chelinae or indication of their status was given, but the use of the stem'Chela' in this name implied the inclusion of the genus Chela with Macrochirichthys. Subse-quently, Fowler (1934) placed both genera in the Abramidae, thus following the classification ofWeber & de Beaufort (1916), a practice adhered to by all subsequent authors. I have used the name cheline as an informal category and have purposely avoided its use as asubfamilial term because the interrelationships of this group with other taxa is at present imper-fectly known (see Howes, 1978). The most recent author to consider the taxonomy of the genera now assigned to the chelinegroup is Banarescu( 1967, 19680, 1968c, 1969, \91\a). Most of these taxa he placed in the Cultrinae(Banarescu, 1967). Despite Banarescu's work there remain many problems concerning thetaxonomy of the species now placed in the cheline group, and these are considered below: Macrochirichthys Bleeker, 1860 Type: Leuciscus uranoscopus Bleeker, 1850 (=Leuciscus macrochirus Valenciennes, 1844) Fowler (1905) described a second species of Macrochirichthys from Borneo, M. snyderi. Thisdescription was based on a single specimen which differed from specimens of M. macrochirus inpossessing dark transverse bands across the nape. Later, Weber & de Beaufort (1916) placedM. snyderi in the synonomy of M. macrochirus. Fowler (1934) contested this decision, not onlymaintaining the validity of his species but describing yet another, M. laosensis from the MekongRiver. Smith (1945), correctly in my opinion, relegated both M. synderi and M. laosensis to thesynonomy of M. macrochirus. Oxygaster van Hasselt, 1823Type : Oxygaster anomalura van Hasselt, 1 823 From the foregoing analysis it will be evident that there are major differences between the type 188 G. J. HOWES 1) 13ol e - THE ANATOMY OF MACROCHIRICHTHYS MACROCHIRUS 189 species of the genus O. anomalura and the other species presently assigned to the taxon (seeBanarescu, 1969). The differences between the species are listed below: Oxygaster anomalura Other Oxygaster species Epaxial musculature extends to parietal Epaxial musculature extends to anterior of frontals Frontals flat or convex, sensory canals confined Frontals depressed medially, canals convergingto lateral edges anteriorly Well-developed transverse parietal ridge Parietal ridge absent Long lower jaw with symphysial process Short lower jaw with reduced symphysial process Lateral process of 4th vertebra curved posteriorly Lateral process of 4th vertebra curved anteriorly Angle of neural complex to vertebral column 35 Angle of neural complex 40-45 Anterior supraneurals lamellar Anterior supraneurals rod-shaped Kinethmoid expanded dorsally Kinethmoid curved anteriorly Coracoids barely indented Coracoids deeply incised Supracleithrum elongate Supracleithrum short These morphological differences show that apart from cheline synapomorphies, Oxygasteranomalura possesses no other (derived) characters of the other Oxygaster species. I thereforeconsider that these other species be assigned to the genus Parachela (see below). Parachela Steindachner, 1881 Type : Parachela breitensteini Steindachner, 1881 (= Chela hypophthalmus Bleeker, 1860) This genus was characterized by Steindachner by its lacking of ventral fins. However, the descrip-tion was based on a single, aberrant specimen (see below). Apart from this abnormality Parachelabrietensteini possesses all the characters listed above under the heading 'Other Oxygaster species'.In accordance with those characters the species assigned to Parachela are : P. oxygastroides (Bleeker, 1852)P. hypophthalmus (Bleeker, 1860)P. pointoni (Fowler, 1934)P. williaminae Fowler, 1934P. maculicauda (Smith, 1934) Through the courtesy of Dr P. Kahsbauer I have been able to examine the holotype andunique specimen of Parachela breitensteini. There is no trace of ventral fins nor any part of thepelvic girdle (ascertained by radiography). Although abnormal in this respect, all other morpho-logical and meristic characters show that P. breitensteini is a specimen of Parachela hypophthalmus(Bleeker, 1830) and should thus be included in the synonymy of that species. Fowler (1934) described a second Parachela species, P. williaminae which he placed in a sub-genus, Grandisquamachela, distinguished from Parachela by its larger scales (35 in the lateral line,cf. 60 in P. breitensteini. Banarescu (197 la) found that Fowler's (1934) description was also basedon an aberrant specimen and placed the species in the genus Oxygaster. I have not seen the typeof P. williaminae and so am provisionally accepting Banarescu's (1971#) contention that it is avalid species and is related to P. oxygastroides. The species here assigned to Parachela were revised by Banarescu (1969) and for the most part Iagree with his synonymies. However, concerning the taxon pointoni, Banarescu (1969) recognizedChela pointoni Fowler, 1934 as a valid species (of Oxygaster, i.e. Parachela) but later (Banarescu,1971a) he considered it to be a subspecies of Oxygaster anomalura van Hasselt, 1823. I have notseen the holotype of this species but from Fowler's description and the photograph published by 190 G. J. HOWES Banarescu (1969) it is clear that the epaxial muscles extend forward to the interorbital area andtherefore the taxon should be referred to the genus Parachela. Its specific status must remain indoubt; according to Banarescu (1969) there are '. . . some 36 scales' in the lateral line, yet later(1971a) he gives a count of 43-44; Fowler (1934) in his original description gives 33. If Banarescu's197 la description is correct then I see no reason why P. pointoni should not be included in thesynonymy of P. oxygastroides. Taki (1974) records P. pointoni from Laos, but his photograph isof an Oxygaster species, close to, or identical with O. anomalura. Salmostoma Swainson, 1839Type: Cyprinus bacaila Hamilton-Buchanan, 1822 This genus belongs to the plesiomorph sister-group of the oxygastrine lineage (see p. 187). Themost recent revision is by Banarescu (19680) who recognizes 10 species. I have the followingcomments concerning these species. Salmostoma bacaila (Hamilton-Buchanan, 1822). The development of the symplectic and theassociated metapterygoid-quadrate fenestra in this species have been commented on earlier(p. 175). It was considered that the nature of this feature, together with the long jaws, are indica-tive of a relatively derived status. This is further indicated by the elongate, deeply notchedethmoid region and the well-developed symphysial hook on the lower jaw. Banarescu (19680)states that this species is '. . . the most frequent of all', but then notes that its range is restrictedto the Indus and Ganges drainages. Salmostoma clupeoides (Bloch, 1782). As Banarescu (19680) suggests, this species may simplybe a subspecies or perhaps a clinal group of S. bacaila from which it appears to differ onlyin the number of lateral line scales. Salmostoma phulo (Hamilton-Buchanan, 1822). I cannot agree with Banarescu's (19680)division of this species into two subspecies, separated by a difference in the number of lateralline scales (99-1 12 in phulo phulo cf. 76-86 in phulo orissaensis). Later, Banarescu (19710) recordedthe subspecies orissaensis from Madras based on a single specimen with a lateral line count of89, thus extending the range of this 'subspecies' for a further 700 miles. I have examined the typesof S. phulo orissaensis and find many differences, apart from lateral line scale counts, betweenthem and specimens of S. phulo phulo (e.g. shape of the 5th infraorbital; interorbital width;pectoral fin length; lower jaw length; shape of axillary scale), all of which Banarescu has ignoredbut which I believe indicate specific rather than subspecific status. Salmostoma punjabensis (Day, 1872). Banarescu (19680) suggests that this taxon is possibly asubspecies of S. phulo. This is highly unlikely as 5 1 . punjabensis is known only from the Indus andS. phulo only from Assam, a separation of some 28 of latitude. My own comparison of the twotypes suggest these are indeed two quite distinct species characterized by differences in snout,jaw and pectoral fin length. Banarescu (19680) does not give measurements of the pectoral finlength which appears to be an important character in separating species of this genus. Salmostoma horai (Silas, 1951). Banarescu (19680) did not examine any specimens but acceptedthis as a valid species on the basis of Silas' description. Silas (1951) remarks that the lower jawhas a well-developed symphysial process and that the species differs from its congeners inpossessing short vertical bands along the flanks. Salmostoma acinaces (Valenciennes, 1842). A large scaled species which will probably prove tobe polyspecific. Salmostoma untrahi (Day, 1869). Banarescu (19680) noted the vertically aligned mouth and thelong symphysial process of the lower jaw, this process is not developed in a specimen of 65 mmSL. Elsewhere I have commented on these features (p. 186) and suggest that S. untrahi repre-sents, like S. bacaila, a specialization towards the morphotype of Securicula. Salmostoma boopis (Day, 1869). Banarescu (19680) notes. This species is close to S. acinaces,differing from it in number of scales, rays and gill rakers (but with overlap of extreme values!)'.I find that there is an overlap in all meristics and it seems likely that S. boopis is a synonym ofS. acinaces (part). Salmostoma sardinella (Valenciennes, 1842). Comments have already been made concerning THE ANATOMY OF MACROCHIRICHTHYS MACROCHIRUS 191 the form of the metapterygoid-quadrate fenestra in this species (p. 175) and its relatively special-ized nature. Salmostoma sladdoni (Day, 1869); the only species of the genus apparently restricted to Burma. Banarescu (19680) groups the species of Salmostoma into four lineages on the basis of geo-graphical distribution. Such a grouping is impossible on the material currently available, thetotal collections of which amount to c. 150 specimens (based on Banarescu, 19680). This interest-ing genus must be critically revised on an osteological basis before any assumptions can bemade concerning intra-generic relationships. Securicula Giinther, 1868 Synonymy: Pseudoxygaster Banarescu, 1967 Type : Cyprinus gora Hamilton- Buchanan, 1 822 Banarescu (1967) erected the genus Pseudoxygaster for the species gora which previously hadbeen assigned by various authors to either Chela or Oxygaster. Giinther (1868) had divided thegenus Chela into two sections on the grounds of differences in the pectoral girdles. One of thesedivisions he named Securicula and included gora as the first-named species. Jordan (1919)recognized gora as the type species of Securicula by logotypy. Banarescu (1967, 19680) treatedSecuricula as a synonym of Salmostoma, presumably on the assumption that the other specieslisted by Giinther under Securicula are now recognized as belonging to the genus Salmostoma.I can find no grounds for not recognizing Securicula as a distinct taxon and accordingly treatPseudoxygaster as its junior synonym. The genus is monotypic, although Banarescu (1967) considered the possibility that there aretwo subspecies, an opinion based on a single specimen having fewer lateral line scales than thetype. Banarescu (1967) thought Securicula to be closely related to Macrochirichthys and Pelecus.Mirza, Alam & Kausar (1974) and Mirza (1975) noted the presence of the metapterygoid-quadratefenestra and Mirza (1975) considered the genus to be 'the most primitive of the Cultrinae ofsouth Asia'. Contrary to this opinion I believe Securicula is the most highly evolved member ofthe Salmostomine lineage (see p. 187). Chela Hamilton- Buchanan, 1822Type: Chela cachius Hamilton-Buchanan, 1822 The most complete revision of the genus is that of Silas (1958) who recognized the subgeneraAllochela and Neochela on the basis respectively of a complete or incomplete lateral line.Banarescu later (1968c) recognized a third subgenus Malay ochela with the pharyngeal teetharranged in two instead of three rows as in the other taxa. However, Banarescu states that thisis a variable character in other cyprinid genera - which it is - and therefore I see little to justifythe subgenus Malayochela. There are, on the other hand, distinct differences in the developmentof the transverse processes of the 1st and 2nd vertebrae. Whether these differences are speciesspecific or whether they can be used to define groups of species remains to be verified. The relationships of Chela have been discussed on p. 186; the genus is seen as representing ahighly evolved group of surface or aerial feeding specialists which departed early from the basiccheline stock. Of the characters listed on p. 185 defining the cheline group, one - the frontals overlying thesupraethmoid - is shared with Aspidoparia, Rasbora, Rasborinus and Danio; furthermore, asecond feature - the expanded kinethmoid - is found in all but Aspidoparia. These four generapose acute problems in determining phylogenetic relationships and will be discussed in greaterdetail. Aspidoparia Heckel, 1843 Type: Aspidoparia sardina Heckel, 1843 ( = Cyprinus morar Hamilton- Buchanan, 1822) This genus shares with the other taxa assigned to the cheline group a short, triangular supra-ethmoid; anteriorly the ethmo-vomer block is deeply notched and posteriorly the supraethmoid is 192 G. J. HOWES covered by the frontals. However, the entire ethmoid block is short and strongly decurvedanteriorly. Aspidoparia also shares with other chelines an elongate first supraneural whicharticulates with the neural complex. As in Salmostoma the kinethmoid is rod-shaped, the infra-orbitals large (the 5th contacting the supraorbital), the orbitosphenoid is joined to the para-sphenoid by a deep septum and there is a metapterygoid-quadrate fenestra (the smallest apertureof this nature in any of the genera possessing it - see p. 177). All these characters shared withSalmostoma are plesiomorph for the cheline group, as are the gently curved lateral line andshort anal fin (9-12 rays). Aspidoparia differs from other genera assigned to the chelines in the following features;the 1st vertebra is neither anteriorly tapered nor rounded and it bears strong, somewhat anteriorlydirected lateral processes; the neural complex is upright and not inclined backwards ; the cleithrumis upright and has a high anterior ridge along its horizontal arm (resembling the condition inDanio); and finally the reduced parietals and well-developed supraoccipital process. The jaws of Aspidoparia are markedly different from any cheline or for that matter, anycultrine. They are short, the lower jaw being curved strongly medially and the entire mouthinferiorly placed. The coronoid process of the obliquely angled dentary is situated at the middle ofthat bone. From the roof of the mouth there hangs a thick papillose nodule originating frombelow the vomer. The intestine of Aspidoparia is much coiled (the specimens dissected containedfine mud and silt in the gut). Sorescu (1968) placed Aspidoparia amongst the cultrines because of resemblances between itspectoral girdle and those of certain other genera. By my definition of the cultrine group Aspidopariacannot be placed there (p. 197). The synapomorphies mentioned above may be indicative,however, of a shared common ancestry between Aspidoparia and Salmostoma, in which caseAspidoparia can be seen as representing a specialized detrivorous branch of the cheline group(see Fig. 41). There appear to be two species of Aspidoparia; A. morar (Hamilton- Buchanan, 1822) andA.jaya (Hamilton- Buchanan, 1822). The species siamensis Sauvage, 1881, originally placed in thegenus Morara, was placed in Aspidoparia by Smith (1945). He quoted Pellegrin as saying thatsiamensis did not belong to Aspidoparia, but although Smith included it in that genus he did sowith hesitation. I have not seen Sauvage's specimens of Morara siamensis and so the correctplacement of this taxon must await a revision of this species group. As mentioned above (p. 191) three other genera also share some of the characters used indefining the cheline group. These are Rasbora, Rasborinus and Danio. The ethmoid region of some Rasbora species (including the type of the genus, R. rasbord)closely resembles that of Chela in that the mesethmoid extends laterally beyond the borders ofthe supraethmoid and protrudes as a shelf; the kinethmoid is also of the same lamellar type.Not all species of Rasbora possess these characters and some species (i.e. R. argyrotaenia andR. dusonensis) share derived characters with Luciosoma. In Rasborinus and some species of Danio the ethmo-vomer is deeply notched anteriorly as inthe chelines and cultrines (see p. 194). As with Rasbora there is a similar problem concerning the genus Danio. The species I haveexamined appear to have marked differences in certain characters, particularly in the form ofthe lower jaw. In Danio dangila, the type of the genus, the antero-ventral part of the dentarybears a semicircular notch, there is a strong lateral flange on the coronoid process of the dentary,and the kinethmoid is of a type closer to that of Rasbora than to the other Danio species. InDanio malabaricus, D. aequipinnatus and D. spinosus the kinethmoid is of the lunate type illustratedin Fig. 5E; the notch on the ventral surface of the dentary is widely separated from its fellowalong the midline, thus forming a characteristic arrow-shaped gap when viewed from below(Fig. 42), and there is a crenelated fleshy ridge along the margin of the lower jaw. Danio devariodiffers from all these species not only in the rhomboidal form of the body but in the morphologyof the ethmoid region, which resembles that of Chela. It lacks, however, any of the charactersused to define the cheline group, apart from the overlapping of the dermethmoid by the frontalsand the triangular lamellar kinethmoid. The composite genera Danio and Rasbora must be revised before any phylogenetic relationships THE ANATOMY OF MACROCHIRICHTHYS MACROCHIRUS 193 can be established between their various included taxa. Thus, at present I cannot say if Rasborasensu stricto, Danio sensu stricto and Rasborinus are more closely related to the cheline than toany other group; indeed I am not even sure that the three taxa are closely related to each other. 2mm Fig. 42 Danio malabaricus, ventral aspect of the lower jaw. Although Rasbora sensu stricto, Danio sensu stricto and Rasborinus share with the chelinegroup similarly modified ethmoids, there are no similar vertebral modifications. Whether suchchanges in the ethmoid region (i.e. overlap of the supraethmoid by the frontals) must necessarilybe correlated with rearrangements in the structure of the vertebral column - as seems to havebeen the case in the chelines - is uncertain. However, studies on the African cyprinid generaEngraulicypris and Chelaethiops indicate that such changes in the ethmoid region are a 'pre-requisite' to vertebral modifications. Comments on the Cultrinae and relationships with the cheline group The problem now remains as to the relationships of the cheline group with other assemblagesof cyprinids and in this context the interrelationships of the taxa referred to the subfamilyCultrinae (to which the cheline genera are currently assigned) must be evaluated. Of all the cyprinid subfamilial assemblages recognized at present there is probably none soill-defined as the Cultrinae. Nikolsky (1954, 1955) first used the subfamily designation to includesome genera which had previously been placed in the Abramidae, Xenocyprinidae and Danio-ninae. Silas (1958), in his review of Chela, pointed out that the Abramidinae (he made no mentionof the Cultrinae; no doubt having overlooked Nikolsky's introduction of the taxon) seemed agroup of convenience rather than a natural assemblage and thought that it included two majorsub-groups, one in Thailand and the Malayan sub-region, the other in China. Banarescu (1967) reviewed the Cultrinae, outlined its taxonomic history and pointed out thedifficulties in defining the taxon. The characters Banarescu used were entirely superficial andapparently indiscriminate ones, and although he thought the subfamily represented a mono-phyletic unit he produced no arguments to show why. In fact his statement that the monophyly 194 G. J. HOWES of the Cultrinae is 'less evident' than that of some other subfamilies, and again 'the relationshipsbetween these genera are obscure' indicates Banarescu's uncertainty about the monophyleticintegrity of the 21 genera he included in this group. Later, Banarescu (\91Qa) makes the pointthat the 'delimitation of the genera within the Cultrinae is difficult and rather arbitrary, whilethe species are in general well-differentiated'. Sorescu (1968) studied the pectoral girdle in various cyprinids. On the basis of this study shemade radical taxonomic changes by placing Aspidoparia morar, Barilius zambesensis and Alburnusalburnus in the Cultrinae. However, as pointed out by Howes (1978), she misinterpreted varioussimilarities as indicating relationship instead of parallelism, and made no attempt to support herconclusions by using other morphological characters. During the course of studying Macrochirichthys I have had the opportunity to examinerepresentatives of the genera placed in the Cultrinae by Banarescu (1967) and by Sorescu (1968).The following comments may serve to clarify the taxonomy and interrelationships of these taxa. Cutter Basilewski, 1855Type: Culler alburnus Basilewsky, 1855 Erythroculter Berg, 1909Type: Culler erylhroplerus Basilewsky, 1855 Ischikauia Jordan & Snyder, 1900Type: Opsariichlhys sleenackeri Sauvage, 1883 These closely related genera can be considered together. All three share an almost identicalcranial anatomy, i.e. deeply notched ethmoid, an anteriorly projecting vomer, well-developed andovate preethmoids, narrow skull, long post-parietal platform (formed from the supraoccipital,parietal and epioccipital - see Howes, 1978), truncated supraoccipital process, well-developedposttemporal fossae, large dilatator fossae, formed from the frontal and sphenotic, the sphenoticprocess produced latero-posteriorly, the orbitosphenoid and parasphenoid in close contact,extensive intercalar, wide ectopterygoid, a quadrate foramen, short upper and lower jaws with ahigh coronoid process on the dentary, and a wide, vertically aligned neural complex. Many of these characters are widespread amongst cyprinids and must therefore be regarded asplesiomorph. However, there are indications that the morphology of the ethmoid region, of thepost-parietal area of the cranium, and of the pectoral girdle, will provide useful characterspositively to link these genera with others considered below. Culler and Erythroculter differ from each other in the form of the lower jaw, which is alsoshorter in Culler (contained twice in head length, cf. 1-5 times in Erythroculter). The coronoidprocess is situated at the posterior end of the lower jaw in Cutter whereas it lies midway along thejaw in Erythroculter. Other differences are to be found in the width of the supraorbitals and lengthof the nasals. Ischikauia most closely resembles Erythroculter but differs both from that genus and fromCuller in possessing a flexible 2nd dorsal spine instead of a well-ossified one. Berg (1964 : 360) stated that Erythroculter is 'like Culler but abdomen keeled only behind theventral base'. I doubt whether such a character by itself has any use in determining generic-levelrelationships (see p. 180). Despite the fact that there have been two revisions of the genus Erythroculter (Yih & Chu,1959 -not seen; Banarescu, 1967) both this genus and Culler have been inadequately definedand much nomenclatural confusion still exists. Banarescu (1967), following Yih & Chu (1959),states that Culler erylhroplerus Basilewsky, the type species of the genus Erythroculter is in factsynonymous with Culler alburnus and therefore Erythroculter must become a synonym of Culler.As pointed out above there are significant differences between Culler and Erythroculter. In thecourse of this study specimens of Culler alburnus, Culler brevicauda, Erythroculter ilishaeformisand Erythroculter mongolicus were examined. The type specimens of Culler erylhroplerus areapparently lost (Banarescu, 1967) and if, as seems likely from the description of Basilewsky (1855),erylhroplerus is a synonym of alburnus, then Erythroculter must be a junior synonym of Culler.But, since there are synapomorph characters relating the species ilishaeformis, dabryi, hypselo- THE ANATOMY OF MACROCHIRICHTHYS MACROCHIRVS 195 notus, oxycephaloides and mongolicus which are not possessed by those referred to the genusCuller, the former group will have to be referred to the genus Chanodichthys Bleeker, 1860 (thenext available name) with mongolicus as the type of the genus. The nomenclatural problem concerning the type species of the genus Culler was satisfactorilyresolved by Myers (1940). This genus is in need of a thorough revision and the generic status ofsome species (e.g. C. lienlsinensis Abbott, 1901 and C. kashinensis Shaw, 1930) has to be clarified. Longiculter Fowler, 1937Type: Longiculter siahi Fowler, 1937 This is a perplexing taxon known only from the unique holotype. Fowler's (1937) statement thatLongiculter differs from other cultrine genera in the elongate and compressed body means virtuallynothing (see Smith, 1945). What is important is that the species appears to possess over 100 gill-rakers (rarely above 30 in cultrines and oxygastrines). Banarescu (1967, 197 la) accepts Longiculter as a valid genus. In his 19710 paper Banarescusimply states 'Agree with Fowler's description', and he gives a gill-raker count of 107-128(Fowler gives 106). Both this genus and the Culler species recorded from Thailand need to be re-examined critically.Regrettably I have no specimens of these taxa to hand but I suspect that the 'Culler' of Thailandwill be found to be quite a different entity from the 'Culler' of China. Hora (1923) pointed outthe differences between Culler siamensis and the other species assigned to that genus (see alsoSmith, 1945 : 87 on this point). Whether these Thailand forms will have to be placed in thecultrine or cheline group must await the availability of further specimens. Megalobrama Dybowski, 1872Type: Megalobrama skolkovii Dybowski, 1872( = Megalobrama lerminalis (Richardson), 1 846) This genus has the same osteological characteristics as Erylhroculler, but the member species aredeeper bodied, have wider crania and less oblique mouths. One important character is thepresence of sharp-edged horny sheaths in the upper and lower jaws. The genus Sinibrama was established by Wu (1939) for the species Megalobrama macropsGiinther. Wu (1939) distinguished Sinibrama from Megalobrama on the basis of its shorter analfin and bipartite (cf. tripartite) swimbladder. Banarescu (19700) considered this division worthyof only subgeneric rank. However, there are differences in the structure of the mouth, the hornysheaths being absent in M. macrops, which also has a different pattern of fleshy folds in thebuccal cavity. I have also found differences in the structure of gill-rakers between macrops andother Megalobrama species. Parabramis Bleeker, 1864Type: Abramis pekinensis Basilewski, 1855 This genus has the same osteological characters as Erylhroculler. However, the infraorbitals aremore reduced than in that genus, the pharyngeal teeth are pointed and the ventral keel extendsforward of the ventral fins (although this character is of a somewhat dubious nature, see p. 180). Ancherythroculter Wu, 1964Type: Chanodichthys kuremalsui Kimura, 1934 I have been unable to examine specimens of any of the species assigned to this genus. Accordingto Banarescu (1967) Ancherythroculter is separated from Erylhroculler on the basis of a bipartite(cf. tripartite) swimbladder, differences in the length of the anal fin and the shape of the scales.Banarescu (19710) recognized these as 'good generic' characters but earlier (19700) in the case ofMegalobrama and Sinibrama had considered the same characters as worthy of only subgenericdistinction (see above). 196 G. J. HOWES Rasborinus Oshima, 1920 Type: Rasborinus takakii Oshima, 1920 ( = Rasborinus lineata (Pellegrin), 1907) Mention has already been made of the possible relationship between this genus and Danio(p. 192). Paralaubuca Bleeker, 1863Type : Paralaubuca typus Bleeker, 1 863 The osteology of the cranium and the axial skeleton is typically that of Culler. The distinctivecharacter of this genus lies in the two quite separate lateral lines on the anterior part of the body(in some specimens there may even be three; see Banarescu 197 16 : 348). Pseudolaubuca Bleeker, 1864Type: Pseudolaubuca sinensis Bleeker, 1864 The cranium is narrow and convex across the interorbital region. The orbitosphenoid andparasphenoid are widely separated by an orbitosphenoid septum. The ethmoid region, the firstvertebra and neural complex are like those of Culler. There is an elaborate development of thesupraneurals (see p. 170, Fig. 25) like that found in Chela. A parallel feature shared with Macro-chirichlhys is the lateral process of the hyomandibula. A revision of the genus was made byBanarescu (1964). Hemiculter Bleeker, 1859Type: Culler leucisculus Basilewski, 1835 The cranium is as in Pseudolaubuca, but the premaxillary processes are elongate. This genus isalmost identical with Toxabramis save for the possession of a non-serrated dorsal spine, acharacter which in other cyprinid genera (e.g. Barbus) is not indicative of generic status. Banarescu (1968ft) revised the species of Hemiculter but made no mention of the relationshipsof the genus. Toxabramis Gunther, 1873Type: Toxabramis swinhonis Gunther, 1873 Toxabramis is distinguished from Hemiculter because its pharyngeal teeth are in two and not threerows and it has a serrated and not a flexible dorsal fin spine. I have been unable to examine theosteology of Toxabramis in detail but superficial dissection of one of the syntypes of T. swinhonis,and an examination of radiographs, reveals a Culter-type organization of the cranial and axialskeletons. A revision of the genus was made by Banarescu (1963). Hemiculterella Warpachowski, 1887Type: Hemiculterella sauvagei Warpachowski, 1887 The cranium is wide and flat; the orbitosphenoids are closely joined with the parasphenoid; theinfraorbitals are large and the supraorbital almost contacts the 5th infraorbital. The lateral lineis deeply curved anteriorly and follows an erratic course. The dilatator fossa is small and roofedby the frontal. The second dorsal spine is well-ossified. The relationships of Hemiculterella are discussed below, p. 197. Possibly not all speciespresently ascribed to this genus should be included in it (see Banarescu, 197 la). Pelecus Agassiz. 1835Type: Cyprinus cullralus Linnaeus, 1758 The cranium is wide and flat posteriorly; the frontals are depressed medially and accommodatethe anterior extension of the epaxial musculature; the infraorbitals are reduced and the supra-orbital is small; the lower jaw is short and without a symphysial extension; the supraneurals are THE ANATOMY OF MACROCHIRICHTHYS MACROCHIRUS 197 well-developed; the lateral line is deeply curved anteriorly and follows an erratic course; thelateral line scales are numerous (90-1 15). Pelecus is the only supposedly European representative of the Cultrinae and was included inthis subfamily by Banarescu (1967) on the grounds of its close resemblance to Oxygaster andMacrochirichthys. However, it differs in many respects from those and other cheline genera. Thecranium, although showing a development of the frontals similar to that in Macrochirichthys,Parachela and Securicula, is wide posteriorly and has reduced parietals; an extensive auto-sphenotic accommodates a large dilatator and posttemporal fossae cf. pages 152-153); thesupraethmoid is posteriorly sutured to the frontals instead of being overlapped by them. AlthoughPelecus resembles the cheline genera in the alignment of the neural complex, there are markeddifferences in its basic morphology. The second neural plate is reduced; the neural complex isgreatly expanded antero-posteriorly and contacts the first supraneural above the 5th centrum,cf. 7th or 8th in Macrochirichthys; the supraneurals are lamellar. The 1st vertebra, althoughhaving a well-rounded anterior face, possesses broad lateral processes, the ends of which aredirected ventro-posteriorly. Other differences from members of the cheline group are evident inthe pectoral girdle. The upright part of the cleithrum in Pelecus is broadly lamellar; the supra-cleithrum extends halfway along the cleithrum; the postcleithrum is short and straight; theposterior border of the coracoid is straight and although, as in Parachela and Securicula, theventral coracoid border is incised, the nature of this indentation is quite different (see p. 180;cf. Figs 33B & 35C). Although, as already mentioned, Pelecus possesses some of the apomorph characters listed onp. 185 as defining the cheline group, it lacks the characteristic morphology of the ethmo-vomerineregion (p. 153). Furthermore, the vertebral column and pectoral girdle, although similar to thosestructures in the chelines are, in their basic morphology, more akin to those like structures insome leuciscines (see also Gosline, 1974 who includes Pelecus in the leuciscines). In short, theyare the result of parallel evolution. Perhaps it is more correct to consider this as convergentevolution when it is remembered that Pelecus spends much of its life in brackish water where itappears to behave in a rather clupeoid fashion. Thus, those features in which it resembles someof the cheline genera may have been acquired under the different selection pressures of an esturineenvironment. This has resulted in the evolution of similar pelagic characters to the chelines but indissimilar associations. A likely candidate as the closest relative to Pelecus is Hemiculterella. With this genus Pelecusshares the flat, posterior cranium; the extensive sphenotic and dilatator fossa and the zig-zaggedlateral line. To recapitulate; of the twenty-one genera listed by Banarescu (1967) as belonging to theCultrinae, only six are thought to constitute a monophyletic assemblage - the cheline group.Of the taxa placed in the Cultrinae by Sorescu (1968) Aspidoparia has already been discussed(pp. 191); Barilius zambesensis although belonging to a discrete group of bariliines (unpublishedobs.) possesses no derived characters which would include it amongst the cultrines; Alburnusalburnus may have a closer affinity with certain cultrines than do other taxa currently placed in theLeuciscinae. Of the remaining genera two related assemblages can be recognized. I The cultrine group, comprising Culter, Erythroculter, Ischikauia, Parabramis, Megalobrama and Paralaubuca, II The hemicultrine group, comprising Hemiculter, Pseudolaubuca and Toxabramis (possibly Rasboriichthys (part) should also be included here). Two other genera included in the Cultrinae by Banarescu (1967), Pelecus and Hemiculterella,are believed to be closely related to one another but not to any of the taxa listed above. Theirrelationships would seem to be with the Leuciscinae sensu lato. Rasborinus appears to be related to Danio (see p. 192), a genus not included in the Cultrinae byBanarescu (1967). The affinities of Ancherythroculter are at present unknown (p. 195), but do not appear to bewith the cultrine or hemicultrine groups. In his discussion on the relationships of the Cultrinae, Banarescu (1967) mentions the genusNematabramis which Weber & de Beaufort (1916) placed in the Abramidinae (thus including it 198 G. J. HOWES with Chela and Macrochirichthys). Banarescu (1967) does not accept any relationship betweenNematabramis and any of his cultrine genera but states that it is 'evidently related to the Danioinaeespecially to Esomus\ Nematabramis is a peculiar taxon; there are transverse ridges along thesurface of the frontal (Howes, 1978), a highly modified ethmoid region, a membraneous maxillarybarbel and other characters which do not immediately suggest a close relative. I can find noosteological evidence to suggest a close relationship between Danio sensu stricto and Esomus asis implied by Banarescu (1967, 1971ft). The other group mentioned by Banarescu (1967) as being a likely relative of the Cultrinae is thesubfamily Xenocypridinae. According to Banarescu (1970ft) the characters defining this subfamilyare: an inferior transverse mouth, smooth dorsal spine and compressed pharyngeal teeth withlong grinding surfaces. I have examined the type species of Xenocypris, X. argentea and findthat the dentary is extremely shallow and short, but it is broad so that medially it is narrowlyseparated from its fellow; the coronoid process of the lower jaw is high with a concave border;the ethmoid complex is deeply notched anteriorly and that there is an anterior chamber of thesubtemporal fossa. Two other genera are included in the Xenocypridinae, Plagiognathops and Distoechodon(sometimes recognized as subgenera of Xenocypris; see for example Nichols, 1943). Banarescu(1970ft) recognizes Plagiognathus as a valid, monotypic genus but Distoechodon as a 'polytypicsubgenus'! From my own limited observations it appears that there is considerable differencein the structure of the gill-rakers between these various taxa. For example, Plagiognathus microdonmore closely resembles Xenocypris (Disteochodon) tumirostris in this character than do either ofthese taxa resemble Xenocypris argenteus. As yet I have been unable to ascertain that they allshare the apomorph osteological characters of Xenocypris argenteus listed above. This entiregroup is in need of critical revision and like so many other cyprinid 'subfamilies' the Xenocypri-dinae appears to be polyphyletic. Mirza (1975) thought the Cultrinae to be most closely related to the Danioinae but in the lightof the comments concerning the composite nature of the genus Danio (p. 192) the designation'Danioinae' is meaningless. The basis Mirza chose for this relationship was the shared possessionof the metapterygoid-quadrate fenestra in some members of the Cultrinae and in Opsariichthysand Zacco (presently included in the Danioinae). As pointed out elsewhere (p. 177; Howes, 1978)this character is plesiomorphic for the cyprinids and so cannot be regarded as an indicator ofshared recent common ancestry. From work presently in progress it seems that Opsariichthys isnot related to any member of the cheline or cultrine groups; indeed, its closest living relatives arecurrently included in the genus Barilius. Thus, at present the identity of the sister-group to the chelines must remain in doubt. It seemsthat a likely candidate will be identified as a monophyletic assemblage of taxa included herewithin the cultrine and hemicultrine groups (p. 197). Conclusions Macrochirichthys' macrochirus is a highly specialized piscivore derived from an ancestral lineagenow represented by the genera Salmostoma and Securicula. These taxa are members of a mono-phyletic assemblage (the cheline group) in which three lineages can be recognized, viz. the cheline,represented by Chela; the oxygastrine, by Macrochirichthys, Parachela and Oxygaster, and thesalmostomine by Salmostoma and Securicula. Parallelism between Macrochirichthys and Securi-cula has in the past led to the erroneous assumption of their close relationship (Banarescu, 1967). The Cultrinae (Banarescu, 1967) have been shown to be a non-monophyletic assemblagealthough two groups of genera - the cultrine and hemicultrine - may be monophyletic. One ofthese is possibly the sister-group of the chelines. Macrochirichthys is capable of a great degree of cranial elevation, made possible by the balland socket connection of the basioccipital with the 1 st vertebra and modifications of the epaxialmusculature. Cranial elevation is also possible - perhaps to an even greater degree - in Chela.Salmostoma represents the plesiomorph lineage in which there are seen pre-adaptations to thisfunction, namely, a short post-parietal area with a posteriorly rounded cranium and a reduced THE ANATOMY OF MACROCHIRICHTHYS MACROCHIRUS 199 supraoccipital process; short ethmoid region overlapped by the frontals; rounding and shorteningof the 1st vertebra with reduction of its lateral processes; a caudal inclination of the neuralcomplex and modification of the anterior supraneurals. Such adaptations have resulted, on theone hand, in the evolution of forms such as Macrochirichthys and Securicula where the craniumis compressed and the dorsal musculature has extended across the skull roof; and on the otherhand, in Chela, where the cranium has remained broad and there has been little modification tothe dorsal muscle elements. Likewise, the protrusibility of the upper jaw is virtually lost inMacrochirichthys and Securicula but retained in Chela. Further comparison between Macrochirichthys and the characoid Rhaphiodon has highlightedthe major anatomical differences involved in achieving similar evolutionary status. It may beadded here that a neck-bending mechanism similar to that of Rhaphiodon appears to be presentin the siluroid Belodontichthys (pers. obs.). Acknowledgements I am greatly indebted to Dr P. Humphry Greenwood for his criticism of the manuscript and forhis many helpful suggestions that have aided my research. I am particularly grateful to Professor C. C. Lindsey for placing at my disposal the valuable(and, at that time, unpublished) observations he has made on the anatomy and behaviour ofChela, and to Dr P. Kahsbauer for locating and loaning to me the type specimen of Parachelabreitensteini. My most sincere thanks go to my colleagues, Drs P. J. P. Whitehead and K. E. Banister, fortheir many helpful criticisms and discussions; to Margaret Clarke for her assistance with thetaxonomic section of the paper, and to James Chambers for preparing alizarin specimens. Grateful thanks also go to Christopher Evans for his assistance with preparing the figures, toGina Sandford for typing the manuscript and for supplying specimens of Chela, and to DavidBird and the late Keith Purbrick for providing information on live Macrochirichthys. Finally, I must acknowledge the kindness of Dr Tyson Roberts who provided me with suchbeautiful specimens of Macrochirichthys from the Kapuas river together with photographs anddata concerning live specimens. References Alexander, R. McN. 1966. The functions and mechanisms of the protrusile upper jaw in two species ofcyprinid fish. /. Zoo/., Lond. 149 : 288-296. 1968. Animal mechanics. London. 1969. The orientation of muscle fibres in the myomeres of fishes. /. Mar. Biol. Assn. 49 : 263-289. Banarescu, P. 1963. Revision du genre Toxabramis Giinther (Pisces, Cyprinidae). Bull. Mus. natn Hist. Nat. (2), 35 (4) : 457-463. 1964. Revision du genre Pseudolaubuca, Bleeker 1864 = Parapelecus Gunther, 1889 (Pisces, Cyprinidae). Revue roum. Biol. Zool. 9 (2) : 75-86. 1967. Studies on the systematics of Cultrinae (Pisces, Cyprinidae) with description of a new genus. Revue roum. Biol. Zool. 12 (5) : 297-308. 19680. Revision of the Indo-Burmanese genus Salmostoma Swainson (Pisces, Cyprinidae) with description of a new subspecies. Revue roum. Biol. Zool. 13 (1) : 3-14. 19686. Revision of the genus Hemiculter (Pisces, Cyprinidae). Trav. Mus. Hist. not. 'Gr. Antipd" 8 : 523-529. 1968c. Remarks on the genus Chela Hamilton-Buchanan (Pisces, Cyprinidae) with description of a new subgenus. Anali Mus. civ. Stor. not. Giacomo Doria 78 ; 53-63. 1969. Contributions to the systematics of the genus Oxygaster (Pisces, Cyprinidae) with description of a new subspecies. Revue roum. Biol. Zool. 14 (1) : 191-198. 1970o. Contributions to the knowledge of the genus Megalobrama (Pisces, Cyprinidae). Revue roum. Biol. Zool. 15 (3) : 133-139. 19706. Remarks on the genus Xenocypris (Pisces, Cyprinidae) with description of a new subspecies. Revue roum. Biol. Zool. 15 (6) : 395-402. 197 la. Further studies on the systematics of Cultrinae with reidentification of 44 type specimens (Pisces, Cyprinidae). Revue roum. Biol. Zool. 16 (1) : 9-20. 19716. Revision of the genus Paralaubuca Bleeker (Pisces, Cyprinidae). Trav. Mus. Hist. not. 'Gr. An^pa" 11 : 347-355. 200 G. J. HOWES Basilewski, S. 1855. Ichthyographia Chinae Borealis (Pisces). Nouv. Mem. Soc. Imp. Nat. Mosc. 10 : 28-33.Berg, L. S. 1964. Freshwater fishes of the USSR and adjacent countries 2 (English translation of the 4th ed. of 1949), 496 pp. Bleeker, P. 1860. Ordo Cyprini, Karpers. Verh. natuurk. Ver. Ned. Ind. 7 : 1-492.Hr it Urn, M. R. 1954. A revision of the Indo-Malayan freshwater fish genus Rasbora. Manila, 224 pp.Brousseau, A. 1976. The pectoral anatomy of selected ostariophysi. II. TheCypriniformesandSiluriformes. J.Morph. 150:79-116.Dornesco, G. T. & Soresco, C. 1971 . Sur le development et la valeur morphologique de la region ethmoidale de la carpe. Anat. Anz. 129 : 33-52.Fowler, H. W. 1905. Some fishes from Borneo. Proc. Acad. not. Sci. Philad. 57 : 455-523. 1934. Zoological results of the third De Schaunense Siamese Expedition. Part 1 - Fishes. Proc. Acad. not. Sci. Philad. 86 : 67-163. 1935. Zoological results of the third De Schaunense Siamese Expedition. Part 6. Fishes obtained in 1934. Proc. Acad. nat. Sci. Philad. 87 : 89-163. 1937. Zoological results of the third De Schaunense Siamese Expedition. Part 8. Fishes obtained in 1936. Proc. Acad. nat. Sci. Philad. 89 : 125-264.Gosline, W. A. 1974. Certain lateral-line canals of the head in cyprinid fishes, with particular reference to the derivation of North American forms. Jap. J. Ichth. 21 (1) : 9-15.Greenwood, P. H., Rosen, D. E., Myers, G. S. & Weitzman, S. 1966. Phyletic studies of teleostean fishes, with a provisional classification of living forms. Bull. Am. Mus. nat. Hist. 131, Art. 4 : 339-456.Gunther, A. 1868. Catalogue of the fishes in the British Museum 7. London, 512 pp.Hora, S. L. 1923. On a collection offish from Siam. /. Siam. Soc. 6 : 143-184.Howes, G. J. 1976. The cranial musculature and taxonomy of characoid fishes of the tribes Cynodontini and Characini. Bull. Brit. Mus. nat. Hist. (Zool.) 29 (4) : 201-248. 1978. The anatomy and relationships of the cyprinid fish Luciobrama macrocephalus (Lacapede). Bull. Brit. Mus. nat. Hist. (Zool.) 34 (1) I 1-64. Jordan, D. S. 1919. The genera of fishes, Part 3. Leland Stanford Junior Univ. Pubs, University Series : 285-410 + i-xv.Lesiuk, T. P. & Lindsey, C. C. 1978. Morphological peculiarities in the neck-bending Amazonian characoid fish Rhaphiodon vulpinus. Can. J. Zool. 56 (4) pt 2 : 991-997.Lindsey, C. C. In press. Form, function, and locomotory habits in fish. In Fish Physiology (Ed. Hoar, W. S. & Randall, D. J.) 7 : 1-100.Menezes, N. A. 1976. On the Cynopotaminae, a new subfamily of Characidae (Osteichthys, Ostariophysi, Characoidei). Archos Zool. S. Paulo 28 (2) : 1-91. Mirza, M. R. 1975. Freshwater fishes and zoogeography of Pakistan. Bijdr. Dierk. 45 (20): 143-180.Mirza, M. R., Alam, M. & Kausar, R. 1974. A note on the osteology of the Cultrinae (Pisces, Cyprinidae) of Pakistan. Biologia 20 (2) : 181-182. Myers, G. S. 1940. The nomenclatural status of the Asiatic fish genus Culler. Copeia 1940 (3) : 199.Nichols, J. T. 1943. Freshwater fishes of China. Nat. Hist, of Central Asia 9. American Museum of Natural History, New York. 322 pp. Nikolsky, G. V. 1955. Special Ichthyology (English translation of 2nd edition, 1954), 538 pp.Patterson, C. 1975. The braincase of pholidophorid and leptolepid fishes, with a review of the actinoptery- gian braincase. Phil. Trans. R. Soc. Lond. B 269 (899) : 275-579.Rauther, M. 1950. Ober Pelecus cultratus (L.) in Vergleich mit anderen 'Beilfischen'. Zool. Anz. 145 : 794- 804.Silas, E. G. 1951. On a new cyprinid fish from Coorg, South India. /. Zool. Soc. India 3 (1) : 7-10. 1958. Studies on cyprinid fishes of the oriental genus Chela Hamilton. J. Bombay nat. Hist. Soc. 55(1): 54-99. Smith, H. M. 1945. The freshwater fishes of Siam, or Thailand. Bull. U.S. natn. Mus. 188 : 1-622. Steindachner, F. 1881. Ichthyologische Beitrage (XI). Sitz. Akad. Wiss. Wien 83 (1) : 393-408. Sorescu, C. 1968. Vergleichende Untersuchungen iiberden Schultergiirtel der Cyprinidae. Senk. biol. 49 (5) : 387-397. Taki, Y. 1974. Fishes of the Lao Mekong basin. U.S. Agency for International Development, Laos, 232 pp.Weber, M. & de Beaufort, L. F. 1916. The fishes of the Indo- Australian Archipelago. 3 Leiden, 455 pp.Weitzman, S. H. 1967. The origin of the stomiatoid fishes with comments on the classification of salmoni- form fishes. Copeia 1975 (3) : 507-540.Wu, H. W. 1939. On the fishes of Li-Kiang. Sinensia 10 (1-6) : 92-142. 1964. The Cyprinid Fishes of China 1. Shanghai, 228 pp. Manuscript accepted for publication 20 June 1978 British Museum (Natural History) Monographs & Handbooks Related titles (Zoology series Vol. 36 No. 3) The feeding mechanisms of a deep sea fishChauliodus sloani Schneider V. V. Tchernavin. 1953, viii+101 pp, 10 plates, 36 text figs. 4to paper. 3.85 The British Museum (Natural History) employs a staff of over 350research scientists working on zoology, entomology, palaeontology,botany and mineralogy. The results of their research in thesefields are published both in the Museum's scientific journals - theBulletins - and in monographs, many of which are co-publishedwith commercial scientific publishers. Many of these works arenot only of significance to such key areas as medicine, agricultureand the oil industry, but also to amateurs interested in birds,butterflies, fishes, etc. The Museum also publishes more popular books on natural historywhich are the work of their scientists and include a highillustrative content Lists are available free on request to: Publications Sales British Museum (Natural History) Cromwell Road London SW7 5BD Standing orders placed by educational institutions earn a discountof 10% off our published price. Titles to be published in Volume 36 A guide to the species of the genus Aspidisca.By Irene C. H. Wu & C. R. Curds. The Hemiuroidea : terminology, systematics and evolution.By D. I. Gibson & R. A. Bray. Notes on the anatomy of Macrochirichthys macrochirus(Valenciennes), 1844, with comments on the Cultrinae (Pisces,Cyprinidae). By G. J. Howes. Miscellanea Anatomy, relationships and classification of the familiesCitharinidae and Distichodontidae (Pisces, Characoidea).By R. P. Vari. Printed by Henry Ling Ltd, Dorchester Bulletin of the British Museum (Natural History) Miscellanea Zoology series Vol 36 No 4 25 October 1979 The Bulletin of the British Museum (Natural History), instituted in 1949, is issued in fourscientific series, Botany, Entomology, Geology (incorporating Mineralogy) and Zoology, andan Historical series. Papers in the Bulletin are primarily the results of research carried out on the unique andever-growing collections of the Museum, both by the scientific staff of the Museum and byspecialists from elsewhere who make use of the Museum's resources. Many of the papersare works of reference that will remain indispensable for years to come. Parts are published at irregular intervals as they become ready, each is complete in itself,available separately, and individually priced. Volumes contain about 300 pages and are notnecessarily completed within one calendar year. Subscriptions may be placed for one or moreseries. Subscriptions vary according to the contents of the Volume and are based on a forecastlist of titles. As each Volume nears completion, subscribers are informed of the cost of thenext Volume and invited to renew their subscriptions. Orders and enquiries should be sent to: Publications Sales, British Museum (Natural History),Cromwell Road, London SW7 5BD,England World List abbreviation: Bull. Br. Mus. nat. Hist. (Zool.) Trustees of the British Museum (Natural History), 1979 ISSN 0007-1498 Zoology series Vol 36 No 4 pp. 201-259British Museum (Natural History)Cromwell RoadLondon SW7 5BD Issued 25 October 1979 Miscellanea Contents Siliceous structures secreted by members of the subclass Lobosia (Rhizopodea :Protozoa). By C. G. Ogden 203 The first recorded specimens of the deep-water coral Lophelia pertusa (Linnaeus,1 758) from British Waters. By J. B. Wilson 209 The larval and post larval development of the brachyuran crab Geryon tridensKroyer (Family Geryonidae) reared in the laboratory. By R. W. Ingle . 217 Notes on the types of scorpions in the British Museum (Natural History),London. Buthus socotrensis Pocock, 1889 (Family : Buthidae). By M. Vachon 233 Five new prawn-associated gobies (Teleostei : Gobiidae) of the genus Amblye-leotris. By N. V. C. Polunin & R. Lubbock 239 The taxonomy of Procavia capensis in Ethiopia, with special reference to theaberrant tusks of P. c. capillosa Brauer (Mammalia, Hyracoidea). By G. B.Corbet 251 Siliceous structures secreted by members of thesubclass Lobosia (Rhizopodea : Protozoa) Colin G. Ogden Department of Zoology, British Museum (Natural History), Cromwell Road, London, SW7 5BD Introduction The need for a comprehensive taxonomic system for those amoebae with shells, usually referredto as testate amoebae, is long overdue. Nevertheless, before such a task is undertaken the validcriteria for each taxon should be established. The two main criteria used in recent classificationsof testate amoebae in the Superclass Rhizopodea are the cytoplasmic form of the pseudopodia andthe structure of the shell. The present study is concerned only with the latter, so the proposalsconcerning the mechanisms of pseudopodial movement suggested by Bovee & Jahn (1966) havenot been considered. Furthermore, the changes put forward here are modifications of theclassifications of Loeblich & Tappan (1961, 1964) and Deflandre (1953) -(referred to as the'legally-based system' by Bovee & Jahn). In these classifications the shape and composition of theshell has been used to determine the divisions at the superfamily and family level. Four basic typesof shell are recognized : first, the proteinaceous shell, usually composed of numerous alveoli;secondly, the agglutinate shell composed of extraneous material bound by an organic cement;thirdly, the siliceous shell usually composed of shell plates; and finally, the calcareous shellwhich may have an outer organic lining. The divisions proposed here relate to the third type of shell structure, and concern thoseanimals which make their own siliceous shell components. To date, that includes most of thespecies belonging to the subclass Filosia, and some species belonging to the subclass Lobosia,namely Difflugia oviformis Cash, 1909, Quadrulella symmetrica (Wallich, 1863) and Lesquereusiaspiralis (Ehrenberg, 1840). Other testate amoebae in the subclass Lobosia which have siliceousplates, for example, species belonging to the genera Nebela and Heleopera have agglutinate shells,made of captured shell plates or quartz particles. The shell plates of smaller testate amoebae,such as Euglypha, Assulina and Cyphoderia, are easily recognized in the shells of Nebela species,and MacK inlay (1936) suggested that these were obtained by predation after observing thatNebela collaris produced a membranous shell devoid of shell plates when grown in isolation. Discussion It is generally accepted that all testate amoebae secrete an organic material that either provides theentire shell, as in Arcella, or at least is used to cement the shell components together as in, forexample, Nebela, Difflugia and Euglypha. Fine structure studies (Hedley & Ogden, 1973, \914a;Netzel, 1975, \916a, 1977; Hedley et al, 1976, 1977) on species belonging to all four of the basicshell types have shown that this organic material is made in the Golgi complex of the cytoplasm,and have suggested how it is probably used in shell construction. In addition, the cytoplasmicchanges associated with the formation and distribution of siliceous structures in Euglypharotunda, E. acanthophora, E. strigosa, Trinema lineare and Difflugia oviformis have been describedin detail by Hedley & Ogden (1973, \974a, b) and Netzel (19766, 1977). These studies, based onlaboratory cultures, include observations on the biology of these species, and cine-films illus-trating binary fission have been made by Netzel (197 la, b). The siliceous structures secreted byEuglypha species and Difflugia oviformis are formed in a membrane-bound vesicle within thecytoplasm, and are stored there prior to division. At division, they are arranged around acytoplasmic extrusion to form a daughter shell identical to the parent. The term 'idiosomes' hasbeen suggested (Netzel, 1972) for the siliceous structures secreted by Difflugia oviformis. Bull. Br. Mus. nat. Hist. (Zool.) 36 (4) : 203-207 Issued 25 October 1979 203 204 C. G. OGDEN Using the diagnosis of the family Difflugiidae given by Loeblich & Tappan (1961, 1964), thatthe 'test is rarely chitinous, but is generally composed of foreign particles, not of secreted plates'and of the genus Difflugia- 'wall with pseudochitinous base and variable amounts of agglutinatematerial', it is apparent that Difflugia oviformis with its secreted shell does not agree with thisdefinition. There would appear to be no justification in amending the diagnosis for an alreadyovercrowded genus, instead it is proposed to create a new genus Netzelia to include D. oviformisand other species of Difflugia which secrete their own siliceous elements or idiosomes. A similar situation arises in the family Hyalospheniidae. The diagnosis for this family states -'test chitinous with siliceous plates or scales, rounded or angular, and may have foreign matteradded'. Two of the genera included in this family are thought to secrete a proteinaceous shell,Hyalosphenia Stein, 1857 and Leptochlamys West, 1901, and two siliceous structures, QuadrullellaCockerell, 1909 and Lesquereusia Schlumberger, 1845. An ultrastructural study of Hyalospheniapapilio by Joyon & Charret (1962) suggested that it had a proteinaceous shell, but little is knownabout the shell of Leptochlamys except that it was originally described as having a thin chitinousmembrane. Information on the shell of Quadrulelia is still needed, although it is assumed that itsecretes its own shell plates, because they have a distinct quadrangular shape (Fig. 1) which isrestricted to this genus and Paraquadrula Deflandre, 1932 which has calcareous plates. Speciesbelonging to Quadrulelia have previously been described as having calcareous, siliceous orchitinoid shells (Cash & Hopkinson, 1909 ; 134-135). Elemental analysis of whole shells of Q.symmetrica, recently carried out in this laboratory using an energy dispersive X-ray analyserattached to a scanning electron microscope, have shown that they are composed mainly ofsilicon, with some potassium and calcium present. The amounts detected suggest that the shellplates are siliceous and that the organic cement which binds them may be strengthened by theother elements. The genus Lesquereusia contains several species whose shells are composed mainlyof siliceous rods, three of these L. epistomum, L. modesta and L. spiralis have recently beenredescribed (Ogden & Hedley, 1980) and only L. modesta consistently incorporates irregularforeign particles amongst the rods in the shell. Although clonal cultures of Lesquereusia spiralis have not yet been established, observations ofthis species in isolation, in this laboratory, have shown that it secretes a daughter shell made ofcurved rods similar to those of the parent. Some of the laboratory specimens were smaller thanthose reported from the wild (see Ogden & Hedley, 1979), and this is thought to be due to adeficiency in the culture medium. A comparison between the curved rods of the smallest specimen,83 jim (Fig. 2) those of a medium specimen, 95 urn (Figs 4 & 5) and a large specimen, 120 um(Figs 6 & 7), show that these rods become more pronounced and areas of organic cement with thedistinctive pores (Fig. 3) less numerous with increase in size. Elemental analysis of whole shells,using an energy dispersive X-ray analyser, has shown that these rods are siliceous and suggeststhat the organic cement that binds them contains iron. The situation regarding the family Hyalospheniidae needs some clarification, but must awaitstudies on clonal cultures before this is possible. However, it seems to me that there are sufficientaffinities between Lesquereusia spiralis, Quadrulelia symmetrica and the new genus Netzelia to Fig. 1 Siliceous shell plates of Quadrulelia symmetrica. x 2400 Fig. 2 Shell surface of small specimen of Lesquereusia spiralis, to show the curved rods and pores. X 2100 Fig. 3 A higher magnification of the pores in the organic cement, from the area arrowed in Fig. 2. x 21 000 Fig. 4 A medium-sized specimen of L. spiralis to show the ill-defined siliceous rods. x 490 Fig. 5 Portion of shell surface of medium specimen, note the numerous pores. x 8900 Fig. 6 Large specimen of L. spiralis with well-defined siliceous rods. x 480 Fig. 7 Shell surface of large specimen, note the apparent absence of pores. x 4800 SILICEOUS STRUCTURES IN LOBOSIA 205 206 C. G. OGDEN warrant family status within the subclass Lobosia. I therefore propose to designate a family toaccommodate these species by redefining Lesquereusiidae Jung, 1942, previously synonymizedby Loeblich & Tappan (1961), to include those members of the subclass Lobosia which secretesiliceous elements. Family LESQUEREUSIIDAE Jung, 1942 nom. rev.[nom. correct pro Lecuereusiidae Jung, 1942] Shell constructed of siliceous rods, plates or idiosomes secreted in the cytoplasm, to whichmineral particles may be added; aperture circular, oval or elongate. Lesquereusia Schlumberger, 1845. Shell colourless, compressed ovoid or globose with asym-metrical neck, giving the appearance of a spiral, composed of interwoven siliceous rods andsometimes particles of quartz; aperture circular. to include: Lesquereusia epistomum Penard, 1902Lesquereusia modesta Rhumbler, 1895Lesquereusia spiralis (Ehrenberg, 1840) Netzelia gen. n. Shell colourless, ovoid, symmetrical, with a broad crown and sides taperingsmoothly to the aperture, composed of idiosomes but may incorporate grains of quartz; aperturecircular, with organic collar and often with four or five small lobes. to include: Netzelia oviformis (Cash, 1909) comb. n. Quadrulella Cockerell, 1909. Shell colourless, ovoid, composed of quadrangular shell platesarranged without overlapping; aperture oval. to include : Quadrulella symmetrica ( Wallich, 1 863). In defining the above taxonomic changes, none of the generic names proposed by Jung (1942)in his review of the genus Difflugia have been considered, I agree with Deflandre (1953) andsubsequent authors that these must be rejected as inadequate definitions. It is apparent from previous descriptions of species of Difflugia that problems have arisen inidentification due to differences of shell structure. For example, Penard (1902) described specimenssimilar to Difflugia tuberculata (Wallich, 1864) but having a thin, transparent shell without in-dentations. These specimens are listed by Jung (1942) as Cingodifflugia laevis (Penard, 1902).A species of Difflugia collected from water and mud in Alabama was tentatively identified byOwen & Jones (1976) as D. tuberculata. It produced autogenous siliceous components whenisolated in culture, and Owen & Jones suggested that this species should therefore be referred tothe genus Nebela. Their specimens do not agree with the accepted definition of D. tuberculata,which typically have distinctive tubercles of quartz grains on the shell surface (see Ogden &Hedley, 1979). However, this latter description may have to be amended because examination ofspecimens from the Everglades National Park, Florida, U.S.A. (kindly collected by Dr C. R.Curds, British Museum (Natural History)), suggest that D. tuberculata may occasionally constructa shell of diatom frustules instead of the usual quartz particles, both examples being presentin the sample. Nevertheless, I consider that the descriptions of Penard (1902), Jung (1942) andOwen & Jones (1976) all refer to specimens of Netzelia. It is probable that other smooth-shell species of Difflugia may secrete siliceous elements,although observations on such species in culture are needed. For example, the study of the shellstructure of Difflugia lobostoma given by Eckert & McGee-Russell (1974) must be consideredwith caution, as I believe from their description that these authors were studying specimens ofD. tuberculata. Nevertheless, the specimens examined were composed of a single layer of siliceousparticles held together by a network of cement, and dense granules similar in structure to thoseseen in Netzelia oviformis by Netzel (19766) were observed between the shell joints and in thecytoplasm. SILICEOUS STRUCTURES IN LOBOSIA 207 References Bovee, E. C. & Jahn, T. L. 1966. Mechanisms of movement in taxonomy of Sarcodina. III. Orders, suborders, families and subfamilies in the superorder Lobodia. Syst. Zool. 15 : 229-240.Cash, J. & Hopkinson, J. 1909. The British Freshwater Rhizopoda and Heliozoa. Vol. II Rhizopoda, part 2. The Ray Society, London 166 pp., 32 pis. Cockerell, T. D. A. 1909. Notes on Protozoa. Univ. Colo. Stud. gen. Ser. No. 6, 305-307.Deflandre, G. 1953. Ordres des Testacealobosa, Testaceafilosa, Thalamia ou Thecamoebiens (Rhizopoda, Testacea). In Traite de Zoologie. Vol. I. Fasc. II : 97-148. Paris.Eckert, B. S. & McGee-Russell, S. M. 1974. Shell structure in Difflugia lobostoma observed by scanning and transmission electron microscopy. Tissue Cell 6 : 215-221.Hedley, R. H. & Ogden, C. G. 1973. Biology and fine structure of Euglypha rotunda (Testacea : Protozoa). Bull. Br. Mus. nat. Hist. (Zool.) 25 : 119-137.1974. Observations on Trinema lineare Penard (Testacea : Protozoa). Bull. Br. Mus. nat. Hist. (Zool.) 26 : 187-199. 19746. Adhesion plaques associated with the production of a daughter cell in Euglypha (Testacea : Protozoa). Cell Tiss. Res. 153 : 261-268. & Mordan, N. J. 1976. Manganese in the shell of Centropyxis (Rhizopoda, Protozoa). Cell. Tiss. Res. Ill : 543-549. 1977. The biology and fine structure of Cryptodifflugia oviformis (Rhizopodea Protozoa). Bull. Br. Mus. nat. Hist. (Zool.) 30 : 311-328.Joyon, L. & Charret, R. 1962. Sur 1'ultrastructure de Thecamoebien Hyalosphenia papilio (Leidy). C.r. Acad. Sci. (Paris) 255 : 2661-2663.Jung, W. 1942. Siidchilenische Thekamoben (Aus dem sudchilensichen Kiistengebiet, Beitrag 10). Arch. Protistenk. 95 : 253-356. Leidy, J. 1874. Remarks on the American species of Difflugia. Proc. Acad. nat. Sci. Philad. 306-308Loeblich, A. R. & Tappan, H. 1961. Suprageneric classification of the Rhizopodea. /. Paleont. 35 : 245- 330.1964. Thecamoebians. In Treatise on Invertebrate Paleontology, Part C, Protists 2, Vol. 1, pp. C16-C54. The Geological Society of America, University of Kansas Press, Lawrence.MacKinlay, R. B. 1936. Observations on Nebela collar is Leidy (pro parte), a testate amoebae of moorland waters. Part 1. //. R. microsoc. Soc. 56 : 307-325.Netzel, H. 19710. Difflugia oviformis (Testacea) Bewegung und Fortpflanzung. Film E 1641 des Inst. Wiss, Film, Gottingen.19716. Euglypha rotunda (Testacea) Bewegung und Fortpflanzung. Film E 1642 des Inst. Wiss. Film, Gottingen. 1972. Die Schalenbildung bei Difflugia oviformis (Rhizopoda, Testacea). Z. Zellforsch. 135 : 55-61. 1975. Die Entstehung der hexagonalen Schalenstruktur bei der Thekamobe Arcella vulgar is var. multinucleata (Rhizopoda, Testacea). Arch. Protistenk. 117 : 321-357. \916a. Die Abscheidung der Gehausewand bei Centropyxis discoides (Rhizopoda, Testacea). Arch. Protistenk. 118 : 53-91.19766. Die Ultrastruktur der Schale von Difflugia oviformis (Rhizopoda, Testacea). Arch. Protistenk. 118 : 321-339. 1977. Die Bildung des Gehauses bei Difflugia oviformis (Rhizopoda, Testacea). Arch. Protistenk. 119 : 1-30. Ogden, C. G. & Hedley, R. H. 1980. An Atlas of Freshwater Testate Amoebae. British Museum (Natural History).Owen, G. & Jones, E. E. 1976. Nebela tuberculata comb. nov. (Arcellinida), its history and ultrastructure. /. Protozoa!. 23 : 485-487.Penard, E. 1902. Faune Rhizopodique du Bassin du Leman. Geneva, 700 pp. Manuscript accepted for publication 16 August 1978 The first recorded specimens of the deep-watercoral Lophelia pertusa (Linnaeus, 1758) fromBritish waters J. B. Wilson Institute of Oceanographic Sciences, Wormley, Godalming, Surrey GU8 SUB Synopsis Recognition of the deep-water coral Lophelia pertusa (Linnaeus, 1758) as part of the British fauna wasbased on four early nineteenth century specimens from Scottish waters, two from the Shetlands and twofrom the Inner Hebrides. These specimens have now been located and are figured. Each supports someepizoic remains including bryozoans, serpulid polychaetes, cirripedes and bivalves. Introduction During the early nineteenth century four specimens of the deep-water coral Lophelia pertusa(Linnaeus, 1758) were obtained by fishermen from Scottish waters. Two were from off the ShetlandIslands and two from the Inner Hebrides. The specimens were mentioned by Johnston (1847) inthe second edition of his work and later by Gosse (1860). They are important in that they are theearliest records of Lophelia from British waters. Following Zibrowius (1976), the combination Lophelia pertusa (L.) will be used in this paper.The specimens were referred to as Oculina prolifera by Johnston (1847) and as Lophohelia pro-lifera by Gosse (1860). The Shetland specimens The precise collecting localities for the two Shetland specimens are not known. Lophelia does,however, occur on the edge of the Continental Shelf and the upper Continental Slope to the westand north of the Shetland Islands at depths of 190 m to approximately 300 m (Wilson, 1979a). One specimen, perhaps the earliest recorded in British waters, was obtained by George C.Atkinson, possibly during a visit to Shetland in 1832 (Atkinson, 1838 : 223). He presented it tothe then Newcastle Natural History Society (now, after several name changes, the NaturalHistory Society of Northumbria) and it was placed in the Newcastle Museum (now the HancockMuseum, part of the University of Newcastle upon Tyne) (Johnston, 1847 : 252) in 1834 or1835 (Natural History Society of Northumberland, 1838 : 423). The coral collection in the Hancock Museum was examined by the author in 1974 and found toinclude only one specimen of Lophelia (PI. 1A). The specimen was unlabelled. It is reasonable toassume that it is Atkinson's Shetland specimen, however, as it is 220 mm wide and 260 mm long.It can therefore be reconciled with the brief description given to Johnston by Joshua Alder that'the specimen is eight or ten inches across' although dimensions alone clearly cannot positivelyidentify the specimen. It weighs 2-1 kg. This specimen shows the point of attachment to the substrate, and also records the early growthof the colony (Wilson, 19796). The initial attachment was probably to an outcrop or largeboulder and subsequent growth incorporated several adjacent small pebbles (PI. 1A). Considera-tion of the form of the colony and the relative positions of the small pebbles on the sedimentsurface has enabled its probable orientation on the sea floor to be reconstructed (Fig. 1). The specimen is clean in appearance and is largely free from epizoids over parts of its surfaceimplying that it was partly covered by living tissue when collected. Evidence of attack by clionid Bull. Br. Mus. not. Hist. (Zool.) 36 (4) : 209-215 Issued 25 October 1979 209 210 J. B. WILSON Fig. 1 Reconstruction of the probable orientation of the colony of Lophelia pertusa, in the HancockMuseum collection, on the sea floor. The initial attachment was probably to a large boulder or rockoutcrop on the left. Subsequent lateral growth of the colony took place towards the right overthe adjacent small pebbles on the sediment surface which became incorporated in the colony. Twoof the four pebbles incorporated in this way (see PI. 1 A) are visible. sponges is restricted to the 20-30 mm closest to the original point of attachment. Breakage didnot occur above the point of attachment during collection because that part of the colony was onlyslightly weakened by the sponge borings. The specimen is therefore complete. The epifauna included the bryozoans Pyripora catenularia (Fleming), Amphiblestrum flemingii(Busk), Schizomavella sp., Sertella sp., cf. Oncousoecia dilatans (Johnston), Plagioecia patina(Lamarck), Diplosolen obelium (Johnston) and Disporella hispida (Fleming); the barnacle Verrucastroemia (Miiller); the polychaetes Serpula vermicularis (L.) and Filogrania sp. and the bivalvesHeteranomia sp. and Hiatella sp. The other Shetland Lophelia was 'a very large specimen' (Johnston, 1847) obtained from Unstfishermen by Dr Laurence Edmonston, the Shetland naturalist, and given to J. Gwyn Jeffreys,who in turn presented it to the British Museum (Norman, 1869). Johnston was told of this speci-men by Edward Forbes who, like Jeffreys, was a correspondent of Edmonston (Blaikie, 1888).Jeffreys visited Shetland in 1841 (Harrison, 1892) and it is possible that he was given the specimenthen. Plate 1 Specimens of Lophelia pertusa from off Shetland. (A) Specimen probably obtained by George C. Atkinson and presented to the Newcastle NaturalHistory Society. Hancock Museum collections. The pebbles covered by lateral growth of thecolony are on the bottom left side of the specimen. Scale =50 mm. (B) Specimen (now in two pieces) obtained by Dr Laurence Edmonston from Unst fishermen andgiven to J. Gwyn Jeffreys. British Museum (Natural History) collections Reg. No. 1864.9.1.6.Note the clionid sponge borings on the bottom part of the right-hand portion. Scale = 50 mm. 212 J. B. WILSON A specimen of L. pertusa from Shetland presented by Jeffreys was registered in the BritishMuseum collections in 1864 (BMNH Reg. No. 1864.9.1.6). As this is the only specimen in thecollection from Shetland which was presented by Jeffreys it is probably Edmonston's specimen.It weighed 0-58 kg, and measured 260 mm by 140 mm. The specimen was broken many yearsago and now exists as two pieces of approximately equal size (PI. IB). The specimen incorporates several eunicid polychaete tubes and displays a fairly open growthform. The individual corallites at the extremities of growth are quite large, most being 15-17 mmin diameter. Parts of the specimen had been extensively bored by clionid sponges (PI. IB). Thecolony supported an epifauna including Serpula vermicularis and large colonies of the bryozoanTurbicellepora sp. One of the latter had a young colony of Anarthropora monodon Busk growing onit while another partially surrounds a Serpula tube. Boring Bryozoa were also present. Although parts of the specimen are free from epifauna, the overall appearance suggests that thecoral was dead when collected. The Inner Hebridean specimens Fleming (1846) recorded a specimen 2-72 kg ('6 Ibs') in weight brought up by fishermen from theSound of Rhum, between the islands of Rhum and Eigg, Inner Hebrides in 1845. Water depthsof up to 160 m are to be found at the south-western end of the Sound. This specimen was exhibitedat a meeting of the Royal Society of Edinburgh in 1846 and was referred to in a footnote inJohnston (1847 : 251-252). Gosse (1860), who was also told of this specimen by Professor G.Dickie, recorded it as having been deposited by Fleming in the Museum of King's College,Aberdeen. Ritchie (1912) considered that the specimen perhaps still existed as an unlabelledspecimen in the Natural History Museum at Marischal College, Aberdeen. The British Museum(Natural History) collections contain a small specimen presented by Fleming, 9-6 g in weight(BMNH Reg. No. 1849.9.21.4) labelled: 'This is a fragment of the specimen "exhibited" by Dr Fleming at a meeting of the RoyalSoc. of Edinr. 2nd March 1846, "6 pounds in weight, which was found last summer byfishermen, their lines having become entangled with it in the sea between the Islands ofRum and Egg" [sic] - Brit. Zooph. 252 - Presented by Dr Fleming.' This small piece (PI. 2A) was clearly broken off the large specimen sometime between 1845(the year of collection) and 1849 (the year of accession to the British Museum). A large unlabelledspecimen of Lophelia weighing 2-48 kg (5 Ib 7 oz.), examined by the author in the University ofAberdeen Natural History Museum collections in 1977 (Reg. No. Coel 189 Z2A) was thoughtperhaps to be the missing Sound of Rhum specimen. That this specimen is in fact the one exhibitedby Fleming and referred to by Gosse has now been proved by reuniting the small piece in theBritish Museum (Natural History) collection to the point on the larger specimen from where ithad been broken off (PI. 2A). The larger piece supported an epifauna including Serpula vermicularis, Hydroides sp., Verrucastroemia and bivalves including cf. Heteranomia sp., Kellia suborbicularis (Montagu) and Hiatellasp. Three species of Bryozoa - Amphiblestrum flemingii (Busk), Porella concinna (Busk) andPlagioecia patina (Lamarck) - were also fairly common, mostly as young colonies which haddeveloped brooding structures. Boring Bryozoa were also present. Parts of the specimen hadbeen extensively bored by clionids. The growth form of the colony is very compact (PI. 2A), in marked contrast to that of theEdmonston/Jeffreys specimen from Shetland. The individual corallites are also much smaller. The small piece in the British Museum (Natural History) collections still has orange-pinkcoloration and has traces of dried tissue in the calices. Parts of the larger piece, particularly closeto the point where the small piece was broken off, are clean in appearance, indicating that parts ofthis specimen were undoubtedly alive at the time of collection. Gosse (1860) recorded and figured (pi. X) a specimen obtained by fishermen in deep water offSkye in 1852 and presented to Dickie. This specimen (PI. 2B), which weighs 0-99 kg, was given in Plate 2 Specimens of Lophelia pertusa from the Inner Hebrides. (A) Specimen obtained by fishermen from Sound of Rhum in 1845 and exhibited by ProfessorJ. Fleming in 1846. The small piece in the top left-hand corner was broken off from the pointindicated by the arrow and presented to the British Museum BMNH Reg. No. 1849.9.21.4. Thelarge piece is in the University of Aberdeen Natural History Museum collections Reg. No. Coel189Z2A. Scale = 50 mm. (B) Specimen obtained by fishermen from off Skye in 1852 and given to Professor G. Dickie.National Museum of Ireland collections. Arrow indicates prominent Caberea ellisii colony. Thecoral is extensively bored by clionid sponges. Scale =50 mm. 214 J. B. WILSON 1869 by Dickie to A. G. More who was then an Assistant in the National Museum of Ireland,Dublin, and placed by him in the Museum collection (J. M. C. Holmes, personal communication).It is recorded as having been obtained 1 1 km (6 miles) west of Skye. Water of 145-190 m depthoccurs in the Little Minch, 1 1 km west of Dunvegan Head, Skye, and it is possible that thespecimen came from there. Lophelia was not recorded, however, during the British Associationdredging investigations off Skye (Jeffreys, 1867; Norman, 1867). This specimen supported a rich epifauna including Serpula vermicular is, Hydroides sp., Verrucastroemia, Heteranomia sp., Modiolus phaseolinus (Philippi), Hiatella sp. and Crania anomala(Miiller). The bryozoan fauna was particularly rich and included Amphiblestrum flemingii (Busk),Caberea ellisi (Fleming) (see PI. 2B), Escharella ventricosa (Hassall), Schizomavella linearis(Hassall), Smittoidea reticulata (J. Macgillivray), Turbicellepora sp., Sertella sp., Stomatopora cf.trahens (Couch), Diplosolen obelium (Johnston), Disporella hispida (Fleming) and Lichenoporacf. radiata (Audouin). All the bryozoan colonies were small and some may have been only a few weeks old when thespecimen was collected. A high proportion of these species had developed brooding structures. The specimen also shows a compact growth form comparable with that of the Flemingspecimen. It was extensively bored by clionid sponges. The remaining skeleton of the coral isgrey in colour (see Gosse, pi. X) and was almost certainly completely dead when collected. Recognition of L. pertusa as part of the British fauna L. pertusa was not listed by Fleming (1828) or by Johnston (1838) in the first edition of his work.By the second edition (1847), Johnston knew of the two Shetland specimens and of Fleming'sspecimen and he suggested that L. pertusa should be included in the British fauna. It was notincluded by Forbes (1851) in his compilation of the early results of the British AssociationDredging Committee investigations, although the section of this report dealing with the 'Zoo-phyta' (pp. 245-246) was based on records given by Johnston (1847). By 1860, however, Gosse was able to figure Dickie's specimen in addition to recording theFleming and Edmonston specimens and therefore to recognize L. pertusa as undoubtedly part ofthe British fauna. Gosse apparently did not make use of the footnote in Johnston (1847 : 251-252)as the important Atkinson specimen was not mentioned. Further recognition of the species as British came when McAndrew (1861), using Gosse's data,included L. pertusa (as Oculina prolifera) in his check list of the British marine invertebrate faunaprepared for the Dredging Committee of the British Association, and subsequent authors haveaccepted it without comment. Acknowledgements The British Museum (Natural History), London, the Hancock Museum, University of Newcastleupon Tyne, the National Museum of Ireland, Dublin and the Natural History Museum, Universityof Aberdeen are thanked for the loan of specimens described in this paper. Drs P. F. S. Cornelius,F. Evans, R. S. Thorpe, Messrs F. St P. D. Bunker, J. M. C. Holmes, A. P. Nimmo, K. R. Watt,Mrs A. Datta and Miss A. A. Kirkpatrick are thanked for their assistance in the search for thespecimens and for details of their accession to the various museum collections. Miss P. L. Cook is thanked for identifying and commenting on the Bryozoa. The specimenswere photographed by Mr A. F. Madgwick. The fine illustration of the Hancock Museum speci-men (Fig. 1) was drawn by Miss P. E. Williamson. Miss J. M. Tidy is thanked for assistance during the study of the specimens and for theidentification of some of the epifauna. Drs P. F. S. Cornelius and A. L. Rice are thanked forcommenting on the manuscript. References Atkinson, G. C. 1838. A notice of the island of St Kilda on the north-west coast of Scotland. Trans,not. Hist. Soc. Nor thumb. 2 : 215-225. DEEP-WATER CORAL LOP H ELI A PERTUSA 215 Blaikie, W. G. 1888. Edmonston, Laurence, M.D. (1795-1879). In Stephen, L. (editor) Dictionary ofnational biography volume 16, Drant-Edridge, p. 397. London. Fleming, J. 1828. A history of British animals, exhibiting the descriptive characters and systematical arrange-ment of the genera and species of quadrupeds, birds, reptiles, fishes, Mollusca, and Radiata of the UnitedKingdom. Edinburgh. 1846. On the recent Scottish madrepores with remarks on the climatic character of the extinct races. [Report of specimen exhibited at meeting 2nd March 1846.] Proc. R. Soc. Edinb. 2 : 82-83, andEdinb. phil. J. 41 : 203-204. Forbes, E. 1851. Report on the investigation of British marine zoology by means of the dredge. Part I.The infra-littoral distribution of marine Invertebrata on the southern, western and northern coastsof Great Britain. Rep. Br. Ass. Advmt Sci. (Edinburgh 1850) : 192-263. Gosse, P. H. 1860. Actinologica Britannica. A History of the British Sea-Anenomes and Corals. London. Harrison, W. J. 1892. Jeffreys, John Gwyn (1809-1885). In Lee, S. (editor) Dictionary of national bio-graphy volume 29, Inglis-John, pp. 284-285. London. Jeffreys, J. G. 1867. Report on dredging among the Hebrides. Rep. Br. Ass. Advmt Sci. (Nottingham1866) : 186-193. Johnston, G. 1838. A History of the British Zoophytes. Edinburgh. 1847. A History of the British Zoophytes. 2nd ed. 2 vols. London. McAndrew, R. 1861. List of the British marine invertebrate fauna [for the Dredging Committee of theBritish Association]. Rep. Br. Ass. Advmt Sci. (Oxford 1860) : 217-236. Natural History Society of Northumberland, 1838. List of presents, from August, 1831, to December 1837.Trans, nat. Hist. Soc. Northumb. 2 : 414-432. Norman A. M. 1867. Report of the Committee appointed for the purpose of exploring the coasts of theHebrides by means of the Dredge. Part II. On the Crustacea, Echinodermata, Polyzoa, Actinoza,and Hydrozoa. Rep. Br. Ass. Advmt. Sci. (Nottingham 1866); 193-206. Norman, A. M. 1869. Shetland final dredging report. Part II. On the Crustacea, Echinodermata, Polyzoa,Actinozoa and Hydrozoa. Rep. Br. Ass. Advmt Sci. (Norwich 1868) : 247-342. Ritchie, J. 1912. Two rare corals, and polyzoa from Rockall. Scott. Nat. (1912) : 281. Wilson, J. B. \919a. The distribution of the coral Lophelia pertusa (L.) [L. prolifera (Pallas)] in the north-east Atlantic. /. mar. biol. Ass. U.K. 59 : 149-164. 19796. 'Patch' development of the deep-water coral Lophelia pertusa (L.) on Rockall Bank. /. mar. biol. Ass. U.K. 59 : 165-177. Zibrowius, H. 1976. Les scleractinaires de la Mediterranee et de V Atlantique nord-oriental. Unpublishedthesis. Univ. d'Aix-Marseille. Manuscript accepted for publication 30 October 1978 The larval and post-larval development of thebrachyuran crab Geryon tridens Kroyer (FamilyGeryonidae) reared in the laboratory R.W. Ingle Department of Zoology, British Museum (Natural History), Cromwell Road, London SW7 5BD Synopsis Four zoeal stages, a megalopal and first crab stage of the N.E. Atlantic crab Geryon tridens are describedfrom laboratory reared material and compared with the corresponding stages of the N.W. AtlanticG. quinquedens. Diagnostic features are given for distinguishing the zoeae and megalopa of G. tridensfrom those of the portunid crabs and from Goneplax rhomboides occurring in British waters. The juvenilecrab stages of G. tridens are compared with those of the southern Atlantic deep water G. longipes. Thedevelopmental stages of G. tridens suggest that Geryon evolved from the same phylogenetic stock as thePortunidae, Xanthidae and perhaps a part of the Goneplacidae. Introduction The crab Geryon tridens Kroyer has been recorded from the waters of northern Scandinavia, thenorthern North Sea and the N.E. Atlantic Ocean to just south of Ireland (Christiansen, 1969 :85-86 and BM (NH) records). Further southward its distribution is uncertain as some authorities(Bouvier, 1940 : 269) have synonymized G. tridens with the southern G. longipes A. MilneEdwards, while Zariquiey Alvarez (1968 : 389) has maintained G. longipes as a valid species. Only the pre-zoea and first zoea of G. tridens have been described previously fromlaboratory hatched specimens of a female collected south of Bergen, Norway (Brattegard &Sankarankutty, 1967). In April 1975 an ovigerous G. tridens was trawled in the North Sea andpresented to the BM(NH) by Dr M. S. Rolfe. The hatched larvae were successfully reared toprovide material for the following description of the complete larval development of this species. Materials and Methods The ovigerous specimen was taken in the Auk oil field region, about 1 50 miles off the Firth ofForth, between 5620-1' N : 0207' W and 5624-0' N : 0204' W, in an 8 m beam trawl workedat 85 m from the MAFF R.V. Corella. The female and reared material are deposited in theCollections of the Zoology Department, BM(NH), reg. nos 1976 : 4; 1978 : 176-189. The larvae were reared using the methods described by Rice & Ingle (1975 : 104) and Ingle &Clark (1977). All material was fixed and stored in the preservative formulated by Steedman(1976 : 148) until studies had been completed and then transferred to 70% ethanol for permanentstorage. Drawings and measurements were made with the aid of a camera lucida and somemorphological details were confirmed by scanning electron microscopy. Measurements takenwere: (a) the distance between tips of dorsal and rostral spines (T.T.), (b) carapace length from betweenthe eyes to the posterio-lateral carapace margin (C.L.). Results Hatching occurred between 5 and 6 May 1975; an average of 69 days elapsed between hatchingand the appearance of first crab stages. A percentage of the hatch reached seventh and one Bull. Br. Mus. not. Hist. (Zool.) 36 (4) : 217-232 Issued 25 October 1979 217 218 R. W. INGLE Fig. 1 Geryon tridens: zoeal stages (a) I, c.l. = 0-9 mm; (b) II, c.l. = 1-2 mm; (c) III, c.l. = 1-5 mm;(d) IV, c.l. = 2-0 mm. specimen eighth, crab stage but further development was prevented by a failure of the airconditioning system. Successfully reared larvae hatched as free swimming zoeae. Attempts were made to rearprezoeae liberated during the initial stages of hatching, but only one succeeded in developing tofirst zoea. Descriptions Geryon tridens Kroyer, 1837 Larval references: Geryon tridens Brattegard & Sankarankutty, 1967 : 7-12, figs 1-3 (prezoea,1st zoea). First zoea DIMENSIONS. T.T. 2-6-2-8 mm; C.L. 0-8-0-9 mm. LARVAL DEVELOPMENT OF GER YON TRIDENS 219 Fig. 2 Geryon tridens: abdomens of zoeal stages I-IV, dorsal (a), (c), (e), (g) and lateral (b), (d),(f), (h) aspects. Frontal aspects of (i) zoea I, (j) zoea IV. Scale = 0-5 mm, inset of (g) = 0-1 mm. CARAPACE (Figs la, 2i). Dorsal spine well developed, straight, narrowing distally. Rostral spinestraight, lateral spines long. Dorso-median elevation prominent. A pair of small dorso-lateralsetae near base of dorsal spine. Posterio-lateral margin of carapace with a row of short spinules. EYES. Partly fused to carapace. ANTENNULE (Fig. 3a). Unsegmented, with two terminal aesthetascs and two short setae. ANTENNA (Fig. 3f). Distal |-f of spinous process spinulate; exopod not reaching into distalhalf of spinous process, with 2 terminal spines; endopod not developed. MANDIBLE (Fig. 3k). Incisor and molar processes well developed, palp absent. MAXILLULE (Fig. 4a). Endopod 2-segmented with 1, 6 setae respectively; basal endite with 4setose spines and 2 setae; coxal endite with 9 setae. MAXILLA (Fig. 5a). Endopod with large outer and small inner lobe with 5 + 3 setae; basal 220 R. W. INGLE Fig. 3 Geryon tridens: antennules (a)-(d) of zoeae I-IV and (e) of megalopa. Antennae (f)-(i) ofzoeae I-IV and (j) of megalopa. Mandibles (k) of zoeae I, (1) of zoea IV from ventral aspect and(m) of megalopa from dorsal aspect. Scales = 0-1 mm. endite with large outer and small inner lobe with 6 + 5 setae; coxal endite bilobed with 4 + 3setae; scaphognathite with 8 marginal setae and one long plumose posterior projection. FIRST MAXILLIPED (Fig. 6a). Basis with 9-10 setae (arranged 2, 2, 3, 3); endopod 5-segmentedwith 2, 2, 1, 2, 4+ 1 setae; exopod incipiently 2-segmented with 4 terminal natatory setae. SECOND MAXILLIPED (Fig. 7a). Basis with 4 setae; endopod 3-segmented with 1, 1, 5 setae;exopod incipiently 2-segmented with 4 terminal natatory setae. THIRD MAXILLIPED AND PEREIOPODS. Represented as unsegmented buds. ABDOMEN (Fig. 2a, b). 5-segmented + telson; 2nd segment with a pair of outwardly directeddorso-lateral processes; 3rd segment with a pair of smaller posteriorly curved dorso-lateralprocesses; 4th segment with a small pair of dorso-lateral spines. Posterio-lateral processes of LARVAL DEVELOPMENT OF GERYON TRIDENS 221 3rd to 5th segments decreasing in size on successive segments. A pair of minute setae near posterio-dorsal margin of each segment. Telson forks long, diverging posteriorly, with one long and onesmall lateral spine, dorsal spine well developed. Inner posterior margin of telson convex nd with3 pairs of long setae, innermost pair with long setules in middle section. Second zoea DIMENSIONS. T.T. 3-4-3-6 mm; C.L. 1-2-1-3 mm. Fig. 4 Geryon tridens: maxillules (a)-(d) of zoeae I-IV and (e) of megalopa. Scale = 0-1 mm, insetto (a) = 0-03 mm. CARAPACE (Fig. Ib). Considerably elevated in cross-section; dorsal spine sometimes with minutespinules; posterio-lateral margin with much longer spinules than in first stage. EYES. Now stalked. ANTENNULE (Fig. 3b). With 6 aesthetascs. ANTENNA (Fig. 3g). Longer of the terminal spines on exopod much longer than in first stage :endopod bud well developed. MANDIBLE. Unchanged. MAXILLULE (Fig. 4b). Outer margin of basal endite with a prominent plumose seta, distal marginwith 6 setose spines and 5 setae; coxal endite with 10-11 setae. MAXILLA (Fig. 5b). Basal endite with 7 + 7 setae; coxal endite with 4 + 4 setae; scaphognathitewith 18 marginal setae. FIRST MAXILLIPED (Fig. 6b). Exopod with 9-10 terminal natatory setae. SECOND MAXILLIPED (Fig. 7b). Distal segment of endopod with 6 setae; exopod with 9-10terminal natatory setae. 222 R. W. INGLE Fig. 5 Geryon tridens: maxillae (a)-(d) of zoeae I-IV and (e) of megalopa. Scale = 0-1 mm. THIRD MAXILLIPED AND PEREIOPODS. Unsegmented buds larger than those of first stage. ABDOMEN (Fig. 2c, d). Posterio-lateral processes longer than those in first stage. Inner marginof telson with 4 pairs of setae, innermost pair small. Third zoea DIMENSIONS. T.T. 4-0-4-2 mm; C.L. 1-5-1-6 mm. CARAPACE (Fig. Ic). Dorsal spine stouter than in 2nd stage; setules prominent when present. EYES Unchanged. ANTENNULE (Fig. 3c). Setation unchanged. ANTENNA (Fig. 3h). Exopod reaching into distal half of spinous process; endopod bud muchlonger than in 2nd stage. LARVAL DEVELOPMENT OF GER YON TRIDENS 223 Fig. 6 Geryon tridens: 1st maxilipeds of (a)-(d) zoeae I-IV and (e) of megalopa. Scales = 0-2 mmexcept inset to (e) = 0-1 mm. MANDIBLE. Incisor and molar processes broader and serrate. MAXILLULE (Fig. 4c). Basal endite with 12 setae; coxal endite with 12-13 setae. MAXILLA (Fig. 5c). Basal endite with 8 + 8 setae; coxal endite with 4 + 6 setae; scaphognathitewith 25-29 setae. FIRST MAXILLIPED (Fig. 6c). Coxa with prominent epipod; endopod distal segment with 5+1setae; exopod with 12-14 terminal natatory setae. SECOND MAXILLIPED (Fig. 7c). Coxa with epipod; exopod with 12-14 terminal natatory setae.THIRD MAXILLIPED AND PEREIOPODS. Buds larger than those of 2nd stage. ABDOMEN (Fig. 2e, f). 6-segmented; posterio-lateral processes, particularly of 4th-5th segments,longer than in 2nd stage. Pleopod buds developed, vestigial on 6th segment. Inner margin oftelson with 5 pairs of setae (but sometimes with 6 setae on one side and 5 on other). 224 R. W. INGLE Fig. 7 Geryon tridens : 2nd maxillipeds of (a)-(d) zoeae I-I V and (e) of megalopa ; (f ) 3rd maxillipedof megalopa. Scales = 0-2 mm except insets to (a) and (b) = 0-1 mm. Fourth zoea DIMENSIONS. T.T. 4-9-5-2 mm; C.L. 1-8-2-0 mm. CARAPACE (Figs Id, 2j). Lateral spines slightly shorter than in 3rd stage. EYES. Unchanged. ANTENNULE (Fig. 3d). With 1 1 aesthetascs and 3 setae; endopod developed as a bud. ANTENNA (Fig. 3i). Exopod reaching well into distal half of spinous process; endopod un-segmented, almost as long as spinous process and with a terminal seta. MANDIBLE (Fig. 31). With an unsegmented palp. MAXILLULE (Fig. 4d). Basal endite with 18 setae; coxal endite with 17 setae. LARVAL DEVELOPMENT OF GERYON TRIDENS 225 Fig. 8 Geryon tridens: megalopa (a)-(e) 1st to 5th pereiopods, scale = 0-5 mm, inset to (e) = 0-3mm; (f) subterminal setae on dactylus of 5th pereiopod, scale 0-05 mm; (g) 1st pleopod, scale= 0-3 mm, inset, scale 0-05 mm; (h) telson and uropods, ventral aspect, scale = 0-1 mm; (i)abdomen, lateral aspect, scale = 0-5 mm; dorsal aspects of (j) megalopa c.l. = 3-0 mm and (k) 1stcrab stage c.l. = 3-0 mm. MAXILLA (Fig. 5d). Basal endite with 11 + 10 setae; coxal endite with 5 + 8 setae; scaphognathitewith 40-42 setae. FIRST MAXILLIPED (Fig. 6d). Coxal epipod longer than in 3rd stage; exopod with 16-17 terminalnatatory setae. SECOND MAXILLIPED (Fig. 7d). Coxal epipod larger than in 3rd stage; exopod with 17-18 terminalnatatory setae. THIRD MAXILLIPEDS. With a well developed exopod and 2 gill buds.PEREIOPODS. Incipiently segmented, first pair chelate. 226 R. W. INGLE ABDOMEN (Fig. 2g, h). Smaller of 2 lateral spines on telson very reduced. Pleopod buds longerthan in 3rd stage. Inner margin of telson with 6 pairs of setae. Megalopa DIMENSIONS. C.L. 3-0-3-1 mm. CARAPACE (Fig. 8j) Longer than broad, narrowing anteriorly. Frontal region with a deep medianfurrow, rostrum deflected ventrally; each protogastric and inner epibranchial region with asmall swelling; mesogastric region depressed; cardiac with a narrow and a broad U-shapedcarina and one anteriorly placed tubercle on either side; intestinal region with a minute mediantubercle. EYES. Large and long, with well-developed cornea. ANTENNULE (Fig. 3e). Peduncle 3-segmented, 1st segment with a row of transversely placedsetae; 2nd segment with 3 disto-internal setae; exopod 4-segmented, 2nd segment with 6, 3rdwith 10 aesthetascs and 2 setae respectively, 4th segment with 2 terminal setae; endopod segmentwith 4 terminal and 1 sub-terminal setae. ANTENNA (Fig. 3j). Peduncle 3-segmented, 3rd segment with 2 long setae, flagellum 8-segmented,3rd segment with 2 setae, 5th segment with 2 long and 1 short setae, 6th-7th segments with 2 and3 setae respectively, 8th segment with 4 terminal aesthetascs. MANDIBLE (Fig. 3m). Incisor process expanded as a broad concave plate with a sharp curvedmargin, molar process reduced; mandibular palp stout 2-segmented, proximal segment longerthan distal with 1 disto-external setae, distal segment with 13-15 setae. MAXILLULE (Fig. 4e). Endopod reduced but still with 6 setae; basal endite with 14 spines and12-13 setae; coxal endite still with 17 setae. MAXILLA (Fig. 5e). Endopod reduced, at the most with 2 outer basal setae; basal endite with11+8 setae; coxal endite with 6+13-14 setae; scaphognathite with 62-63 setae. FIRST MAXILLIPED (Fig. 6e). Exopod 2-segmented, proximal segment with 5 disto-external setae,distal segment with 3 terminal setae; basis with a longitudinal row of 23-25 marginal setae and afurther row of 8-9 setae near inner margin of ventral surface; endopod indistinctly 2-segmented,terminally sub-acute with 3 setae on inner proximal margin and 4 setae on disto-outer margin;epipod well developed and with 10-12 setae. SECOND MAXILLIPED (Fig. 7e). Coxa with 2-3 setae on inner margin; endopod 4-segmented, basalsegment (merus) longest and with 5 small marginal setae, 3rd segment (propodus) with 2 spinesand 6 setae, 4th segment (dactylus) with 7 spines and 1 seta; exopod 2-segmented, distal segmentwith 4 terminal setae; epipod bifurcate, longer and thinner part of bifurcation with several sub-terminal setae. THIRD MAXILLIPED (Fig. 7f). Coxa/basis with a transverse row of setae; ischium inner marginwith 17-25 setae, outer margin of merus with 3-4 setae, inner margin with 8-9 setae, carpalouter margin with 2 and inner with 3 setae respectively, propodal outer margin with 2 and innerwith 7-8 setae, dactylus with 2 inner proximal and 7 terminal setae; exopod 3-segmented, distalsegment with 5 terminal setae; epipod bifurcate, longer part setose. PEREIOPODS (Figs 8a-e). Cheliped (a) stout and with a prominent ischio-basal spine; inner distalpropodal margin and inner margin of dactylus with 3-4 blunt teeth. Pereiopods 2-5 (b-d) thin,inner margin of dactylus of each with 5-7 small spines, distal inner propodal margin with aspine, long on 2nd-3rd pereiopods; coxae of 2nd to 4th pereiopods each with a prominent spine,dactylus of 5th with 3 subterminal setae. ABDOMEN (Figs 8i, j). With 6 segments + telson; posterio-lateral margins rounded and with 1-2pairs of setae near dorso-lateral margin of each segment; telson slightly broader than long and LARVAL DEVELOPMENT OF GER YON TRIDENS 227 with 2 pairs of median setae. Five pairs of pleopods, exopod of each with 15 marginal plumosesetae on distal segment, basal segment of 5th (uropod) with a seta on outer margin; endopodsof pleopods 1-4 with 3 distally placed coupling hooks. First crab stage DIMENSIONS. C.L. 3-0-3-1 mm. CARAPACE (Fig. 8k). Slightly longer than broad, frontal region with a longitudinal medianfurrow; antero-lateral margins each with 2 well-developed teeth. PEREIOPODS (Fig. 8k). Cheliped moderately stout, carpal process acute. Pereiopods 2-5 longand thin, conspicuously setose. Taxonomic remarks The present laboratory reared material agrees with the account of the first zoea by Brattegard& Sankarankutty (1967) except in the following details. Brattegard & SankarankuttyTOTAL LENGTH : 2-0 mm ABDOMEN : ? Without setae near posterio- dorsal margin of segments 1-5 ANTENNULE: 4 aesthetascs+ 1 spinuleMANDIBLE: ? undifferentiated MAXILLULE: basal endite with 6 (5 in fig.) 'strong setae'; coxal endite with 7 setae MAXILLA: coxal endite with 10 setae; scaphognathite with 7 setae Present material2-6-2-8 mm with a pair of setae on posterio-dorsal margins of segments 1-5 2 aesthetascs + 2 short setae a clearly differentiated molarand incisor basal endite with 4 spines and 2setae; coxal endite with 9 setae coxal endite with 11 setae;scaphognathite with 8 setae The complete larval development of only one other species of Geryon (the western AtlanticG. quinquedens Smith) has been previously described (Perkins, 1973). The zoeal stages of thisspecies are noticably larger than those of G. tridens and dorso-lateral processes are usually deve-loped on the fifth abdominal segment in G. quinquedens, whilst the pair on the fourth are muchlarger than the small spines on the corresponding segment of G. tridens. The posterio-lateralprocesses on the fifth segment of the abdomen are also much larger than those of G. tridens. Themegalopa of G. quinquedens has only two subterminal setae on the dactylus of the fifth pereiopodcompared with three present in G. tridens, and the exopods of the first to fifth pleopods areinvested with 28 marginal setae whilst G. tridens has only 16. Further differences between thelarvae of the two species are apparent when the setation of the appendages is compared astabulated below. G. tridens G. quinquedens First zoea ANTENNULE:MAXILLULE: MAXILLA: 2 aesthetascs + 2 setaecoxal endite 9 setae basal endite 6 + 5 setaecoxal endite 4 + 3 setaescaphognathite 8 setae 4 aesthetascs + 1 setacoxal endite 6 setae basal endite 5 + 5 setaecoxal endite 3 + 3 setaescaphognathite 7 setae 228 R. w. INGLE G. tridens Second zoea ANTENNULE: 6 aesthetascsMAXILLULE: basal endite 6 spines + 5 setae MAXILLA: basal endite 7 + 7 setae scaphognathite 18 setae ISTMXPD: basis 8 setae 2ND MXPD: distal endopod segment 6 setae Third zoea ANTENNULE: 6 aesthetascs + 2 setaeMANDIBLE: palp not developed MAXILLULE: basal endite 6 spines + 12 setaecoxal endite 12-13 setae MAXILLA: basal endite 8 + 8 setae coxal endite 4 + 6 setaescaphognathite 25-29 setae Fourth zoea ANTENNULE: 1 1 aesthetascs + 3 setaeendopod bud not setose MAXILLULE: basal endite 6 spines + 18 setae MAXILLA: basal endite 1 1 + 10 setae coxal endite 5 + 8 setaescaphognathite 40-42 setae 2ND MXPD: exopod 17-18 setae Megalopa MAXILLULE: endopod 6 setae basal endite 14 spines + 12-13 setaecoxal endite 17 setae MAXILLA: endopod 2 basal setae; no lateral setaebasal endite 11+8 setaecoxal endite 6+13-14 setaescaphognathite 62-63 setae IST MXPD: exopod, proximal segment 5 disto-external setae, terminal segment 3 setae basal endite 33-34 setae 2ND MXPD: merus 5 marginal setaecarpus without setaedactylus 7 spines + 1 setaeproximal segment of exopodwithout setae 3RD MXPD: dactylus 9 setae exopod distal segment 5 setae G. quinquedens 4 aesthetascs12 spinous setae basal endite 7 + 5 setaescaphognathite 22 setae basis 10 setae distal endopod segment 4 setae 7 aesthetascs + 3 setaepalp developed basal endite 17 spinous setaecoxal endite 17 setae basal endite 7 + 5 setaecoxal endite 5 + 9 setaescaphognathite 31 setae 1 2 aesthetascs + 2 setaeendopod bud setose basal endite 22 spinous setae basal endite 12 + 9 setaecoxal endite 5 + 9 setaescaphognathite 54 setae exopod 19 setae endopod 4 setae basal endite 35 spinous setae coxal endite 25 setae endopod 3 basal setae; 8 lateral+ 1 proximal setaebasal endite 14+11 setaecoxal endite 8+16 setaescaphognathite 100 setae exopod, proximal segment6 disto-external setae, terminalsegment 5 plumose setaebasal endite 37 setae merus 3 marginal setaecarpus 3 setae dactylus 10 setae (or spines)proximal segment of exopodwith 4 marginal setae dactylus 12 setae exopod distal segment 6 setae LARVAL DEVELOPMENT OF GER YON TRIDENS 229 The zoeae of G. tridens can be readily distinguished from zoeae of all other brachyuran crabsreported from seas adjacent to the British Isles, except Goneplax rhomboides (Linnaeus), by thepresence of dorso-lateral spines on the fourth segment of the abdomen. The features that separateG. tridens zoeae from those of G. rhomboides are tabulated below. Zoeal features G. tridens G. rhomboides (after Lebour, 1928;Bourdillon-Casanova, 1960;Rice & Williamson, 1977) POSTERIO-LATERALMARGIN OF CARAPACE: MARGINS OF POSTERIO-LATERAL PROCESS OFABDOMINAL SEGMENTS TELSON FORKS: ANTENNAL EXOPOD: MAXILLA OF ZIII: 1ST MAXILLIPED endopod setae of ZIIIexopod setae of ZI-IV 2ND MAXILLIPED endopod setae of ZIIIexopod setae of ZI-IV with short spinules unarmed unarmed two lateral spines on each fork in ZI-III noticeably shorter thanspinous process in earlystages scaphognathite with25-29 setae 2,2,1,5+1 4, 9-10, 12-14, 17-18 1, 1,6 4, 9-10, 12-14, 16-17 with teeth and setae denticulate (see Bourdillon-Casanova, fig. 57a) with minute spinules one lateral spine on each fork in all stages almost, or as long as spinous pro-cess in early stages, shorter inlater stages scaphognathite with 18-19setae 3, 2, 1, 2, 5, 4, 6, 8, 9-10 1, 1,5 4, 6-7, 8-9,9-11 Megalopal features ROSTRUM: CARAPACE: G. tridens pointed unarmed G. rhomboides truncate with a pair of short protogastric spines The large number (16) of marginal uropod setae distinguish the megalopa of G. tridens fromthose belonging to the genera Polybius (10 setae), Macropipus (8-10 setae), Carcinus (5 setae),Xaiva (10 setae) and Portumnus (7 setae). In addition, the dactylus of the 5th pereiopod is styliformin G. tridens but conspicuously lanceolate in megalopae of Polybius, Macropipus and Portumnus. Juveniles of the deep water species Geryon affinis Milne Edwards & Bouvier have been oc-casionally misidentified as G. tridens. The dactyli of pereiopods 2-5 of G. tridens are stronglydorso-ventrally flattened whereas they are laterally compressed in G. affinis. This dorso-ventralflattening is apparent in G. tridens from the third crab stage (c.l. 5-0 mm) onwards, and may pro-vide a means for separating the early post-larval stages of both species when corresponding stagesof G. affinis become available for comparison. The N. Atlantic G. tridens is replaced southward by the closely related G. longipes A. MilneEdwards. The larval stages of this species are unknown although the first zoeal stage of 'Bathy-nectes sp. A' figured by Rice & Williamson (1977 : 47, fig. 22 a-d) is almost certainly a Geryonzoea and may be G. longipes. At present adults of both species can be separated only by differencesin relative lengths of pereiopods 2-5 and by the degree of development of the antero-lateral 230 R. W. INGLE carapace spines. In G. tridens the pereiopods are shorter and slightly stouter than those of G.longipes and the fifth is much less than twice the median length of the carapace. The antero-lateralcarapace spines are also shorter, less spinose, and usually directed slightly more anteriorly thanthose of G. longipes. A comparison of the smallest juvenile of G. longipes (c.l. 17 mm, from thesyntype series) with the largest reared crab of G. tridens (eighth stage c.l. 9-9 mm) has revealedthat the limb/carapace ratios are the same for both species. However, the juvenile of G. longipeshas the posterior pair of antero-lateral spines directed outward and set at an angle of a little lessthan 90 to the median axis of the carapace, whilst the corresponding pair of spines in G. tridensare directed forward as in the adult. Brachyuran zoeae hitherto described from British waters, with few exceptions (Ebalia, Lebour,1928 : 478; Corystes, Ingle & Rice, 1971 : 282), show regular increases of marginal setae on theexopods of the first and second maxillipeds (e.g. ZI 4 setae, ZII 6, ZIII 8, ZIV 10 and ZV 12setae, respectively). The zoeae of G. tridens do not conform to this pattern as laboratory rearedmaterial show the following succession of setal development and variation ZII 9-10 setae,ZIII 12-14, ZIV 16-18 setae. Irregular developmental sequences of exopod setae are, however,not unusual and occur in zoeae of the western Atlantic G. quinquedens and in some portunids(Callinectes sapidus, Costlow & Bookhout, 1959 and Ovalipes ocellatus, Costlow & Bookhout,1966). In these species the exopod setal formulae differ sufficiently on either one pair, or on bothpairs of maxillipeds, from one moult to the next to enable recognition of the individual zoealstages. Phylogenetic relationships The larvae of G. tridens possess many portunid features (family Portunidae). In particular, thezoeae have long, relatively non-spinulate rostral and dorsal spines, outwardly directed long lateralcarapace spines, a well-developed antennal exopod that is shorter than the spinous process,well-developed dorso-lateral processes on abdominal segments 2-3, a telson with three spinuleson each fork (with the smallest one becoming reduced in later stages), the first maxilliped withtwo setae on the endopod first segment and the distal setae on the endopod of the maxilla arrangedin three distinct groups. Larval characters separating the three subfamilies of the Portunidae represented in Britishwaters were given by Rice & Ingle (\915a : 148-149). Although the larvae of G. tridens do notpossess all the characters listed for any one of these three subfamilies they show, nevertheless,strong affinities to the Polybiinae. The zoeae have the third segment of the endopod of the firstmaxilliped armed with a seta and well-developed lateral spines on the carapace, whilst themegalopa is without sternal cornuae, but has coxal spines on pereiopods 2-4 with a downwardpointing rostrum, and the dorsal surface of the carapace is without spines or conspicuous pro-cesses. Zoeae belonging to the Portunidae have dorso-lateral processes on abdominal segments 2-3,although they may disappear from the third segment in later stages; only exceptionally are theseprocesses present on segments 4-5 (e.g. Ovalipes, Costlow & Bookhout, 1966, fig. la). Thesedorso-lateral processes are frequently well developed on the posterior abdominal segments ofzoeae belonging to the families Xanthidae (e.g. Menippe, Porter, 1960, fig. 2u; Panopeus, Lebour,1944, fig. 9 and Eriphia, Bourdillon-Casanova, 1960, fig. 55), the Goneplacidae (e.g. Goneplax,Lebour, 1928, PI. XI, fig. 10; XII, fig. 1) and Grapsidae (Plagusia, Aikawa, 1937, fig. 35). Thezoeae of Menippe and of Goneplax also have long posterio-lateral abdominal spines. The zoeae of G. tridens possess a small but conspicuous pair of dorso-lateral processes on thefourth abdominal segment and, in later stages, the posterio-lateral spines are well developed onthe second to fourth segment. In both features G. tridens shows affinities to the Xanthidae andGoneplacidae, whilst the first crab stage strongly resembles juveniles of the Goneplacidae (e.g.perhaps Homoioplax and Psopheticus) in having a sub-quadrate carapace with two antero-lateralteeth and long thin pereiopods, features that are not typical of the early post-larval stages ofeither xanthids or portunids. The genus Geryon was assigned to the family Goneplacidae by Rathbun (1937 : 265), Sakai LARVAL DEVELOPMENT OF GER YON TRIDENS 23 1 (1939 : 554-555) and by Barnard (1950 : 282), but Bouvier (1940 : 261) placed in into the familyXanthidae. Colosi (1924), however, had already established the family Geryonidae for GeryonKroyer, 1837 and the fossil genus Archaeogeryon. Balss (1957 : 1654) placed the Geryonidaebetween the Xanthidae and Goneplacidae. Boyden (1943) demonstrated serological affinitiesbetween Geryon quinquedens and a species of the family Xanthidae (Menippe) and Leone (1951)between species of Xanthidae and Portunidae (Macropipus puber), but these authors were notable to compare it with species in the Goneplacidae. Perkins (1973) also suggested that the larvaeof G. quinquedens shared many features with those larvae in the family Xanthidae. The presentstudy of the larval development of G. tridens supports this serological evidence and suggests thatthe Geryonidae may have been derived from the same phylogenetic stock as the Portunidae,Xanthidae and perhaps a part of the heterogenous Goneplacidae. Acknowledgements I wish to thank Mr K. Wilson and Mr M. Rolf of the MAFF Laboratory, Burnham-on-Crouch,for their generous assistance in obtaining the live Geryon female from which the larvae werereared, and Dr A. L. Rice, Institute of Oceanographic Sciences, for his comments on the manu-script. References Aikawa, H. 1937. Further notes on brachyuran larvae. Rec. oceanogr. Wks Japan 9 : 87-162. Balss, H. 1957. Decapoda . . . In: Dr H. G. Bronns Klassen und Ordnungen des Tierreichs. Funfter Band, I. Abteilung, 7. Buch., 12 Lief; 1505-1672, Leipzig.Barnard, K. H. 1950. Descriptive catalogue of South African Decapod Crustacea (Crabs and Shrimps). Ann. S. Afr. Mus. 38 : 1-837.Bourdillon-Casanova, L. 1960. Le meroplancton du Golfe de Marseille: ies larves de crustaces decapodes, Reel. Trav. Sta. mar. Endoume 30 : 1 -286. Bouvier, E. L. 1940. Decapodes Marcheurs. Faune Fr. 37 : 1-404.Boyden, A. A. 1943. Serology and animal systematics. Amer. Nat. 77 : 234-255.Brattegard, T. & Sankarankutty, C. 1967. On the prezoea and zoea of Geryon tridens Kroyer (Crustacea Decapoda). Sarsia 26 : 7-12.Christiansen, M. E. 1969. Marine invertebrates of Scandinavia, No. 2 Crustacea Decapoda Brachyura, 143 pp. Universitetsforlaget, Oslo.Colosi, G. 1924. Una specie fossile di Gerionide (Decapodi brachiuri). Boll. Soc. Nat. Napoli35(\l) 15 : 248-255.Costlow, J. D. Jr & Bookhout, C. G. 1959. The larval development of Callinectes sapidus Rathbun reared in the laboratory. BioL Bull. mar. biol. Lab. Woods Hole 116 : 373-396.1966. The larval development of Ovalipes ocellatus (Herbst) under laboratory conditions. J. Elisha Mitchell scient. Soc. 82 : 160-171. Ingle, R. W. & Clark, P. F. 1977. A laboratory module for rearing crab larvae. Crustaceana 32 : 220-222.& Rice, A. L. 1971. The larval development of the masked crab, Corystes cassivelaunus (Pennant), reared in the laboratory. Crustaceana 20 : 271-284. Kroyer, H. 1837. Geryon tridens, en ny Krabbe. Naturh Tidsskr. 1 : 15-21.Lebour, M. V. 1928. The larval stages of the Plymouth Brachyura. Proc. zool. Soc. Lond. 2 : 473-560. 1944. Larval crabs from Bermuda. Zoologica 29 : 113-128. Leone, C. A. 1951. A serological analysis of the systematic relationship of the Brachyuran crab Geryon quinquedens. Biol. Bull. mar. biol. Lab. Woods Hole 100 : 44-48.Perkins, H. C. 1973. The larval stages of the Deep Sea Red Crab Geryon quinquedens Smith, reared under laboratory conditions (Decapoda : Brachyrhyncha). Fishery Bull. natn. ocean, atmos. Adm. 71 : 69-82.Porter, H. J. 1960. Zoeal stages of the Stone Crab, Menippe mercenaria Say. Chesapeake Sci. 1 : 168-177.Rathbun, M. J. 1937. The oxystomatous and allied crabs of America. Bull. U.S. natn. Mus. 166 : i-vi, 1-278.Rice, A. L. & Ingle, R. W. 1975. The larval development of Carcinus maenas (L.) and C. mediterraneus Czerniavsky (Crustacea, Brachyura, Portunidae) reared in the laboratory. Bull. Br. Mus. nat. Hist. (Zool.) 28 : 101-119. 232 R. W. INGLE \915a. A comparative study of the larval morphology of the British Portunid crabs Macropipus puber (L.) and M. holsatus (Fabricius), with a discussion of generic and sub-familial larval characterswithin the Portunidae. Bull. Br. Mus. not. Hist. (Zool.) 28 : 121-151. & Williamson, D. I. 1977. Planktonic stages of Crustacea Malacostraca from Atlantic Seamounts. "Meteor" Forsch.-Ergebn., D, No. 26 : 28-64.Sakai, T. 1939. Studies on the crabs of Japan. IV. Brachygnatha, Brachyrhyncha, pp. 365-741. Yokendo Ltd, Japan.Steedman, H. F. (ed.) 1976. Zooplankton fixation and preservation. In: Monographs on oceanographic methodology, 350 pp. Paris.Zariquiey Alvarez, R. 1968. Crustaceos Decapodos Ibericos. Investigacion pesq. 32 : i-xi, 1-510. Manuscript accepted for publication 2 June 1978 Notes on the types of scorpions in the British Museum (Natural History), London Buthus socotrensis Pocock, 1889 (Family: Buthidae) Max Vachon Museum National d'Histoire Naturelle, Laboratoire des Arthropodes, 61 rue de Buffon, 75005Paris Resume L'etude des syntypes de Buthus socotrensis Pocock et de specimens conserves au British Museum (NaturalHistory) et au Museum national d'Histoire naturelle de Paris confirme la validite de cette espece jusqu'alorsnon retenue par les Specialistes. Buthus socotrensis doit etre place dans le genre Buthotus Vachon, 1949,mais les caracteres particuliers de sa trichobothriotaxie necessitent la creation d'un nouveau sous-genre:Balfourianus, creation confirmant Pendemisme de la faune scorpionique de 1'ile Socotra. Introduction Buthus socotrensis was first described by R. I. Pocock in 1889 on the examination of four specimenscollected from Socotra Island by Prof. B. Balfour. The description was then completed by Pocockin 1903. His new diagnosis corroborated K. Kraepelin's statement (1899) concerning the classifica-tion of the species in the hottentota-group of the genus Buthus. In 1914, A. Birula, studying specimens collected by Franz Werner from North Africa, re-examined the species belonging to Kraepelin's hottentota-group (which he considered of sub-generic value). As noted by Pocock Buthus socotrensis is not referable to the sub-genus but mustbe placed close to Buthus acutecarinatus Simon, 1883 and B. gibbosus Brulle, 1832. Pocock's species socotrensis was omitted from our revision of the family Buthidae and itsclassification was considered to be uncertain (Vachon & Stockmann, 1968). On the basis of the study of four specimens belonging to the type-series and kept in the BritishMuseum (Nat. Hist.) and of specimens from Socotra Island, deposited either in the Museumnational d'Histoire naturelle Paris (M.N.H.N.) or in the British Museum (B.M.), socotrensiscould be referred to the genus Buthotus Vachon, 1949; nevertheless, a new name becomes necessaryfor the new sub-genus. Balfourianus, named after the first collector of the species: Prof. BaillieBalfour, is thus proposed. Material examined Consists of 1 1 females, three of these belonging to the type-series, Prof. T. B. Balfour, B.M. reg.no. 18, 81-106: 1 female lectotype (B.M.), registered as VA 1621-1. Among the four specimens studied byR. I. Pocock, none has been designated as the type; therefore, the female, the measurements ofwhich correspond to the specimen originally described by R. I. Pocock (he. cit., 1889 : 339) hasbeen designated as the lectotype. 2 female paralectotypes (B.M.): VA 1621-2 and VA 1621-3. 3 females (B.M.): VA 1218, VA 1220, VA 1222, Oxford University Exp., Hadibu Plain,22.ix.1956, Socotra Island. 1 female (B.M.): VA 1695, Oxford University Exp., August 1956, Adho Dimellus, only underrock in damp areas, Socotra Island. Bull. Br. Mus. not. Hist. (Zool.) 36 (4) : 233-237 Issued 25 October 1979 233 234 BUTHOTUS ( Balf.)socotrensis ( Poc. ) it Figs 1 to 6 Right pedipalp of female paralectotype : VA 1621-2. 1, external side of chela; 2, ventralside of hand; 3, dorsal side of tibia ( = forearm); 4, external side of tibia; 5, dorsal side of femur( = arm); basal area of internal side of femur. Only the trichobothries have been figured. 1 female (B.M.): VA 1224, Socotra Island, lO.x.1956; Zool. Soc. Lond. leg. 2 females (M.N.H.N.P.): RS 4684, RS 4687, Socotra Island, Hadibu Plain, K. M. Guichardleg. 1967. 1 female (M.N.H.N.P.): RS 4686, Socotra Island, sea level, K. M. Guichard leg. 1967. and of 7 males : 1 male paralectotype (B.M.): VA 1621-4, Socotra Island, T. B. Balfour, 81-106. 1 male (B.M.): VA 1219, Zool. Soc. Lond. leg, 10.x. 1956, Socotra Island. 3 males (B.M.): VA 1221, VA 1225, VA 1226; Oxford Univ. Exp., 1956; Socotra Island. TYPE SCORPIONS IN THE BM(NH) 235 1 male (M.N.H.N.P.): RS 4685, Socotra Island, 28.iv.1967, Kalansya under palm fronds;K. M. Guichard leg. The study of these 17 specimens fully supports the existence of the characters given in Pocock'sdiagnosis. Some data concerning the trichobothriotaxy, the chaetotaxy, the caudal keels and thepectinal teeth number will supplement the original diagnosis. Trichobothriotaxy (Figs 1 to 6) It agrees with our description of the Buthotus-genus (loc. cit., 1949 : 145) but differs from it inthat the trichobothry db is always distal to et (Figs 1 to 8) instead of basal (Fig. 7). This ''invariant''disposition, i.e. unrelated to the sex or to the age of the specimen, is a taxonomic character ofprimary importance in easily discriminating between the Socotra Island species and the otherknown Buthotus species. On the basis of the relative positioning of the trichobothries et, est, dt,db, two sub-genera could be recognized in the genus Isometrus H. and E. (Vachon, 1972); in ourrevision of the genus Lychas C. L. Koch, this character has also been used. Chaetotaxy Among all the specimens examined, numerous and short setae, together with tergal ones, couldbe observed on the pedipalps (Polytrichy). The caudal segments only bear few setae, symmetricallyarranged (Oligotrichy). Caudal keels (metasoma) According to R. I. Pocock (1903), because of the presence of a paired keel on the upper surfaceof the segment, the fourth segment bears 12 keels (which is unusual). Its existence could be settled.The keel consists of a row of granulae which may also occur (but less regularly) on the dorsalgroove of almost all the segments, including the last one. It seems not to be a 'true 'keel. Number of pectinal teeth In R. I. Pocock's diagnosis (loc. cit., 1889 : 339) the sex of the specimens examined could not beascertained; neither was it stated whether the numbers indicated (24-25; 28-29) deal with in-dividual variations or with sexual ones. But, in 1903, the sexual origin of the variations could bestated, the pectines of the female bearing 24 or 25 teeth, whereas in males, they are 28 or 29. The sex of the 18 specimens at our disposal (1 1 females and 7 males) could easily be identified. The following combinations could be noted: in females: 23-25 (1 time); 25-24 (2 times); 25-25 (4 times); 26-25 (2 times); in males: 27-28 (1 time); 28-29 (1 time); 29-28 (1 time); 30-31 (1 time); 31-31 (1 time);31-32(1 time); 32-30(1 time). It may be pointed out that: 1. The number of pectinal teeth is a character of importance in discriminating between thesexes owing to the fact that in females it varies from 23 to 25, instead of from 27 to 32 in males. 2. The asymmetry is frequent, the number of teeth on the left side of a specimen differing fromthat found on the right one. Thus, of the 1 1 pairs of female pectines examined 7 are asymmetricaland in males, 6 of the 7 pairs of pectines are assymmetrical too. 3. The number 25 (referred to as type-number) is more frequently observed in females (15of the 22 pectines examined); in males, owing to the small number (7) of specimens available,it could not be ascertained, But it may be noted that the arithmetical mean of the teeth numberon each pectine is 29 (W)- Conclusions 1 . On the basis of its trichobothriotaxy, Buthotus socotrensis may be easily separated from theother known Buthotus sp. It permits recognition of two sub-genera in the genus Buthotus Vachon,1949: Balfourianus s.g. nov., to which the species socotrensis Pocock, 1889 may be referred andthe type-subgenus: Buthotus, which for the moment includes the other known species. 236 8 Figs 7 and 8 Right chela. 7, in Buthotus (Buthotus) sp. ; 8, in Buthotus (Balfourianus) socotrensis(Pocock). The 'territory' on which the position of db varies (according to species or to specimensbelonging to the same sub-genus) is hachured. Therefore, the generic diagnosis published in 1949 should be slightly modified according tothe remarks published in 1968 (Vachon & Stockmann, loc. cit. : 89). Revised diagnosis of the genus Buthotus Vachon, 1949 Concerning the positioning of the trichobothry db on the fixed finger, it may be noted that db ison the distal half of the finger but its position varies; it may be distal to et or between et and estor slightly basal to est. Diagnosis of the nominal subgenus: Buthotus (Buthotus) Characters very similar to those of the sub-genus but the trichobothry db is always basal to et. Diagnosis of the new subgenus Buthotus (Balfourianus) Characters very similar to those of the sub-genus but db is always distal to et.The two sub-genera may be separated by means of the following key: Fixed finger with db clearly distal to et (Figs 1 and 8) so that dt and db are both distal toet . ........ s.g. nov. Balfourianus Type: B. (B.) socotrensis (Pocock, 1889); Socotra Island. db between et and est or slightly basal to est (Fig. 7) . . . . . . s.g. Buthotus Type: B. (B.) judaicus (Simon, 1872); Africa and Asia. 2. Endemism could be ascertained from the existence of a sub-genus and of a species of Buthotusoccurring in Socotra Island as might be inferred from the presence of two other species which TYPE SCORPIONS IN THE BM(NH) 237 have never been collected elsewhere: Hemiscorpion socotranus Pocock, 1889 (Fam. Scorpionidae)and Butheolus insularis Pocock, 1889 (Fam. Buthidae).* It may be noted that an endemic genus, Heteronebo Pocock, 1889, could be observed in Abd-el-Kuri, a small island between Gardafui Cape and Socotra Island; two species: H. granti Pocock,1889 and H.forbesii Pocock, 1889 are assignable to the genus (Fam. Diplocentridae). The genushas never been collected from Somalia, from Socotra or from Arabia (O. F. Francke, 1977). References Birula, A. 1914. Ergebnisse einer von Prof. Franz Werner zoologischen Forschungsreise nach Algerien. VI: Skorpione und Solifugen. Sber. Akad. Wiss. Wien, 123 : 633-668.Francke, O. F. 1977. Taxonomic observations on Heteronebo Pocock (Scorpionida, Diplocentridae). /. Arachnol.,4 : 95-113. Kraepelin, K. 1889. Scorpiones und Pedipalpi, Tierreich. 8 : 1-265. Pocock, R. I. 1889. Notes on some Buthidae new and old. Ann. Mag. not. Hist., ser. 6, 3 : 334-351.1899. The expedition to Sokotra. III. Description of the new species of Scorpions, Centipedes and Millipedes. Bull. Lpool Mus. 2 : 7-9.1903. The scorpions and spiders of Sokotra. In: Henry O. Forbes, L.L.D.: The natural History of Sokotra and Abd-el-Kuri. Henry Young and Sons, Liverpool : 178-182. (Scorpions.)Vachon, M. 1949. Etudes sur les Scorpions. Arch. Inst. Pasteur Algerie 17 (2) : 132-169.1972. Remarques sur les Scorpions appartenant au genre Isometrus H. et E. (Buthidae) a propos de Pespece Isometrus maculatus (Geer) habitant Pile de Paques. Cah. pacif. 16 : 169-180.& Stockmann, R. 1968. Contribution a Petude des Scorpions africains appartenant au genre Buthotus Vachon, 1949 et etude de la variabilite. Monitore zool. ital., n.s., 2 (suppl.) : 81-149. *O. F. Francke (1977) points out the presence of three endemic species on Socotra Island: Hemiscorpion soco-tranus Pocock (Scorpionidae), Butheolus insularis Pocock (Buthidae) and Orthochirus socotrensis Pocock (Buthidae).Buthotus socotrensis (Pocock) is not mentioned. On our part, we have no data concerning Orthochirus socotrensis(Pocock). Manuscript accepted for publication 3 May 1978. Five new prawn-associated gobies (Teleostei :Gobiidae) of the genus Amblyeleotris Nicholas V. C. Polunin & Roger Lubbock Zoological Laboratory, Downing Street, Cambridge CB2 3EJ Synopsis Five new species of prawn-associated gobies belonging to the genus Amblyeleotris Bleeker are described:A. rhyax from the Philippines and Bismarck Archipelago, A. callopareia and A. macronema from theGreat Barrier Reef, A. latifasciata from the Gulf of Thailand and Philippines, and A. diagonalis fromvarious localities in the Indian Ocean and Western Pacific. Introduction The genus Amblyeleotris Bleeker is close to Cryptocentrus Ehrenberg and includes approximatelytwenty species of gobies found in association with alpheid prawns in the Indo-Pacific region(Hoese & Steene, ms.; Polunin & Lubbock, in press). The purpose of the present study is to provide descriptions of five previously unrecorded species :Amblyeleotris rhyax from the Philippines and Bismarck Archipelago, A. callopareia and A.macronema from the Great Barrier Reef, A. latifasciata from the Gulf of Thailand and Philippines,and A. diagonalis from various localities in the Indian Ocean and Western Pacific. Methods of description follow Polunin & Lubbock (1977). Type specimens are deposited atthe British Museum (Natural History), London (BMNH), the Australian Museum, Sydney(AMS), the National Museum of Natural History, Washington (USNM), the Museumd'Histoire Naturelle, Geneve (MHNG), and the Bernice P. Bishop Museum, Honolulu (BPBM). Amblyeleotris rhyax n. sp. (Fig. 1)MATERIAL EXAMINED (a) Holotype, 63-7 mm S.L. (standard length), in sandy gully amongst coral at 35 m depth,Nodup, near Rabaul, New Britain, Bismarck Archipelago, coll. R. Lubbock on 1.8.1975;BMNH 1978.2.28.8. (b) Paratype, 72-5 mm S.L. (ripe ?), rubble near cave at 35-45 m depth, Nodup, near Rabaul,New Britain, Bismarck Archipelago, coll. R. Lubbock & B. Parkinson on 29.7.1975; USNM.218978. (c) Paratype, 70-0 mm S.L., 30 rubble slope at 35m depth, Maribago, MactanIsland, Cebu Strait, Philippine Islands, coll. R. Lubbock on 6.8.1976; AMS. 1.20688-001. DESCRIPTION. Dorsal fin rays VI + 1 12 (last ray divided to base); anal fin rays I 12 (last raydivided to base); pectoral fin rays 19-20; pelvic fin rays I 5. 66-71 rows of scales in lateral seriesfrom dorsal angle of branchial opening to base of caudal fin, latter with an additional 3-4 rowsbasally; 24-27 transverse scale series, counted forwards and upwards from first anal spine toapproximately below sixth dorsal spine; 21-24 scales in a zigzag series around narrowest part ofcaudal peduncle. Gill rakers on lower limb of first arch, including elongate raker at angle, 10 or1 1 (all elements counted). The following measurements are presented as percentages of the S.L. Head length 29-6-32-1,mean 31-2; snout length 6-2-7-7, mean 6-8; orbit diameter 6-3-6-5, mean 6-4; predorsal length31-7-33-8, mean 32-6; snout to origin of second dorsal fin 53-6-55-4, mean 54-6; snout to originof anal fin 57-5-63-5, mean 60-5; body depth at pelvic fin origin 18-0-20-1, mean 19-0; body widthjust behind operculum 13-5-15-8, mean 14-4; least depth of caudal peduncle 10-0-10-4, mean Bull. Br. Mus. nut. Hist. (Zool.) 36 (4) : 239-249 Issued 25 October 1979 239 240 N. V. C. POLUNIN & R. LUBBOCK 10-1; dorsal fin base length 50-1-51-3, mean 50-8; first dorsal spine length 12-7-23-1, mean 18-2;second dorsal spine length 14-1-27-1, mean 20-2; third dorsal spine length 15-6-28-0, mean 22-9;fourth dorsal spine length 15-5-29-0, mean 20-5; anal fin base length 23-7-26-2, mean 25-1;pectoral fin length 23-0-24-7, mean 23-7; pelvic fin length 29-3-32-2, mean 30-9; caudal fin length31-5-34-2, mean 33-1. Small elongate fish, head and body moderately compressed. Mouth rather large, gape oblique,jaws nearly equal anteriorly (lower jaw protruding slightly in 70-0 mm S.L. paratype), reachingposteriorly approximately to a vertical through centre or hind margin of pupil; upper lip asbroad (vertically at front) as lower. Gill opening extending forwards ventrally to verticallybelow a point just posterior to hind margin of orbit. Fig. 1 Diagram showing the live colour pattern of Amblyeleotris rhyax, based on the paratype(70-0 mm S.L.) from the Philippine Islands. Upper jaw with one or two series of fine, sharp, subconical teeth, about three series at sym-physis; outer series larger and more caniniform posteriorly, increasingly so anteriorly, with twoparticularly enlarged teeth anteriorly on each side of jaw. Lower jaw posteriorly with one seriesof fine, sharp, subconical teeth, about three series at symphysis; outer series larger and morecaniniform posteriorly, increasingly so anteriorly with one or two (two on one side in holotype,one in all other cases) greatly enlarged teeth anterolaterally on each side of jaw. Gill membranes rather narrowly attached at isthmus. Anterior and posterior nostrils separatedby a space about equal to width of posterior nostril; posterior nostril oval, about equal in sizeto round anterior nostril, separated from eye by space about equal to its width; anterior nostrilwith short membranous tube. Opercular edge entire, preopercular edge smooth. Scales cycloid anteriorly, becoming ctenoidlaterally approximately below hind margin of first dorsal fin. Head almost naked, with a fewscales on nape above dorsal angle of branchial opening; midline of nape scaled. Dorsal and analfins naked; pelvic fins with embedded scales on base; pectoral fins scaled on base; caudal fin withapproximately basal seventh scaled. Sensory papillae on head moderately developed. Dorsal fin divided into two parts, not connected by membrane; first part with six spines, second,third and fourth spines longest; second part with a single spine followed by branched rays. Analfin with a single spine followed by branched rays. Origin of anal fin approximately at a verticalbelow first or second dorsal soft rays. Posterior margins of second dorsal and anal fins pointed.Caudal fin somewhat pointed. Pectoral fins rounded, reaching approximately to anus or to originof anal fin. Origin of pelvic fins below pectoral fin base; fourth pelvic soft ray longest, reaching toanus or beyond anal fin origin, about three times as long as pelvic spine; fins united by very lowmembrane, without fraenum. Colouration. In life, head and body whitish, with four bright red vertical to oblique bands andscattered golden spots; first band from below eye, behind posterior tip of jaw to underside ofhead; second band across part of predorsal area and hind margin of operculum to underside ofhead ; third band from below fifth to sixth dorsal spines to just behind pelvic fin base; fourth band NEW SPECIES OF THE GENUS AMBLYELEOTRIS 241 fainter, from below third to fourth dorsal soft rays to bases of first and second anal rays. Firstand second vertical bands join a bright red band covering ventral profile of head and body an-terior to pelvic fin base. First dorsal fin pale blue with scattered golden spots; second dorsal finpale blue with golden spots, mostly in two horizontal series. Anal fin pale blue with two horizontalrows of blue spots near base, distally with approximately horizontal golden and dark blue brokenlines. Pelvic fins pale blue with a streak of red along inner margin. Pectoral fins hyaline. Caudalfin mainly pale blue, with yellowish tinge along central rays and three to four orange spots at base.In alcohol, head and body brownish, with bands and spots remaining visible as paler markings.Dorsal, caudal and anal fins pale brown, golden spots becoming hyaline. Pectoral fins hyaline.Pelvic fins brownish. Fig. 2 Diagram showing the live colour pattern of Amblyeleotris callopareia, based on the holotype(78-0 mm S.L.) from the Great Barrier Reef. REMARKS. Amblyeleotris rhyax most closely resembles A. guttata (Fowler, 1938), but the twospecies can be easily distinguished by live colouration. In A. rhyax there are four bright red verticalbands on the head and body (absent in A. guttata), and the golden spots on the body do not con-tinue onto the base of the anal fin (as they do in A. guttata); furthermore, the area of charcoalgrey colouration which covers the ventral part of the body anterior to the anus in A. guttata isabsent from A. rhyax. The name rhyax is derived from pua, Greek for volcano, and refers to the fiery colours of thepresent species. HABITAT AND DISTRIBUTION. Amblyeleotris rhyax is known from New Britain and the PhilippineIslands. It has only been found on outer reef slopes, where it inhabits burrows made by alpheidprawns in sand and rubble at depths usually in excess of 30-40 m. Amblyeleotris callopareia n. sp. (Fig. 2)MATERIAL EXAMINED (a) Holotype, 78-0 mm S.L., at 26 m depth, coarse sand 50-100 m seaward of coral at bottomof reef slope, just east of South Island, Lizard Island, Great Barrier Reef, coll. R. Lubbock on24.5.1975; BMNH 1978.2.28.1. (b) Paratype, 68-2 mm S.L., coll. with (a); AMS. 1.20689-001. (c) Paratype, 34-7 mm S.L., coll. with (a); USNM. 218980. DESCRIPTION. Dorsal fin rays VI + 1 12 (last ray divided to base); anal fin rays I 12-13 (last raydivided to base); pectoral fin rays 19-20; pelvic fin rays I 5. 69-75 rows of scales in lateral seriesfrom dorsal angle of branchial opening to base of caudal fin, latter with an additional 3-4 rowsbasally; 21-25 transverse scale series, counted forwards and upwards from first anal spine toapproximately below sixth dorsal spine; 19-23 scales in a zigzag series around narrowest part ofcaudal peduncle. Gill rakers on lower limb of first arch, including elongate raker at angle, 9 or10 (all elements counted). 242 N. V. C. POLUNIN & R. LUBBOCK The following measurements are presented as percentages of the S.L. Head length 25-8-31-1,mean 28-0; snout length 5-4-6-9, mean 5-9; orbit diameter 5-6-6-9, mean 6-2; predorsal length31-5-36-3, mean 33-5; snout to origin of second dorsal fin 53-3-57-6, mean 55-3; snout to originof anal fin 55-2-61-9, mean 59-5; body depth at pelvic fin origin 15-8-18-4, mean 16-8; bodywidth just behind operculum 11-1-13-2, mean 12-3; least depth of caudal peduncle 10-1-10-8,mean 10-4; dorsal fin base length 49-8-54-2, mean 52-5; first dorsal spine length 17-2-18-7,mean 17-8; second dorsal spine length 14-4-20-7, mean 18-3; third dorsal spine length 18-7-21-2,mean 20-2; fourth dorsal spine length 19-3-20-9, mean 20-1; anal fin base length 23-9-30-8,mean 27-6; pectoral fin length 22-4-27-0, mean 24-0; pelvic fin length 26-0-26-8, mean 26-3; caudalfin length 34-7-37-8, mean 35-9. Small elongate fish, head and body moderately compressed. Mouth rather large, gape oblique,jaws nearly equal anteriorly; upper lip as broad (vertically at front) as lower. Gill openingextending forwards ventrally to vertically below a point approximately one-third of way fromhind margin of orbit to posterior margin of operculum. Upper jaw posteriorly with one or two series of fine, sharp, subconical teeth, about five seriesat symphysis; outer series larger and more caniniform posteriorly, increasingly so anteriorly,with two particularly enlarged teeth anteriorly on each side of jaw. Lower jaw posteriorly withone or two series of fine, sharp, subconical teeth, about five series at symphysis; outer series largerand more caniniform posteriorly, increasingly so anteriorly, with three particularly enlargedteeth anterolaterally on each side of jaw. Gill membranes rather narrowly attached at isthmus. Anterior and posterior nostrils separatedby a space about twice length of posterior nostril; posterior nostril oval, about 2| times size ofround anterior nostril, separated from eye by space equal to two-thirds of its length; anteriornostril with short membranous tube. Opercular edge entire, preopercular edge smooth. Scales cycloid anteriorly, becoming ctenoidlaterally approximately below sixth dorsal spine. Head largely naked; midline of nape scaled.Dorsal and anal fins naked; pelvic and pectoral fins with scales on base; caudal fin with approxi-mately basal sixth scaled. Sensory papillae on head moderately developed. Dorsal fin divided into two parts, not connected by membrane; first part with six spines, second,third and fourth spines longest; second part with a single spine followed by branched rays. Originof anal fin approximately at a vertical through first or second dorsal soft rays. Posterior marginsof second dorsal and anal fins pointed. Caudal fin somewhat pointed. Pectoral fins rounded,reaching approximately to anus. Origin of pelvic fins below pectoral fin base; fourth pelvic softray longest, reaching to anus or anal fin origin, about three times as long as pelvic spine; finsunited, with fraenum. Colouration. In life, head and body pale beige with 5 faint vertical to oblique brown bands,and yellow stripes and spots; first band particularly faint, across part of predorsal area abovedorsal angle of branchial opening; second band below fifth to sixth dorsal spines; third bandbelow second to fifth dorsal soft rays; fourth band starting from below, and just posterior to,twelfth dorsal soft ray; fifth band on caudal fin base. Irregular scattered spots and patches ofbrown in between vertical bands. Three more or less vertical golden yellow stripes on head; firststripe from behind centre of hind margin of orbit to half-way down to posterior tip of jaw;second stripe on hind part of preoperculum; third stripe on operculum; a few scattered goldenyellow spots above stripes on head; scattered very faint pale yellow spots on body. First dorsalfin very pale beige with very faint horizontal to oblique lines of pale blue and faint orange distalmargin, latter most notable between tips of fourth and fifth spines; second dorsal fin similar tofirst dorsal fin, but with faint dark margin. Anal fin pale greenish beige with black distal marginlined on each side by pale iridescent blue. Pelvic fins pale blue. Pectoral fins hyaline. Caudal finvery pale beige with faint pale blue speckles; ventral margin coloured similarly to distal margin ofanal fin; dorsal margin dark, similar to distal margin of second dorsal fin; series of small bluespots posteriorly in upper half of fin, separated from margin by pale bluish band. In alcohol, head and body pale beige to brown, with brown bands and markings visible as NEW SPECIES OF THE GENUS AMBLYELEOTRIS 243 patches of darker brown. Dorsal fins pale beige to hyaline, first dorsal fin with orange marginstill visible as black area; bands still visible on anal fin in differing shades of brown; pelvic finsbrown ; pectoral fins hyaline ; caudal fin brown with traces of markings still clearly visible. REMARKS. Amblyeleotris callopareia most closely resembles A. macronema', the two species caneasily be distinguished by lateral (97-103 in A. macronema; 69-94 in A. callopareia) and trans-verse (29-32 in A. macronema', 21-25 in A. callopareia) scale counts, and by colouration (goldenmarkings on side of head present in A. callopareia, absent in A. macronema). The Greek KaXXorcapeios means beautiful-cheeked, and refers to the distinctive colouration onthe side of the head. HABITAT AND DISTRIBUTION. Amblyeleotris callopareia is known only from the Great BarrierReef, Austrialia, where it was collected on sand at the base of the reef slope at a depth of 26 moff Lizard Island. It was in association with burrowing alpheid prawns. Fig. 3 Diagram showing the live colour pattern of Amblyeleotris macronema, based on the holotype(80-0 mm S.L.) from the Great Barrier Reef. Amblyeleotris macronema n. sp. (Fig. 3)MATERIAL EXAMINED (a) Holotype, 80-0 mm S.L., at 26 m depth, coarse sand 50-100 m seaward of coral at bottomof reef slope, just east of South Island, Lizard Island, Great Barrier Reef, coll. R. Lubbock on24.5.1975; BMNH 1978.2.28.5. (b) Paratype, 77-8 mm S.L., coll. with (a); AMS. 1.20689-002. (c) Paratype, 51-6 mm S.L., coll. with (a); USNM. 218979. (d) Paratype, 50-0 mm S.L., coll. with (a); MHNG 1592.51. DESCRIPTION. Dorsal fin rays VI + 1 12-13 (last ray divided to base); anal fin rays 1 13 (last raydivided to base); pectoral fin rays 16-20; pelvic fin rays I 5. 97-103 rows of scales in lateral seriesfrom dorsal angle of branchial opening to base of caudal fin, latter with an additional 4-6 rowsbasally; 29-32 transverse scale series, counted forwards and upwards from first anal spine toapproximately below sixth dorsal spine; 26-27 scales in a zigzag series around narrowest part ofcaudal peduncle. Gill rakers on lower limb of first arch, including elongate raker at angle, 9 or10 (all elements counted). The following measurements are presented as percentages of the S.L. Head length 25-8-29-6,mean 27-8; snout length 5-0-7-4, mean 6-2; orbit diameter 5-8-6-4, mean 6-1; predorsal length28-7-33-9, mean 31-4; snout to origin of second dorsal fin 51-1-55-6, mean 53-8; snout to originof anal fin 55-0-57-9, mean 56-8; body depth at origin of pelvic fin 15-0-17-6, mean 16-6; bodywidth just posterior to operculum 10-2-11-2, mean 10-6; least depth of caudal peduncle 9-0-9-8,mean 9-2; dorsal fin base length 52-3-56-0, mean 53-9; first dorsal spine length 14-7-16-4, mean15-5; second dorsal spine length 18-6-27-2, mean 20-9; third dorsal spine length 30-4-42-8, mean 244 N. V. C. POLUNIN & R. LUBBOCK 33-7; fourth dorsal spine length 31-2-39-2, mean 35-0; anal fin base length 27-8-30-2, mean 29-0;pectoral fin length 20-4-22-2, mean 21-4; pelvic fin length 26-0-30-6, mean 27-7; caudal fin length35-3-41-0, mean 37-4. Small elongate fish, head and body moderately compressed. Mouth rather large, gape oblique,jaws nearly equal anteriorly (lower jaw protruding slightly in holotype), reaching posteriorlyapproximately to a vertical through centre of pupil (behind centre of pupil in larger specimens;anterior to centre of pupil in smaller specimens); upper lip as broad (vertically at front) as lower.Gill opening extending forwards ventrally to vertically below a point just posterior to hindmargin of orbit. Upper jaw posteriorly with one or two series of fine, sharp, subconical teeth, about five seriesat symphysis; outer series slightly larger and more caniniform posteriorly, increasingly so an-teriorly, with 2-3 greatly enlarged teeth anteriorly in each side of jaw. Lower jaw posteriorlywith one series of fine, sharp, subconical teeth, about four series at symphysis; outer series slightlylarger and more caniniform posteriorly, increasingly so anteriorly, with a single particularlyenlarged recurved canine anterolaterally on each side of jaw. Gill membranes rather narrowly attached at isthmus. Anterior and posterior nostrils separatedby space about three times width of posterior nostril; posterior nostril round, larger than roundanterior nostril, separated from eye by space about equal to twice its width; anterior nostrilwith short membranous tube. Opercular edge entire, preopercular edge smooth. Scales cycloid anteriorly, becoming ctenoidlaterally between sixth dorsal spine and hind margin of first dorsal fin. Head almost naked, witha few scales on nape above dorsal angle of branchial opening; midline of nape not scaled. Dorsaland anal fins naked; pelvic fins mostly naked, with a few embedded scales on base; pectoral finsmostly naked, with a few embedded scales near ventral margin of base; caudal fin with approxi-mately basal sixth scaled. Sensory papillae on head moderately developed. Dorsal fin divided into two parts, not connected by membrane; first part with six spines, thirdand fourth spines longest; second part with a single spine followed by branched rays. Anal finwith a single spine followed by branched rays. Origin of anal fin approximately at a verticalthrough second soft dorsal ray. Posterior margins of second dorsal and anal fins somewhatangular. Caudal fin lanceolate. Pectoral fins rounded, reaching about nine-tenths of way to analfin origin. Origin of pelvic fins below pectoral fin base; fourth pelvic soft ray longest, reaching tojust beyond anus or to origin of anal fin, about three times as long as pelvic spine; fins united,with low fraenum over approximately basal fifth of fins. Colouration. In life, head and body pale beige, with 5 faint brown vertical bands; first bandacross part of predorsal area, continuing onto dorsal part of operculum; second band belowfifth and sixth dorsal spines, fading ventrally; third band below second to fifth dorsal soft rays;fourth band below tenth to twelfth soft dorsal rays; fifth band on caudal fin base. Scattered patchesof pale brown between vertical bands. Brown band along midline of ventral profile of head,lined with pale blue; a few pale blue spots on and above preoperculum. First dorsal fin very palebeige with pale blue and orange spots, latter arranged regularly along spines and becomingbrighter distally; second dorsal fin very pale beige with a few orange spots along anterior anddistal margins. Anal fin pale bluish hyaline distally, pale beige along base, the two colours separatedby iridescent pale blue band and broad horizontal black stripe. Pelvic fins pale bluish hyaline.Pectoral fins hyaline. Caudal fin very pale beige, ventral half with dark streaks lined with paleblue, dorsal half with faint orange margin and scattered pale blue spots near upper edge. In alcohol, head and body pale beige with brown bands and patches still visible. Spots ondorsal fins scarcely visible; black stripe on anal fin remains striking; pelvic and pectoral finshyaline; black streaks on lower half of caudal fin remain visible REMARKS. Amblyeleotris macronema is close to A. callopareia; for a comparison between thetwo species see 'Remarks' under A. callopareia. The name macronema comes from the Greek uaicpos ( = long) and un.ua ( = thread), and refersto the long spines of the first dorsal fin. NEW SPECIES OF THE GENUS AMBLYELEOTRIS 245 HABITAT AND DISTRIBUTION. Amblyeleotris macronema is known from Lizard Island, GreatBarrier Reef, where it was found on coarse sand at the base of the reef slope at a depth of 26 m;it lives in association with burrowing alpheid prawns. Amblyeleotris diagonalis n. sp. (Fig. 4) MATERIAL EXAMINED (a) Holotype, 37-5 mm S.L., at 25 m depth on coarse sand 10-30 m seaward of coral at bottomof reef slope, just east of South Island, Lizard Island, Great Barrier Reef, coll. R. Lubbock on23.5.1975; BMNH 1978.2.28.2. Fig. 4 Diagram showing the live colour pattern of Amblyeleotris diagonalis, based on the paratype(59-5 mm S.L.) from the Andaman Sea. (b) 2 Paratypes, 44-1-51-9 mm S.L., coll. with (a); AMS. 1.20690-001. (c) 2 Paratypes, 45-9-56-0 mm S.L., on sand on reef flat at 6 m depth, southeast side of NossiIranja, northwest Madagascar, coll. N. Polunin on 9.7.1973; MHNG 1592.49-50. (d) Paratype, 39-1 mm S.L., sand adjacent to coral reef at 17 m depth, south side of Tany KelyIsland, Nossi Be, Madagascar, coll. N. Polunin on 30.6.1973; BMNH 1978.2.28.3. (e) Paratype, 32-0 mm S.L., on sand next to rock at 20 m depth, Lively Rocks, Trincomalee,Sri Lanka, coll. J. E. Randall on 3.4.1975; BPBM 18821. (f) 2 Paratypes, 36-2-39-7 mm S.L., on rubble and sand at 10m depth, north side of FortFrederick Peninsula, Trincomalee, Sri Lanka, coll. J. E. Randall on 3-5.4.1975; BPBM 18821. (g) Paratype, 59-5 mm S.L., on rubble and sand interspersed with coral at 30 m depth, westpoint of Born (Perforated) Island, eastern Andaman Sea, coll. N. Polunin & R. Lubbock on8.3.1977; USNM. 218981. DESCRIPTION. Dorsal fin rays VI + 1 13 (last ray divided to base) ; anal fin rays I 1 3 (last ray dividedto base); pectoral fin rays 19-20; pelvic fin rays I 5. 67-75 rows of scales in lateral series fromdorsal angle of branchial opening to base of caudal fin, latter with an additional 4-5 rows basally;23-24 transverse scale series, counted forwards and upwards from first anal spine to approximatelybelow sixth dorsal spine; 19-22 scales in a zigzag series around narrowest part of caudal peduncle.Gill rakers on lower limb of first arch, including elongate raker at angle, 8-10 (all elementscounted). The following measurements are presented as percentages of the S.L. Head length 26-7-29.9,mean 27-9; snout length 5-7-6-9, mean 6-4; orbit diameter 6-7-8-2, mean 7-5; predorsal length32-2-34-4, mean 33-1 ; snout to origin of second dorsal fin 52-1-54-6, mean 53-5; snout to originof anal fin 55-9-57-4, mean 56-8; body depth at pelvic fin origin 15-8-19-6, mean 17-3; body widthjust behind operculum 11-0-12-8, mean 11-7; least depth of caudal peduncle 9-3-10-9, mean 10-2;dorsal fin base length 49-1-55-6, mean 52-4; first dorsal spine length 16-6-29-2, mean 22-6; 246 N. V. C. POLUNIN & R. LUBBOCK second dorsal spine length 17-4-27-7, mean 23-5; third dorsal spine length 16-5-28-0, mean 21-9;fourth dorsal spine length 13-0-20-6, mean 17-0; anal fin base length 27-2-30-0, mean 28-5;pectoral fin length 21-5-26-1, mean 23-9; pelvic fin length 29-4-33-1, mean 30-8; caudal fin length29-6-42-1, mean 34-6. Small elongate fish, head and body moderately compressed. Mouth rather large, gape oblique,jaws nearly equal anteriorly, reaching posteriorly approximately to a vertical through centreof pupil; upper lip as broad (vertically at front) as lower. Gill opening extending forwards ventrallyto vertically below a point one-quarter of way from hind margin of orbit to posterior edge ofpreoperculum. Upper jaw posteriorly with two series of fine, sharp, subconical teeth, about four series atsymphysis; outer series larger and more caniniform posteriorly, increasingly so anteriorly, withthree to four particularly enlarged teeth anteriorly in each side of jaw. Lower jaw posteriorly withone series of fine, sharp, subconical teeth, about five series at symphysis; outer series generallylarger and more caniniform, especially anteriorly, with four particularly enlarged teeth anteriorlyin outer series, and three to four particularly enlarged teeth anterolaterally in inner series, ineach side of jaw. Gill membrane rather narrowly attached at isthmus. Anterior and posterior nostrils separatedby a space about equal to width of posterior nostril; posterior nostril oval, about equal in size toround anterior nostril, separated from eye by space slightly less than its width ; anterior nostrilwith short membranous tube. Opercular edge entire, preopercular edge smooth. Scales cycloid anteriorly, becoming ctenoidlaterally approximately below origin of dorsal fin. Head almost naked, with a few scales on napeabove dorsal angle of branchial opening; midline of nape scaled. Dorsal and anal fins naked;pelvic fins with embedded scales on base ; pectoral fins scaled on base ; caudal fin with approxi-mately basal fifth scaled. Sensory papillae on head moderately developed. Dorsal fin divided into two parts, not connected by membrane; first part with six spines, first,second and third spines longest; second part with a single spine followed by branched rays.Anal fin with single spine followed by branched rays. Origin of anal fin approximately at a verticalbelow first to second dorsal soft rays. Posterior margins of second dorsal and anal fins pointed.Caudal fin somewhat pointed. Pectoral fins rounded, reaching approximately to just beyond anus.Origin of pelvic fins below pectoral fin base; fourth pelvic soft ray longest, usually marginallylonger than fifth, reaching to bases of first to third anal soft rays, about three times as long aspelvic spine; fins united by a very low membrane, without fraenum. Colouration. In life, head and body whitish, becoming greyish dorsally, with six oblique brownbands; first band narrower and darker than others, from nape to posterior tip of maxilla; secondband from predorsal area across operculum; third band from bases of fifth and sixth dorsalspines; fourth band from bases of third and fourth dorsal soft rays; fifth band from bases oftenth to twelfth dorsal soft rays; sixth band on caudal peduncle, anterior to caudal fin base.Pale iridescent blue narrow lines on preoperculum, operculum and nape, mostly adjacent andparallel to first and second oblique brown bands. Traces of brown, mostly spots, dorsally betweenoblique body bands; thin brown lines from each eye anteriorly to tip of snout. First dorsalfin whitish hyaline, with small red spots margined with pale blue; second dorsal fin yellowishbasally with faint blue markings, distal half pale brownish hyaline. Anal fin with light yellowishbasal band, separated from greyish hyaline distal half by one blue and one red (distally) line.Pelvic fins whitish with faint blue and red tinges. Pectoral fins hyaline. Caudal fin yellowish withfaint pale blue spots, and brown crescent formed by faint brown bar just posterior to base of finextending ventrally and dorsally towards hind margin of fin. In alcohol, head and body pale beige, with bands, lines on snout, and spots pale to darkbrown. Dorsal, caudal, pectoral and pelvic fins largely hyaline. Anal fin mostly hyaline, with blueand red horizontal lines turning dark brown. REMARKS. Amblyeleotris diagonalis is close to A. steinitzi (Klausewitz, 1974) and A. japonicaTakagi, 1957, but may easily be distinguished by colouration. In A. diagonalis there is a con- NEW SPECIES OF THE GENUS AMBLYELEOTRIS 247 spicuous, narrow, dark brown band from the nape to the posterior tip of the maxilla; this isabsent in both A. steinitzi and A. japonica.The Latin name diagonalis refers to the oblique bands on the body. HABITAT AND DISTRIBUTION. Amblyeleotris diagonalis has a wide distribution, having beencollected in Madagascar, Sri Lanka and the Andaman Sea, and also on the Great Barrier Reef.It occurs in sandy habitats, where it lives symbiotically with burrowing alpheid prawns. Fig. 5 Diagram showing the live colour pattern of Amblyeleotris latifasciata, based on the holotype(65-1 mm S.L.) from the Philippine Islands. Amblyeleotris latifasciata n. sp. (Fig. 5)MATERIAL EXAMINED (a) Holotype, 65-1 mm S.L., at 15 m depth, on rubble at a distance of 10 m from nearest coral,passage between Cabulan Island and Vandanon Island, Cebu Strait, Philippine Islands, coll.R. Lubbock on 21.8.1976; BMNH 1978.2.28.4. (b) Paratype, 75-3 mm S.L., on sand and rubble at 10-25 m depth, north side of Chuang Island,offSamae San, Sattahip, Gulf of Thailand, coll. N. Polunin & R. Lubbock on 15.3.1977; AMS.1.20691-001. (c) Paratype, 67-2 mm S.L., coll. with (b); USNM. 218982. DESCRIPTION. Dorsal fin rays VI + 1 13 (last ray divided to base); anal fin rays I 13 (last raydivided to base); pectoral fin rays 20; pelvic fin rays I 5. 87-92 rows of scales in lateral seriesfrom dorsal angle of branchial opening to base of caudal fin, latter with an additional 3-5 rowsbasally; 29-30 transverse scale series, counted forwards and upwards from first anal spine toapproximately below sixth dorsal spine; 25 scales in a zigzag series around narrowest part ofcaudal peduncle. Gill rakers on lower limb of first arch, including elongate raker at angle, 9 or10 (all elements counted). The following measurements are presented as percentages of the S.L. Head length 26-7-27-4,mean 27-1; snout length 5-2-5-3, mean 5-2; orbit diameter 6-1-6-2, mean 6-1; predorsal length30-7-33-4, mean 32-2; snout to origin of second dorsal fin 50-3-53-2, mean 51-8; snout to originof anal fin 52-8-55-2, mean 54-2; body depth at pelvic fin origin 15-0-16-0, mean 15-4; body widthjust posterior to operculum 10-5-11-3, mean 10-8; least depth of caudal peduncle 9-0-9-5, mean9-2; dorsal fin base length 54-7-55-6, mean 55-0; first dorsal spine length 13-0-19-9, mean 16-6;second dorsal spine length 13-6-18-1, mean 16-3; third dorsal spine length 16-2-19-3, mean 17-3;fourth dorsal spine length 15-5-18-0, mean 16-8; anal fin base length 31-8-33-9, mean 32-7;pectoral fin length 19-9-22-7, mean 21-6; pelvic fin length 24-7-26-4, mean 25-4; caudal fin length36-7-40-1, mean 37-9. Small elongate fish, head and body moderately compressed. Mouth rather large, gape oblique,jaws nearly equal anteriorly, reaching posteriorly to a vertical through posterior margin ofpupil; upper lip as broad (vertically at front) as lower. Gill opening extending forwards ventrallyto a point vertically below hind margin, or just posterior to hind margin, of orbit. Upper jaw posteriorly with two series of fine, sharp, subconical teeth, about five series at 248 N. V. C. POLUNIN & R. LUBBOCK symphysis; outer series slightly larger and more caniniform posteriorly, increasingly so anteriorly;low notched ridge on vomer. Lower jaw posteriorly with one or two series of fine, sharp, sub-conical teeth, about five series at symphysis; outer series slightly larger and more caniniformposteriorly, increasingly so anteriorly, and with a single particularly enlarged caniniform toothanterolaterally on each side of jaw. Gill membranes rather narrowly attached at isthmus. Anterior and posterior nostrils separatedby space about equal to length of posterior nostril; posterior nostril round to oval, slightly largerthan round anterior nostril, separated from eye by space about equal to its length; anterior nostrilwith short membranous tube. Opercular edge entire, preopercular edge smooth. Scales cycloid anteriorly, becoming ctenoidlaterally approximately below third soft dorsal ray. Head naked; midline of nape not scaled.Dorsal and anal fins naked; pelvic fins mostly naked, a few embedded scales on base; pectoralfins mostly naked, possibly a few scales close to base; caudal fin with approximately basal sixthscaled. Sensory papillae moderately developed. Dorsal fin divided into two parts, not connected by membrane; first part with six spines, first,second, third and fourth spines longest; second part with a single spine followed by branchedrays. Origin of anal fin at a vertical through base of second dorsal soft ray. Posterior margins ofsecond dorsal and anal fins angular. Caudal fin rather pointed. Pectoral fins rounded, reachingabout nine-tenths of way to anal fin origin. Origin of pelvic fins below pectoral fin base; third andfourth pelvic soft rays longest (approximately equal in length in holotype, fourth ray longest inboth paratypes), reaching to or beyond anal fin origin, about four times as long as pelvic spine;fins united, with low fraenum over approximately basal fifth of fins. Colouration. In life, head and body pale grey to brownish, with 5 copper-coloured broad verticalbands and with scattered pale blue and orange spots; first band across part of predorsal areaand hind margin of operculum; second band from below fourth to sixth dorsal spines to justbehind pelvic fin base; third band from below second to fifth dorsal soft rays to bases of first tofourth anal soft rays; fourth band from below ninth to twelfth dorsal soft rays to bases of ninthto twelfth anal soft rays; fifth band on caudal peduncle. Pale blue spots mainly on preoperculum,operculum, and along dorsal profile of head and body; orange spots mainly on operculum, nape,and anterior part of body between first and second, and second and third vertical bands. Firstdorsal fin pale brownish with red spots edged with pale blue; second dorsal fin pale brownishwith broken horizontal pale blue lines and with two rows of orange spots, upper row along distalmargin of fin, lower row near base of fin; one bright red spot between penultimate and ultimatedorsal fin rays. Anal fin with brown base, separated from a horizontal submarginal red stripe bya band of pale blue; distal margin brownish, lined interiorly with pale blue. Pelvic fins brownishwith streaks of pale blue. Pectoral fins hyaline. Caudal fin pale brownish, darker basally, withbright red margin lined interiorly with pale blue dorsally and exteriorly with pale blue ventrally;up to about ten bright red spots edged with light blue, some of spots merging with red margin. In alcohol, head and body pale brown with bands largely discernible as areas of darker brown;orange and blue spots remain visible as pale spots, the former ringed with darker brown. Finsbrownish with markings usually visible as paler areas. REMARKS. Amblyeleotris latifasciata is close to A. aurora (Polunin & Lubbock, 1977) and A.sungami (Klausewitz, 1969). It can be distinguished from A. aurora by the number of soft analrays (13 in A. latifasciata; 14 in A. aurora), by certain morphometric characters (head length26-7-27-4% of S.L. in A. latifasciata, 23-2-26-5% in A. aurora; length of third dorsal spine16-2-19-3% of S.L. in A. latifasciata, 10-0-16-9% in A. aurora; length of caudal fin 36-7-40-1 %of S.L. in A. latifasciata, 27-4-34-5% in A. aurora}, and by colouration, notably the colour of thebody bands (coppery brown in A. latifasciata, pink in A. aurora). A. latifasciata is readily distin-guishable from A. sungami by the lateral scale count (87-92 in A. latifasciata; 102-108 in A.sungami) and by details of colouration; amongst the latter are to be noted the width of the bodybands (broad i n A. latifasciata; narrow in A. sungami), and the absence of an elaborate colourpattern on the caudal fin of A. sungami (present in A. latifasciata). A. sungami is only known NEW SPECIES OF THE GENUS AMBLYELEOTR1S 249 from the Red Sea, A. aurora from the Indian Ocean and A. latifasciata from the western PacificOcean. The Latin name latifasciata is derived from the words latus ( = broad) andfasciatus ( = banded)and refers to the breadth of the bands on the body, which serve to distinguish this species frommany related forms. HABITAT AND DISTRIBUTION. Amblyeleotris latifasciata is known from the Gulf of Thailand andthe Philippine Islands, where it was collected on sand and rubble at depths of 10-25 m; it livesin symbiosis with burrowing alpheid prawns. Acknowledgements For much advice on goby taxonomy we thank D. F. Hoese of the Australian Museum, Sydney.R. L. thanks Gray Cutlack and Brian Parkinson for help with fieldwork in Rabaul, and JohnnyKiener for help in Cebu. N. V. C. P. once more expresses gratitude to Nigel and Gwen Cornfieldfor facilities on the yacht Marimba. We are both grateful to Jeff Farrell, Jerry Welch and AdrianLamb, who all contributed greatly to the success of our collecting trip in Thailand. We thankP. J. P. Whitehead of the British Museum (Natural History) for reviewing the manuscript. References Polunin, N. V. C. & Lubbock, R. 1977. Prawn-associated gobies (Teleostei : Gobiidae) from the Seychelles,Western Indian Ocean : systematics and ecology. /. Zoo!., Land. 183 : 63-101. (in press). Notes on the gobies (Teleostei : Gobiidae) Amblyeleotris periophthalmus and Amblyeleotris fasciata. Rev.fr. Aquariol. Manuscript accepted for publication 19 July 1978. The taxonomy of Procavia capensis in Ethiopia, with special reference to the aberrant tusks of P. c. capillosa Brauer (Mammalia, Hyracoidea) G. B. Corbet British Museum (Natural History), Cromwell Road, London SW7 5BD Synopsis Procavia capensis capillosa from the Mendebo Mountains, Bale Province, Ethiopia is redescribed, drawingattention to the peculiar shape of the upper and lower incisors which are unique amongst the Hyracoidea.The characters and distribution of all the subspecies of P. capensis in Ethiopia are reviewed and theclassification of the genus discussed. Introduction Each of the two genera of rock hyraxes, Procavia and Heterohyrax (s.s.), comprises a series ofapparently allopatric forms covering a large part of Africa and, in the case of Procavia, theArabian Region. Both groups are notorious for the great amount of geographical variation, oftenof a very local nature and no doubt correlated with the high degree of isolation of suitable rockyhabitats. Although many forms have been described, no satisfactory comprehensive classificationexists for either group. Recent reviews are by Bothma (1971) and Roche (1972). Several Procavia collected in 1972 at high altitude in the Mendebo Mountains, western BaleProvince, Ethiopia by Dr D. W. Yalden, Dr P. A. Morris and Dr M. J. Largen appear referableto P. capensis capillosa Brauer, 1917 but show peculiarities of the upper and lower incisors thatset them apart from all other known specimens of Procavia and indeed of Hyracoidea. Thesefeatures were not, however, mentioned in the original description of capillosa, which was basedon a single female, and appear never to have been described. The upper tusks of normal male hyracoids are unparalleled in shape in any other mammalsand are remarkably constant throughout all three extant genera. The following numbers of malespecimens with permanent upper incisors have been examined without finding any deviation fromthe norm comparable to that seen in the specimens of capillosa: Procavia- 157, Heterohyraxs.s. - 80, Dendrohyrax - 89. The incisors of female P. c. capillosa are also distinctive but less sothan those of the males. Bothma (1971) recognized five species of Procavia but these have not been satisfactorily definedand I am inclined to accept the view of Roche (1972) that all should be considered conspecific.The variation thus included within one species is, however, rather extreme and much remainsto be done before it is adequately described. Although the character of the tusks sets capillosaapart from all other hyracoids, it seems unlikely that it would give rise to reproductive isolationand I therefore propose that subspecific rank is appropriate. Redescription of Procavia capensis capillosa Procavia erlangeri capillosa Brauer, 1917. Type locality Adaba ( = Agada), 700' N, 3924' E,western Bale Province, Ethiopia. Holotype: Zoologisch.es Museum, Berlin no. 21759, skin andskull (latter originally no. 21760) of an adult female, labelled 'Agada, 8. 11.01, Dr Ellenbeck'.The locality was given by Brauer as 'Agada am Abunass und Semaeno im Arussi Lande' butonly one specimen was detailed. The route map in Erlanger (1904) shows 'Adaba (Agada)' atthe locality shown on modern maps as Adaba. The type locality can therefore be restricted as Bull. Br. Mus. not. Hist. (Zool.) 36 (4) : 251-259 Issued 25 October 1979 251 252 G. B. CORBET above. Abunass probably refers to the locality of that name much further east at about 725' N,4025' E but there is no evidence that capillosa as here understood occurs there. SPECIMENS EXAMINED. The holotype skull; also the following, all from the Mendebo (Bale)Mountains, near Dinshu ( = Gurie), 706' N, 3947' E and up to 20 km westwards ('Shifta Rock'between Dinshu and Adaba), at altitudes from 3100 to 3500 m. All but the first two were foundas skulls and therefore were not sexed other than by the tusks. BMNH 1972.1078 ad. skull, skin BMNH 1972.1079 $ ad. skull, skin BMNH 1972.1080 ? ad. skull only BMNH 1972.1081 ? ad. skull only BMNH 1972.1082 [?] subad. skull only BMNH 1972.1083 ? ad. skull only BMNH 1972.1084 ? juv. skull only BMNH 1972.1077 [$] ad. skull only BMNH 1976.121 [?] ad. skull only BMNH 19', 6. 122 ? juv. skull only M 3 erupted, moderately worn M 3 erupted, moderately worn M 3 erupted, no mandibles, no incisors M 3 erupted, mandibles only M 2 erupted, complete M 3 erupted, no incisors P 1 " 4 only, no upper incisors M 3 erupting, no mandibles M 3 erupting, no mandibles P l -only DIAGNOSIS. Pelage long and dense; dorsal flash black; upper incisors of males and femalesconvergent, with flat anterior surfaces; lower incisors parallel; P x generally absent in adults;P 1 generally present and double-rooted. DESCRIPTION. Pelage long, dense and soft, containing many fine, wavy wool fibres (seen elsewherein the genus only in P. capensis mackinderi from comparable altitudes on Mount Kenya). Dorsalpelage creamy brown with dark grey hair-bases showing, giving an irregular mottled appearance(as in P.c. erlangeri but much less orange) rather than a neat agouti effect. Grey bases concealedmore effectively on nape, giving pale collar. Head darker than back, especially on cheeks andaround eyes, but much less dark than in P. c. erlangeri. Hairs around dorsal gland black, muchmore prominent than in P. c. erlangeribut rather less prominent than in P. c. scioana. Slight yellowspot on hind margin of black patch. Naked glandular area about 15-20 mm wide and 30-35 mmlong. Ventral pelage creamy buff, much less orange than in P. c. erlangeri, similar to P. c. scioanaand many other forms. Feet similar in colour to back. Vibrissae black, distributed as in otherProcavia. Skull differing from that of other Procavia in the following features (Fig. 1): upper incisors ofadult males convergent, with flat anterior surfaces; of adult female similar but smaller and lessangular, although much flatter and wider than in females of other subspecies; lower incisorsparallel in both sexes. The two adult male skulls also lack any ridge or overhanging crest on themaxilla below the anteroventral margin of the orbit (a condition normal in females elsewhere butrare in adult males). A three-pronged pectination of the lower incisors is visible on all four teethof the presumed female with M 2 erupted (1972.1082) but not on the much more worn teeth of thefully adult males. P 1 is lacking on both sides in one of the adult males (slightly the older judging by tooth-wearand cranial crests) but present and double-rooted in the other and in the four other fully adultskulls. In the subadult female it is present only on the left. Pj is lacking in all six adult or subadultmandibles, although single alveoli are present in one (M 3 erupted). In the holotype, a presumed female, the upper incisors are less convergent than in the others,leaving a gap of 2 mm between the tips, but they are nevertheless quite different in shape fromthose of either sex of other races. MEASUREMENTS (Table 1). Similar in size to other large forms of P. capensis, e.g. P. c. scioanaand P. c. erlangeri. Measurements of the only adult animal measured in the flesh (BMNH 1972.1079, c?, M 3moderately worn): head and body 555 mm; hind feet 75 mm; ear 35 mm; weight 4-25 kg. TAXONOMY OF PROCA VIA CAPENSIS b c 253 10 mm Fig. 1 Incisors of Procavia capensis from Ethiopia. Top: anterior view of upper incisors; centre: ventral view showing, in black, the upper incisors asthey would appear in transverse section at the alveoli; bottom: dorsal view of lower incisors,(a) P. c. capillosa, Bale Prov., adult c? (M 3 worn), BMNH 1972.1079; (b) P. c. erlangeri, Dire Dawa,Harar Prov., adult c? (M 3 worn), BMNH 34.11.20.8; (c) P. c. capillosa, Bale Prov., subadult ? (M 2erupted), BMNH 1972.1082; (d) P. c. erlangeri, Dire Dawa, Harar Prov., subadult ? (M 2 erupted),BMNH 34. 11. 20.6. HABITAT. Rocky outcrops between 3100 and 3500 m in Erica arborea andJuniperus zones muchdegraded by heavy grazing to a mosaic of grass and scrub (D. Yalden, in litt.). Variation of Procavia in Ethiopia The localities shown on the map (Fig. 2) represent the specimens of Procavia from Ethiopia inthe collection of the British Museum (Natural History) that are sufficiently localized, along withthe few others that have been seen or that have been reported in the literature in sufficient detail.A general distinction can be made between the high altitude forms, which are variable but large,dark and with a black or obscure dorsal flash, and the forms in the surrounding lowland savannaand steppe zones. These latter appear much more uniform than is suggested by the existing litera- 254 G. B. CORBET ^ o a 1 & 1111 s -D _^ J.0 a - 5 ^ -G 'O L_ CQ '5,_oIS LU i *3 " ^>_gr v> ^- "^^ 3 3 fe j3 i- U habe ^^ C U -0-5 TAXONOMY OF PROCAVIA CAPENSJS 255 36 "E Specimen examined O Published record 2000 m contour100km Fig. 2 The Ethiopian Highlands showing localities from which Procavia has been recorded. ture. A 'typical savanna' form can be recognized ranging from northern Tanzania (matschieiNeumann, 1900) through Kenya and Uganda, and across the savanna zone to Senegal, charac-terized especially by agouti pelage and large yellow dorsal flash. Unfortunately the older namesthat might apply to this form all relate to divergent peripheral populations - pallida Thomas,1891 (Somalia), latastei Thomas, 1892 (Senegal), kerstingi Matschie, 1899 (Dahomey). This formpenetrates Ethiopia from the south along the Rift Valley (specimens in BM(NH) from LakeLangano) where it can provisionally be called P. c.jacksoni Thomas, 1900; it probably also occurs 256 G. B. CORBET in the southeast (Ogaden) in the form of the very small P. c. pallida Thomas, 1891 ; and probablyextends from the west up the Blue Nile where it may be represented by P. c. meneliki Neumann,1902. In the north, the steppe/desert form resembles the savanna form except that the pelage is moreuniformly yellow-brown without marked agouti speckling, the head is not noticeably darkerthan the back and the dorsal flash, although yellow, is less conspicuous and contrasting. Thisform extends from Sudan north to Sinai and Lebanon and can be called P. c. syriaca withruficeps as a synonym - there is no case for using the name ruficeps (type-locality Dongola innorthern Sudan) for the more southern savanna form as is so often done, e.g. by Bothma (1971)and Roche (1972). This form probably occurs in northern Ethiopia and may intergrade with thenorthern highland form habessinica. In the south, on the other hand, it seems likely that the highaltitude forms are more isolated from the savanna forms by forest, although any such isolationmay well be breaking down with the destruction of forest. The characters of the four highland subspecies that can be recognized are summarized in Table1, along with those of P. c.jacksoni representing the savanna form. These subspecies are brieflyreviewed below together with intermediate populations from possibly isolated segments of theplateau. Highland forms P. c. habessinica (Hemprich & Ehrenberg, 1828)TYPE LOCALITY. Arkiko, near Massawa, N.E. Ethiopia. SYNONYMS. Euhyrax abyssinicus Gray, 1868; Hyrax alpini Gray, 1868; Hyrax ferruginea Gray,1869; Hyrax irroratus var. luteogaster Gray, 1869 (all from 'Abyssinia'); Procavia abyssinicaminor Thomas, 1892, Alali, Red Sea Coast, 13 N. REMARKS. This form can be recognized along the mountain chain between Massawa on thecoast and the region of Quiho and Antalo (1320' N) at altitudes up to 2500m. The presencein the dorsal flash of some hairs with extensive yellow tips makes it somewhat intermediatebetween scioana of the central highlands and syriaca in eastern Sudan, but the overall darkcolour and dark head are in clear contrast with the uniform yellowish brown of syriaca ( = burtoni).To the south, specimens from the Dessye region are intermediate in size and in the prominenceof the black dorsal flash between habessinica and the larger P. c. scioana. P. c. scioana (Giglioli, 1888)TYPE LOCALITY. Ankober, Shoa, central Ethiopia. SYNONYMS. Procavia shoana Thomas, 1892; ? Procavia butleri Wroughton, 1911, Jebel Fazogli,Blue Nile, Ethiopia/Sudan border. REMARKS. Found in the mountains of Shoa, around 3000 m, possibly forming a cline with thesmaller P. c. habessinica to the north. The few specimens seen from Gojjam, i.e. northwest of the Blue Nile Gorge, are similar butsmaller (condylobasal length of five adults 83-89 mm) and one of the eight skins has the dorsalflash brown rather than black. The form butleri has the dorsal flash black but indistinct and canbe considered a peripheral highland form. Specimens from the Arussi Mountains, i.e. southeast of the Rift Valley but north of the WebiShebeli, appear in some respects intermediate between P. c. scioana and P. c. capillosa. They arelarge (condylobasal length of the three adults measured 103, 105 and 109 mm, P J -M 3 44, 45,45 mm) and have the dorsal flash black but less prominent. One adult male (Field Museum 27090)has the upper incisors like those of capillosa in section although rather thicker, and parallel asin normal Procavia. Another adult male from the same locality, Tichu (c. 745' N, 3930' E),has the tusks normal in every respect. TAXONOMY OF PROCA VIA CAPENSIS 257 P. c. capillosa Brauer, 1917TYPE LOCALITY. Adaba, Mendebo Mts. REMARKS. This form may be isolated from that in the Arussi Mts to the north by the Webi Shebeliand is probably confined to the mountains of Bale Province. P. c. erlangeri Neumann, 1901 TYPE LOCALITY. Upper Webi Shebeli, especially around Harar, Ethiopia.SYNONYM. Procavia erlangeri comata Brauer, 1917, Gara Mulata Mts, west of Harar. REMARKS. The original description agrees well with specimens in the British Museum (NaturalHistory) from around Harar. The black head, yellowish colour and virtual absence of a dorsalflash make this a very distinctive form. The form comata was distinguished only by the greaterlength of the pelage, and can be considered consubspecific. Ingersol (1968) commented on theuniformity of specimens from a wide range of habitats in the Harar area. Lowland forms P. c. pallida Thomas, 1891TYPE LOCALITY. Hekebo Plateau, N. Somalia. REMARKS. A small form - condylobasal length of an adult female with M 3 worn 73-8 mm,P X -M 3 31-0 mm. The agouti pelage and yellow dorsal flash relate it to the savanna form. P. c. jacksoni Thomas, 1900TYPE LOCALITY. Ravine Station, Kenya. REMARKS. The sole fully adult specimen from the southern Rift Valley of Ethiopia (Lake Langano)has the dorsal flash prominent and yellow. The crown is slightly rufous, contrasting with the paleryellowish brown back with agouti speckling. This specimen was incorrectly called P. habessinicaalpini by Corbet & Yalden (1972). Specimens of jacksoni in Kenya are rather darker and havethe dorsal flash less prominent although comprising wholly yellow hairs. P. c. syriaca (Hemprich & Ehrenberg, 1828)TYPE LOCALITY. Mount Sinai. SYNONYMS. Hyrax ruficeps Hemprich & Ehrenberg, 1832, Dongola, N. Sudan; Hyrax burtoniGray, 1868, Egypt. REMARKS. This form occurs from the northern extremity of the range of the genus, in Lebanon,through Egypt and the Sudan, merging with the savanna form in southern Sudan (specimensfrom around Khartoum are intermediate), and possibly with P. c. habessinica in the hills ofextreme northern Ethiopia and eastern Sudan. Setzer (1956) postulated that two species weresympatric in northeastern Sudan, calling them P. habessinica burtoni and P. ruficeps ruficepsbut this appears to have been based on the variable allocation of old specimens from Dongolaon the Nile - there has never been a clear demonstration of sympatry of any two forms ofProcavia at one locality. Variation of Procavia throughout its range A more superficial examination of specimens from the entire range of the genus suggests thefollowing major groups, some of them with considerably modified local or peripheral variants. capensis - southern Africa; dorsal flash black; dorsal pelage finely speckled, head usuallyno darker than back; P l usually absent but present at the northeastern extremity (johnstoni,Malawi). 258 G. B. CORBET welwitschi - Angola/Namibia; dorsal flash yellow, P! usually absent. syriaca - savanna zone from northern Tanzania to Somalia and Senegal, and north throughSudan to Egypt, Sinai, Lebanon and Arabia; dorsal flash yellow, usually clearly defined; dorsalpelage agouti in savanna zone with head darker; more uniform yellowish brown north ofKhartoum with head no darker than back; P x usually present. Moderately differentiated formsoccur on the periphery: Mt Nimba, Mauritania, Hoggar, Jebel Marra, Mt Kenya, Somalia,Arabia. habessinica - Ethiopian plateau; dorsal flash black or obscure; not strongly agouti, head oftendark; P a variable; many local variations, some very close to capensis s.s. It is tempting to recognize these as discrete species but they are very difficult to diagnose. Inthe north the syriaca group appears to intergrade with the habessinica group in northern andperhaps western Ethiopia. There is a wide gap, from northern Tanzania to southern Malawi,apparently without Procavia. The widespread capensis s.s in southern Africa is scarcely dis-tinguishable from some members of the habessinica group, especially scioana from which itdiffers only in the usual absence of P a . The southwestern welwitschi seems discretely separablefrom the adjacent capensis but is only separable from some of the syriaca group by the absenceof P t which is not constant (Roche, 1972). The principal difference between this and previous classifications is the separation of matschiei(northern Tanzania) and other east African forms with the dorsal flash yellow from johnstoni(southern Malawi, dorsal flash black) which is here seen as a peripheral relative of the southerncapensis s.s. In spite of the great difference in external appearance and wide geographicalseparation these were considered conspecific (in a split classification) by Hahn (1934), followedby many other authors, mainly on the basis of well-developed P 1 . Heterohyrax in Ethiopia Heterohyrax brucei occurs throughout most of Ethiopia, sometimes occupying the same rockoutcrops as Procavia, and their separation in the field can be difficult. The most useful character-istics for recognizing Heterohyrax are: dorsal pelage short, neat, agouti; dorsal flash small,discrete, pale cream to rust-orange, hairs concolorous to roots; head scarcely darker than back;discrete pale streak above eye (Procavia sometimes has a more diffuse pale zone surrounding theeye or above and behind the eye); ventral pelage grey, less yellowish than in Procavia. Size isnever so great as in the large forms of Procavia (rarely over 480 mm head and body) but coloniesof one species show a great range of sizes at any one time due to slow attainment of full adult size.In the hand the clearest external distinction in adult males is the anterior position of the penis inHeterohyrax - about 60-70 mm in front of the anus compared with 20-30 mm in Procavia. Immature skulls can be difficult to distinguish but adult skulls of Heterohyrax have the teethrather uniform in size, with the combined length of M J -M 3 shorter than P 1 -? 4 whereas in ProcaviaMi-M 3 are conspicuously large and together considerably larger than P 1 -? 4 . Summary 1. Procavia capensis capillosa from the Mendebo Mts, Bale Province, Ethiopia is distinguishablefrom P. c. scioana to the north and P. c. erlangeri to the northeast by its woolly pelage and fromthese and all other hyracoids by the formation of the incisors - uppers convergent, with flatanterior surfaces in both sexes, lowers parallel (consistent, allowing for sexual dimorphism,amongst all seven specimens). 2. The forms erlangeri, capillosa, scioana and habessinica form a distinctive, although variable,group in the Ethiopian Highlands with the last showing characters approaching the adjacentlowland P. c. syriaca. 3. Four main regional groups are recognized in P. capensis, distinguished by overall colour ofthe dorsal pelage and especially of the 'dorsal flash' around the mid-dorsal gland: capensis s.s.and welwitschi in southern Africa, syriaca in the northern savanna and arid zones and habessinicain the Ethiopian highlands. TAXONOMY OF PROCA VIA CAPENSIS 259 Acknowledgements I wish to thank Dr M. J. Largen, Dr P. M. Morris and Dr D. W. Yalden for presenting theirEthiopian collections to the British Museum (Natural History) and for help and guidance withlocalities; Miss Daphne Hills for curatorial assistance; the authorities and curators of thefollowing museums for facilitating examination of their collections: Field Museum (Chicago),U.S. National Museum of Natural History (Washington); and Dr R. Angermann and Dr H.Hackethal of the Zoologisches Museum, Berlin for information on P. c. capillosa and the loanof a specimen. Dr Yalden provided helpful criticism of the manuscript. References References to original descriptions can be found in Allen (1939). Allen, G. M. 1939. A checklist of African mammals. Bull. Mus. comp. Zool. 83 : 1-763. Bothnia, J. du P. 1971. Part 12, order Hyracoidea, 8 pp. In Meester, J. & Setzer, H. W. (eds) The mammals of Africa: an identification manual. Washington. Brauer, A. 1917. Neue Procaviiden. Sber. Ges. naturf. Freunde Berl. : 294-303.Corbet, G. B. & Yalden, D. W. 1972. Recent records of mammals (other than bats) from Ethiopia. Bull. Br. Mus. nat. Hist. (Zool.) 22 : 211-252. Erlanger, C. F. von 1904. Beitrage zur Vogelfauna Nordostafrikas. /. Orn. 52 : 137-244, maps 1-3.Hahn, H. 1934. Die Familie der Procaviidae. Z. Sdugetierk. 9 : 207-358.Ingersol, R. H. 1968. The ecological significance of mammals in the eastern Chercher Highlands of Harar Province, Ethiopia. Ph.D. thesis, Oklahoma State University. Roche, J. 1972. Systematique du genre Procavia et des damans en general. Mammalia 36 : 22-49.Setzer, H. W. 1956. Mammals of the Anglo-Egyptian Sudan. Proc. U.S. nat. Mus. 106 : 447-587. Manuscript accepted for publication 16 June 1978. British Museum (Natural History)Monographs British Marine Amphipoda : Gammaridea By R. J. Lincoln 658pp 2300 figures October 1979 50 An Atlas of Freshwater Testate Amoebae By C. G. Ogden & R. H. Hedley 222pp 95 plates January 1980 17.50 Handbooks British Crabs By R. W. Ingle Approx 240pp 34H/T 31 line illus. Spring 1980 16,00 Lists of all BM(NH) publications are available free on request to : Publications SalesBritish Museum (Natural History)Cromwell RoadLondon SW7 5BD Titles to be published in Volume 36 A guide to the species of the genus Aspidisca.By Irene C. H. Wu & C. R. Curds. The Hemiuroidea : terminology, systematics and evolution.By D. I. Gibson & R. A. Bray. Notes on the anatomy of Macrochirichthys macrochirusValenciennes, 1844, with comments on the Cultrinae (Pisces,Cyprinidae). By G. J. Howes. Miscellanea Anatomy, relationships and classification of the familiesCitharinidae and Distichodontidae (Pisces, Characoidea).By R. P. Vari. Printed by Henry Ling Ltd, Dorchester Bulletin of the British Museum (Natural History) Anatomy, relationships and classificationof the families Citharinidae andDistichodontidae (Pisces, Characoidea) Richard Peter Vari Zoology series Vol 36 No 5 29 November 1979 The Bulletin of the British Museum (Natural History), instituted in 1949, is issued in fourscientific series, Botany, Entomology, Geology (incorporating Mineralogy) and Zoology, andan Historical series. Papers in the Bulletin are primarily the results of research carried out on the unique andever-growing collections of the Museum, both by the scientific staff of the Museum and byspecialists from elsewhere who make use of the Museum's resources. Many of the papers areworks of reference that will remain indispensable for years to come. 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Trustees of the British Museum (Natural History), 1979 This number completes Volume 36 ISSN 0007-1498 Zoology series Vol 36 No 5 pp 261-344British Museum (Natural History)Cromwell RoadLondon SW7 5BD Issued 29 November 1979 f Anatomy, relationships and classification of thefamilies Citharinidae and Distichodontidae (Pisces,Characoidea) Richard Peter Vari NATO Postdoctoral Fellow, Department of Zoology, British Museum (Natural History),Cromwell Road, London, SW7 5BD 1 Contents Synopsis ........... 261 Introduction ........... 262 Methods ........... 264 Materials ........... 264 Abbreviations used in text figures ....... 265 Nomenclatural comments ......... 265 Phylogenetic analysis ......... 266 Jaws ........... 266 Dentition ........... 275 Supraethmoid .......... 277 Anterior orbital region ......... 279 Posterior orbital and anterior otic regions ...... 283 Occipital region ... . . . . . . . . 289 Cranial fontanelle ......... 290 Suspensorium .......... 290 Opercle ........... 295 Dermosphenotic, pterotic and suprapreopercle ..... 296 Supraorbital and infraorbitals ........ 301 Branchial apparatus ......... 303 Weberian apparatus . . . . . . . . . 305 Postcleithra .......... 310 Pelvic bone . . . . . . . . . .311 Caudal skeleton . . . . . . . . . .311 Scale form . . . . . . . . . .313 Myology ........... 315 Swimbladder, intestinal and epibranchial organ forms .... 321 Olfactory bulbs .......... 322 Phylogenetic reconstruction ........ 324 Families Citharinidae and Distichodontidae ...... 324 Family Citharinidae ......... 326 Family Distichodontidae ........ 327 Conclusions ........... 339 Comparisons with previous classifications ...... 340 Comments on the African Characidae ....... 341 Acknowledgements .......... 342 References ........... 342 Synopsis Various osteological and soft anatomical systems in the families Citharinidae and Distichodontidae wereexamined to test: the hypothesized monophyly of the unit formed by citharinids and distichodontids Present address: Division of Fishes, Department of Vertebrate Zoology, National Museum of Natural History,Smithsonian Institution, Washington D.C. Bull. Br. Mus. nat. Hist. (Zool.) 36 (2) : 261-344 Issued 29 November 1979 261 262 R. P. VARI within characoids; the interrelationships of the nominal genera within these families; and the monophylyof the nominal genera and suprageneric taxa. The evidence of this study is congruent with the hypothesis that citharinids and distichodontids form amonophyletic subunit of characoids definable by a series of derived characters. However, the arrivedat hypothesis of generic interrelationships necessitates several modifications of the previous generic andsuprageneric taxonomy of these families. The retention of the previously recognized family Ichthyboridaewas found to result in a non-monophyletic family Distichodontidae. Consequently, the Ichthyboridaeof earlier workers is sunk into the Distichodontidae. At the generic level, Congocharax and Dundocharaxare placed into synonymy of Neolebias, and Gavialocharax and Phagoborus are synonymized intoIchthyborus. These changes resolve the previously non-monophyletic natures of Neolebias and Phagoborusrespectively. The conclusions of this study contraindicate the monophyly of the genus Distichodusas presently defined, and cast doubt on the monophyletic nature of Hemigrammocharax and Nannocharax.These three genera are, nonetheless, tentatively retained until such time as an analysis of the phylogenyof their contained species can be undertaken. Finally, information uncovered during this study supports the concept of the monophyletic nature ofthe subunit of characoids formed by the African Characidae. However, the available evidence alsoindicates that as presently constituted the genus Alestes is non-monophyletic. This taxon is, however,retained until an indepth analysis of African characids permits its redefinition on the basis of derivedcharacters. The subdivision of the African Characidae into the subfamilies Hydrocyninae and Alestiinaeresults in the latter taxon being non-monophyletic. Consequently the Hydrocyninae is sunk into theAlestiinae, which in this broader sense now constitutes a monophyletic unit. Introduction The superfamily Characoidea (Rosen & Greenwood, 1970) is one of the largest groups in theichthyofauna of the Neotropical region and Africa, and one of the major freshwater fish assem-blages. Although the classification of the superfamily has undergone extensive revision duringthe last century, questions on the interrelationships of characoids at all taxonomic levels remainlargely unresolved. This paper deals with the relationships between and to a lesser extent withinthe genera which constitute the African endemic characoid families Citharinidae and Disticho-dontidae. A series of workers including Boulenger (1909), Regan (1911) and Gregory & Conrad (1938)have suggested that citharinids and distichodontids form a closely related subunit of characoids,with Regan (1911, p. 22) terming them 'a very natural group of African Fish'. AlthoughGreenwood et al. (1966) did not deal with interfamilial relationships within the Characoidea, theydo list these families sequentially, a procedure meant to indicate close relationship (Weitzman,pers. commun., in Roberts, 1969, p. 399). Despite this broad consensus, the basis for the hypo-thesized close relationship of these families has remained obscure. Furthermore, as shown inTable 1 the number and limits of the suprageneric taxa recognized within the families Citharinidaeand Distichodontidae have been subject to considerable differences of opinion. The conflictingnature of these classifications is reflected in the history of the group recognized as the subfamilyDistichodontinae by Boulenger (1909) and more recently as the family Distichodontidae byGreenwood et al. (1966) (both of these concepts differ from the Distichodontidae of this work, seep. 265). This assemblage was subdivided into two subfamilies with different limits by Eigenmann(1909) and Regan (1911). Subsequently, Gregory & Conrad (1938) removed the distichodontidgenera Xenocharax, Neolebias, Hemistichodus and Nannaethiops to their subfamily Citharininae.More recently Poll (1973) carried this trend further by placing all distichodontids (sensuGreenwood et al., 1966) into his family Citharinidae. Monod (1950), in turn, defined the supra-generic taxa among citharinids and distichodontids in such a manner as to exclude the disticho-dontid genera Xenocharax, Neolebias, Nannaethiops and Paradistichodus from all of hissubfamilies. To the extent that these authors used their classifications as a mode of conveyingconcepts on the relationships between taxa, such differing classifications reflect the uncertaintythat exists concerning the phylogenetic history of citharinids and distichodontids. This uncertainty was a consequence of a series of factors, three of which appear to have beenof paramount importance. Firstly, earlier classifications were based on a limited number of CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 263 Table 1 Previous classifications of the families Citharinidae and Distichodontidae with members of thesuprageneric units listed where originally specified Boulenger, 1909 Eigenmann, 1909 Regan, 1911 Gregory & Conrad, 1938 Greenwood et al., 1966Poll, 1973 CitharininaeDistichodontinae Ichthyborinae Citharininae Neolebiinae Distichodontinae Phaginae Ichthyborinae Citharininae Xenocharacinae Distichodontinae Hemistichodinae Ichthyborinae CitharininaeDistichodontinae Citharinidae Distichodontidae Ichthyboridae Citharinidae Ichthyboridae Citkarinus, Citharidium Nannaethiops, Neolebias, Distichodus, Nanno-charax, Xenocharax Ichthyborus, Neoborus ( = Phagoborus), Meso-borus, Eugnatichthys, Paraphago, Phago Citharinus, Citharidium Xenocharax, Nannaethiops, Neolebias Distichodus, Nannocharax Hemistichodus Ichthyborus, Neoborus { = Phagoborus), Meso- borus, Eugnatichthys, Paraphago, Phago Citharinus, Citharidium, Xenocharax, Nan-naethiops, Neolebias, HemistichodusDistichodus, Nannocharax, Ichthyborus, Meso-borus, Phagoborus, Eugnatichthys, Paraphago,Phago Citharinus, Citharidium, Xenocharax, Neo-lebias, Nannaethiops, Dundocharax, Congo-charax ?, Paradistichodus, Distichodus, Nan-nocharax, HemigrammocharaxIchthyborus, Phagoborus, Gavialocharax, Hemi-stichodus, Microstomatichthyoborus, Meso-borus, Eugnatichthys, Paraphago, Phago,Belonophago primarily external characters. The utility of the limited information available from these systemswas, however, reduced by several misinterpretations of characters and character states. Secondly,the small size of many distichodontid species resulted in a series of errors in character statedetermination. These errors were especially prevalent in the description of tooth form and dis-tribution; characters which, nonetheless, were weighed heavily by many workers. Finally, andperhaps most importantly, generic and suprageneric taxa were defined on the basis of primitiveor combinations of primitive and derived characters, a procedure which often failed to definemonophyletic groups. The present study attempts to determine the phylogenetic relationships, both at the genericand suprageneric levels, within the subunit of characoids formed by the families Citharinidae andDistichodontidae. The phylogenetic reconstruction is based primarily on osteological characters,although myological and other soft anatomical systems are also utilized. The three main objectivesof this study are: (1) to test the hypothesis of the monophyletic nature of the unit formed bycitharinids and distichodontids within characoids; (2) to determine the interrelationships of thegenera within these families; and (3) to define the various generic and suprageneric taxa on thebasis of shared derived characters. 264 R. P. VARI Methods Relationships between and within the families Citharinidae and Distichodontidae are evaluatedusing the methods of phylogenetic analysis first described in detail by Hennig (1966). Thesemethods along with the two predominant alternative methodologies (numerical taxonomy andevolutionary biological classification) have been and continue to be a source of controversy withrespect to their relative merits. However, the author feels that the Hennigian methodology bestsuits the aims of this study - the erection of an hypothesis of the evolutionary relationships of thegroups in question. In using the Hennigian or cladistic methodology, certain principles are followed: recognizedtaxa must be monophyletic in that they include all descendants of a hypothesized commonancestor (the concept of monophyly advanced by the evolutionary biological school, in contrast,does not require the inclusion in a taxon of all descendants of a common ancestor). Monophyleticgroups are defined on the basis of shared derived (synapomorphic) characters which are con-sidered to be the only type of characters valid for the erection of a hypothesis of common ancestry.In contrast, shared primitive (symplesiomorphic) characters and estimated degrees of similarityor difference are not utilized for the analysis of interrelationships. Species or species groups(two or more species forming a monophyletic unit) hypothesized to have had a common ancestorare termed sister species or sister groups. A derived (apomorphic) character used for the definitionof a sister group relationship cannot serve for the definition of the contained taxa in either of thesister groups since it is primitive (plesiomorphic) at the level of the included subtaxa. As discussed by Nelson (1973a &b), the apomorphic or plesiomorphic nature of characterscan be evaluated by two methods. The first of these, outgroup comparisons, involves the examina-tion of the state of the character in a variety of other groups in order to determine which of therelevant character states is probably primitive. For the purposes of this study, outgroup com-parisons were carried out on representatives of other characoid families and selected non-characoid ostariophysans. The second method of character polarity determination involvesinformation available from ontogenetic transitions. If in two sister groups X and Y, the speciesof group X undergo an ontogenetic transition in character A from state A to state A', a transitionthat does not occur in the species of group Y, then two explanations exist for the distribution ofthe transition: (1) that the transition (state A to A') was not present in the common ancestor ofX and Y, but rather arose in lineage X; or (2) that the transition was present in the commonancestor of X and Y, but was secondarily lost in lineage Y. Comparing these hypotheses, we findthat the first makes a single assumption; that of the acquisition of the transition in group X.The second in contrast, makes two assumptions, that of the presence of the transition in thecommon ancestor of groups X and Y, and a second assumption of its subsequent loss in lineageY. If we accept a parsimony criterion for the evaluation of the preferability of alternative hypo-theses, then the first, more parsimonious, hypothesis is preferable. Consequently, in this study,ontogenetic transitions (ontogenetic shifts from state A to state A') are considered to indicatephylogenetic polarity (state A' is considered apomorphic with respect to state A). In the following discussion, osteological terminology follows Weitzman (1962) with severalexceptions. As noted by Roberts (1969) vomer is substituted for prevomer and intercalar foropisthotic. Furthermore, I follow Patterson (1975) in using epioccipital rather than epiotic, andsupraethmoid rather than ethmoid, and follow Nelson (1973c) in substituting angulo-articularfor articular, and retroarticular for angular. Myological terminology is that of Winterbottom(1974). All drawings were made using a Wild M5 drawing tube. Details were added freehand underhigher magnification. Myological drawings are based on dissections of the right side of thespecimen and are reversed into conventional orientation. Materials Osteological and soft anatomical systems were examined on alcohol preserved material, dryskeletons, and cleared, alizarin-stained specimens of representative species of the citharinid genera CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 265 Citharinus and Citharidium and the distichodontid genera Xenocharax, Neolebias, Nannaethiops,Paradistichodus, Distichodus, Nannocharax, Hemigrammocharax, Hemistichodus, Ichthyboms,Microstomatichthyoborus, Mesoborus, Eugnatichthys, Phago and Belonophago. In the case of themonotypic distichodontid genus Paraphago, known only from the syntypic series, only osteologicalcharacters revealed by radiographs and external anatomy could be examined. Comparative studieswere carried out on representatives of all other African and Neotropical characoid families andfor certain characters on examples of the major non-characoid ostariophysan groups, bothotophysan and anotophysan. A detailed listing of this extensive material would add little to thepaper. Rather, a list of material examined, both skeletal and whole, quoting museum cataloguenumbers, is deposited in the Fish Section and General Library of the British Museum (NaturalHistory). Abbreviations used in text figures At A! division of the adductor mandibulae max muscle o A 2-1 lateral portion of the A 2 division of the ops adductor mandibulae orb A 2 -m medial portion of the A 2 division of the os adductor mandibulae par A 3 A 3 division of the adductor mandibulae para A w intramandibular (A w ) division of the pb adductor mandibulae pc aa angulo-articular pel ac anterior chamber of swimbladder pdg ant antorbital pel bo basioccipital ph cca canal for coeliac artery pip cl cleithrum pmp cts connective tissue sheath pmx den dentary pop DOP Dilatator operculi muscle pro dph dorsal process of hyomandibula psc ds dermosphenotic ptf e epibranchial pto ep epural pts epi epioccipital q ex exoccipital ra fr frontal rt h hypural soc hyf hyomandibular fossa sor hyo hyomandibula sph io infraorbital spo ico independent coeliac ossification T ip ischiac process ti LAP levator arcus palatini muscle up le lateral ethmoid ur les lateral ethmoid strut vpv LP ligamentum primordiale maxilla opercle opercular spine orbitosphenoid os suspensorium parietal parasphenoid pharyngobranchial posterior chamber of swimbladder postcleithrum posterolateral dentary groove pelvic bone parhypural posterolateral preopercular process posteromedial preopercular process premaxilla preopercle prootic pterotic sensory canal posttemporal fossa pterotic pterosphenoid quadrate retroarticular replacement teeth supraoccipital supraorbital sphenotic suprapreopercle tendon terminal section of intestine upper pharyngeal tooth plate uroneural ventral process of vertebra Nomenclatural comments The conclusions of this study necessitate several changes in the previous generic and supragenericclassifications within the family Distichodontidae. In so far as the modified terminology is usedthroughout the following discussion, these changes are briefly summarized at this point. Within recent years, most workers have recognized two subfamilies (Distichodontinae andIchthyborinae) or families (Distichodontidae and Ichthyboridae) for the unit termed the family 266 R. P. VARI Distichodontidae in this work. However, the retention of both taxa as previously defined wasfound to be untenable under the taxonomic procedures adopted as a basis for this study. Ratheronly a single suprageneric taxon, the family Distichodontidae, is recognized to contain the speciespreviously divided between the Distichodontidae and Ichthyboridae of Greenwood et al. (1966)and the subfamilies Distichodontinae and Ichthyborinae of many other recent workers. Similarly,the genera Dundocharax and Congocharax are placed as synonyms of Neolebias, with Dundocharaxbidentatus, Congocharax gossei, C. spilotaenia and C. olbrechtsi hereafter termed Neolebias bi-dentatus, N. gossei, N. spilotaenia and N. olbrechtsi respectively. Finally, both Gavialocharax andPhagoborus are placed as synonyms of Ichthyborus, with Gavialocharax monodi, Phagoborusornatus and P. quadrilineatus hereafter referred to as Ichthyborus monodi, I. ornatus and /.quadrilineatus respectively. Phylogenetic analysis The analysis of the phylogenetic relationships of the genera and suprageneric units within thecomplex formed by the families Citharinidae and Distichodontidae is divided into two sections.The first part of the analysis deals with the relevant characters in the various anatomical systemsexamined, along with a discussion of the basis for their hypothesized polarity within characoids.In the second portion of the analysis the evidence from these characters is incorporated into areconstruction of the hypothesized most parsimonious phylogeny of the genera within thesefamilies. It should be emphasized that it is not the purpose of this study to provide detailedanatomical descriptions of the osteology and soft anatomy of all citharinid and distichodontidgenera. Rather, only those characters used in the phylogenetic reconstruction are discussed. Jaws A series of modifications of the upper and lower jaws distinguish the unit formed by theCitharinidae and Distichodontidae within characoids and unite groups of varying levels ofuniversality within this complex. The following discussion will deal firstly with the hypothesizedderived characters common to the upper and lower jaws; secondly, with those limited to thelower jaw; and finally, with those of the upper jaw. Dental characters of phylogenetic interest arediscussed separately in the following section. Replacement tooth trenches The form of the dentary and premaxillary replacement tooth trenches exhibits several characterstates among citharinids and distichodontids. In Xenocharax (Fig. la) the dentary and premaxillaare solid basally, with the replacement tooth trenches having the form of relatively shallowgrooves, not or only slightly open to their partners across the symphyses. Such a trench form isclose to the generalized and probably plesiomorphous characoid condition and is thus consideredto represent the least derived state of this character within citharinids and distichodontids. Twomajor modifications of the Xenocharax form of replacement tooth trench occur in these families,one shared by most distichodontids and the other unique to citharinids. The distichodontid genera Nannaethiops and Neolebias share with Xenocharax the plesio-morphous condition of shallow premaxillary and dentary replacement tooth trenches. In allother distichodontids, in contrast, the trenches are expanded, bulbous cavities, broadly open totheir partners across the symphysis (Fig. Ib.) The expansion of the trenches into the primitivelysolid centres of the premaxilla and dentary both provides an increased surface for the attachmentof the pleurodont dentition common to these genera, and space for their multiple rows ofreplacement teeth. Such a greatly expanded replacement tooth trench would appear to be uniqueto and apomorphous for these genera among characoids. In contrast, the greatly expandedtrenches of the Neotropical characoid family Parodontidae differ from the above in being limitedto the premaxilla, in not being open to each other across the symphyses, and in having thereplacement tooth series separated by bony partitions. Similarly, the broad replacement toothtrenches of the Anostomidae fail to open to their partners symphyseally. CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 267 A second mode of expanded replacement tooth trench characterizes the family Citharinidae.In Citharinus and Citharidium the trenches are widened along the primitively horizontal planeof the dentaries and premaxillae to form broad shallow grooves. More significantly, the replace-ment tooth trenches of both jaws are rotated outwards relative to the Xenocharax condition.This reorientation is especially pronounced in the lower jaw where it has resulted in the shift of theprimitively distal, anterior ridge of the trench to the outer surface of the dentary, and theformation of the distal edge of the lower jaw by the posterior ridge of the replacement toothtrench. Such a reorientation and broadening of the trenches appears to be unique to and auta-pomorphous for the Citharinidae among Characoids. rt Fig. 1 Sagittal section through the dentary symphysis of A. Xenocharax spilurus, B. Distichodus brevipinnis, C. Ichthyborus quadrilineatus. Lower jaw A series of modifications of the dentary and of the articulation between the dentary and angulo-articular characterize various assemblages among citharinids and distichodontids. One of thedistinctive characters in the lower jaws of these families is their common lack of the bony inter-digitating symphyseal processes that interconnect the dentaries of most characoids. Such dentaryinterdigitations form a hinge permitting horizontal pivoting of the dentaries about the symphysisbut reducing or eliminating twisting of the bones with respect to each other. This symphysealdentary hinge ranges in complexity from the rather simple processes common to many tetra-gonopterines, to the massive interlocking systems in Hydrocynus (Gregory & Conrad, 1936)and the Cynodontini (Nelson, 1949). An interdigitating symphyseal dentary hinge is widespreadamong characoids and is found in the Hepsetidae, the family that has been considered to be themost 'primitive' living member of the Characoidea (Roberts, 1969, p. 442). If Hepsetus is indeedthe sister group to other characoids, its possession of the dentary hinge along with the widespreaddistribution of this character within the Characoidea would indicate that an interdigitatingsymphyseal dentary hinge is plesiomorphous for characoids. The lack of such a joint would thenbe a apomorphous secondary loss. It should be emphasized, however, that the phylogeneticplacement of hepsetids has not been satisfactorily resolved. Furthermore, an interdigitatingdentary symphyseal joint is also lacking in the Neotropical characoid families Curimatidae,Hemiodontidae, Prochilodontidae, Anostomidae, Chilodontidae and Parodontidae. Be that as itmay, at the least, the common lack of the interdigitating symphyseal dentary hinge in citharinidsand distichodontids is consistent with the hypothesized monophyletic nature of the unit that theyform within characoids. Although the lack of an interdigitating dentary symphyseal hinge is common to all citharinidsand distichodontids, the exact form of the interdentary articulation varies within these families.Citharinids and the distichodontid genera Xenocharax, Neolebias, Nannaethiops, Paradistichodus,Distichodus, Nannocharax, Hemigrammocharax and Hemistichodus have a solely syndesmoticarticulation between the dentaries. Within this assemblage, in Citharinus, Citharidium, Xeno-charax, Nannaethiops and Neolebias the combination of the relatively limited contact of the 268 R. P. VARI dentaries across the symphysis and the syndesmotic joint permits a slight mobility of the dentariesrelative to each other. In contrast, Paradistichodus, Distichodus, Nannocharax, Hemigrammocharaxand Hemistichodus have an immobile though syndesmotic interdentary joint as a consequenceof their expanded replacement tooth trenches and the resultant greater cross-sectional contactacross the symphysis. This union of the dentaries is further developed in some larger individualsof Distichodus lussso and D. brevipinnis which have irregular interdigitations between thedentaries (see Daget, 1959, Fig. 5). The dentaries in the distichodontid genera Ichthyborus, Microstomatichthyoborus, Mesoborus,Eugnatichthys, Paraphago, Phago and Belonophago are synarthritically immovably interconnectedin either of two ways. In Ichthyborus this union takes the form of a symphyseal fusion of thedentaries, an adaptation which provides a firm implantation for the enlarged median canine thatcharacterizes this genus. Microstomatichthyoborus, Mesoborus, Eugnatichthys, Belonophago,Paraphago and Phago, alternately, have a series of bony interdigitations uniting the dentaries. 1mm Fig. 2 Nannocharax niloticus, dentaries, ventral view. These interdigitations differ, however, from those forming the symphyseal dentary hinge of mostcharacoids both in their location at the rear of the dentary symphysis and in rendering thedentaries totally immobile relative to each other. Both this synarthritic dentary articulation andthe fused dentaries of Ichthyborus appear to be unique to their possessors among characoids andindicative of the monophyletic nature of each of these assemblages. Various modifications of the dentary serve to distinguish subunits within the family Dis-tichodontidae. The genera Hemigrammocharax and Nannocharax are characterized by apronounced posteriorly-directed process arising from the posteroventral edge of the dentaryslightly lateral to the dentary symphysis (Fig. 2). This process, which serves as the point ofattachment for the protractor hyoidei muscles, is unique to these genera among the characoidsexamined and is thus hypothesized to be apomorphous. Hemistichodus, Ichthyborus, Micro-stomatichthyoborus, Mesoborus, Eugnatichthys, Paraphago, Phago and Belonophago, in turn,have a prominent dorsally-directed posterodorsal dentary ramus that is laterally overlapped by,and tightly joined to, the closely connected maxilla and premaxilla common to these genera. Sucha posterodorsal ramus of the dentary (Figs 3c & d) contrasts with the hypothesized plesiomorphousdorsally straight-edged process common to most characoids (Fig. 3a). Outgroup comparisonshave failed to reveal any other charcoid group with such a pronounced development of thisprocess. Thus the prominent posterodorsal ramus of the dentary common to these distichodontidsis considered derived. Further adaptations of this dentary ramus characterize less universal subunits of the Disticho-dontidae. In Hemistichodus this posterodorsal dentary ramus is autapomorphically furtherenlarged into an elongate, inwardly curved process passing medial to the premaxilla (see Daget,1968, Fig. 2). Eugnatichthys, Paraphago, Phago (Fig. 3d) and Belonophago, in turn, have thelateral face of the ramus restructured to form a shallow groove articulating with the roundedposteroventral portion of the maxilla characteristic of these genera. This alteration of the dentaryin conjunction with a series of modifications of the maxilla forms a sliding joint between theupper and lower jaws during jaw movements. CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 269 den ra den den aa ra Fig. 3 Lower jaws of A. Xenocharax spilurus, B. Distichodusnotospilus, C. Ichthyborusquadrilineatus,D. Phago intermedius, left lateral view. The greatest morphological variation in the lower jaw of the families Citharinidae andDistichodontidae involves the form of the articulation of the dentary with the angulo-articular.In Xenocharax (Fig. 3a) the angulo-articular and dentary meet along an elongate triangular jointwith the posteroventral process of the dentary bearing a lengthy mandibular sensory canalsegment. The tight fit of this joint and the strong connective tissue bands across the articulationimmovably join the dentary and angulo-articular into a single functional unit. Thus in Xeno-charax all motion of the dentary relative to the suspensorium is a consequence of the mobilitybetween the angulo-articular and quadrate. This form of articulation is generalized for characoidsand most teleosts (see Nelson, 1973c), and undoubtedly represents the plesiomorphous conditionfor the Citharinidae and Distichodontidae. Such an immobile articulation is common tocitharinids and the distichodontid genera Xenocharax, Neolebias, Nannaethiops and Paradisti-chodus. All other distichodontid genera, in contrast, have a mobile joint between the angulo-articular and dentary. The least restructured form of the articulation is found in Hemistichoduswhich retains the plesiomorphous insertion of the triangular anterior process of the angulo-articular into a notch formed by posterodorsal and posteroventral dentary processes. However,in contrast to the primitive condition, the dentary in Hemistichodus is not in tight contact withthe anterior process of the angulo-articular and the connective tissue bands joining these bonesare flexible. These modifications result in a limited mobility between the dentary and angulo-articular. Such motion approximates the hypothesized first stage in the phylogenetic developmentof the more mobile Distichodus, Ichthyborus and Mesoborus types of articulations between thesebones. The second form of mobile joint between the dentary and the angulo-articular, the Distichodustype (Fig. 3b) is synapomorphous for Distichodus, Nannocharax and Hemigrammocharax amongcharacoids. In these genera the primitively elongate dentary is horizontally foreshortened and itsposteroventral process greatly reduced. Furthermore, the axis of the body of the dentary isreorientated distinctly anteroventrally from the horizontal or anterodorsal orientation common 270 R. P- VARI to most characoids. This reorientation, which shifts the plesiomorphously anterior face of thedentary posteroventrally, is particularly pronounced in bottom-dwelling Nannocharax specieswhich have a nearly vertical axis through the body of the dentary. An additional consequence ofthis dentary foreshortening and reorientation is the reduction of the dentary portion of themandibular sensory canal in Distichodus and its loss in Nannocharax and Hemigrammocharax. Congruent with these dentary alterations are a series of modifications of the angulo-articularand of its relationship to the dentary. In the Distichodus type lower jaw, the angulo-articular isexpanded dorsally or anterodorsally into a large flat plate which lies along and is ligamentouslymovably attached to the medial face of the dentary. These alterations in angular-articular formand position together with the previously described dentary modifications result in a highlymobile joint between the dentary and angulo-articular, in addition to the usual mobility of thelatter on the quadrate. This mode of articulation of these elements, the 'chevauchement lateral'of Monod (1950), along with the previously described reorientation of the dentary permits amarked degree of horizontal motion of the dentary. The two final forms of mobile articulation between the dentary and angulo-articular, theIchthyborus and Mesoborus types, share several derived characters. In both of these lower jawforms the posteroventral ramus of the dentary is lacking as a distinct process contrary to itsplesiomorphous elongate form. Congruent with this change in dentary structure is an anteriorexpansion of the angulo-articular and its shift onto the medial surface of the dentary. Such anexpansion, which compensates for the loss of support primitively provided by the posteroventraldentary ramus, differs from that of the Distichodus type jaw in two ways. Firstly, the anteriorprocess of the angulo-articular in the Ichthyborus and Mesoborus jaw forms is directed horizontallyforward rather than having the dorsal or anterodorsal orientation that characterizes the Dis-tichodus type jaw. Furthermore, rather than simply abutting the medial surface of the dentarythe angulo-articular in these taxa inserts into a depression (Ichthyborus) or fossa (Mesoborustype) on the posteromedial surface of the dentary. These modifications and other adaptationspermit an apomorphic greatly increased mobility between the dentary and angulo-articular. The Ichthyborus type articulation (Fig. 3c) is specific to that genus and characterized by anelongate angulo-articular considerably thickened posterior to the rear margin of the dentary.This expanded posterior portion of the angulo-articular is undercut anteriorly to form a deepnotch into which the posteroventral corner of the dentary fits. Both the thickening of the posteriorportion of the angulo-articular and its relationship to the dentary are apomorphic charactersseemingly unique to this genus among characoids. The Mesoborus form of articulation betweenthe angulo-articular and dentary is common, with some variation, to Mesoborus, Microstomatich-thyoborus, Eugnatichthys, Paraphago, Phago and Belonophago. In these genera the anteriorportion of the angulo-articular inserts into a definite socket on the medial surface of the dentary.Along with the pronounced overlap of the dentary and angulo-articular, this adaptation shiftsthe pivot point of the dentary anteromedially. Within the assemblage characterized by theMesoborus type articulation several subunits are distinguished by further modifications of theangulo-articular. In contrast to its plesiomorphously elongate state, the angulo-articular inEugnatichthys, Paraphago, Phago and Belonophago is a thickened element that is both shortenedhorizontally and shifted practically entirely onto the medial surface of the dentary (Fig. 3d).As a consequence the rear of the dentary extends nearly to the vertical through the joint of theangulo-articular with the quadrate. This apomorphic shortening of the angulo-articular isespecially notable in Eugnatichthys in which the greatly thickened bone is barely visible laterally. Keeping in mind the difficulties in determining the mode of action of a complex system on thebasis of preserved material, it nonetheless appears that the two lower jaw pivot points (dentary-angulo-articular and angulo-articular-quadrate) in the Ichthyborus and Mesoborus jaw forms resultin systems that are functionally unique among characoids. In Ichthyborus the ventral border ofthe dentary makes an oblique angle with that of the angulo-articular when the mouth is closed.As the mouth opens, the pivoting of the premaxilla on the supraethmoid causes the rear of thepremaxilla to move ventrally. This motion is imparted via the reduced maxilla to the rear of thedentary. The entire lower jaw in turn shifts ventrally, with the dentary pivoting on the angulo-articular simultaneous with the pivoting of the entire dentary-angulo-articular complex on the CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 271 quadrate. Both motions continue until the ventral borders of the angulo-articular and dentaryachieve their plesiomorphous straight line orientation. During the second phase of jaw motionthe mobility of the dentary relative to the angulo-articular ceases and these elements act as a rigidunit pivoting on the quadrate. Thus during the opening of the mouth, two functional phases arediscernible; an apomorphic first phase characterized by mobility at both pivot points, and asecond phase demonstrating only the plesiomorphous motion of the angulo-articular on thequadrate. Such a two-phase system is common to Ichthyborus, Mesoborus and Microstomatich-thyoborus, and is the basis for the more derived jaw motion of Eugnatichthys, Paraphago, Phagoand Belonophago which have continual mobility between the angulo-articular and dentarythroughout the entire cycle of jaw action. In these latter genera the ventral borders of the angulo-articular and dentary pass from the oblique concave angle of the closed jaw, to a straight-lineorientation and then to a distinct convex relationship in the fully open mouth (see Gregory &Conrad, 1938, Fig. 35). This last apomorphic phase of the motion is, as far as can be determined,unique to these four genera among characoids. Upper jaw The plesiomorphous condition of the upper jaw in characoids appears to have the premaxillaimmovably attached by tight syndesmotic articulations to the supraethmoid and lateralsupraethmoid wings. Such attachment occurs either along the medial surface of the premaxilla(e.g. Hepsetus, Acestrorhynchus) or more usually to a posteriorly-directed ascending process ofthe premaxilla (e.g. Brycon, Alestes). Medially the premaxillae are completely or nearly completelyseparated symphyseally by an elongate supraethmoid spine. Plesiomorphously the maxilla is amoderately to markedly elongate element movably articulated with the posterodorsal edge of thepremaxilla, and bearing anterodorsally a medially-directed process which attaches ligamentouslyto the palatine and ligamentum primordiale. Citharinids and distichodontids differ from thisplesiomorphous upper jaw plan both in the relationships of the premaxilla with its partner and thesupraethmoid, and in the form of the maxilla and its relationship to the premaxilla and dentary. All citharinids and distichodontids lack the prominent premaxillary ascending process andtight connective tissue bands which plesiomorphously attach the premaxilla immovably to thesupraethmoid. Instead a series of modifications of the premaxilla and supraethmoid result in amobile articulation of the upper jaw with the supraethmoid. The various adaptations of thesupraethmoid will be discussed in detail later in the paper. For the purposes of the discussion atthis point, it suffices to note that among citharinids and distichodontids the plesiomorphousstate of the forward edge of the supraethmoid is hypothesized to be an anteriorly trifurcatecomplex. In this condition a median plate extends anteriorly over the premaxillary symphysis,and ventrolateral articular processes insert into articular fossae on the rear of the premaxillae.In Xenocharax the articular fossa of the premaxilla has the form of a deep horizontal depressionopen to its partner across the symphysis and extending from the symphysis midway across thetransverse width of the premaxilla. Such a horizontal fossa is hypothesized to be plesiomorphousfor citharinids and distichodontids in so far as the corresponding horizontal supraethmoidprocess represents the least pronounced alteration of the primitively horizontal edge of thesupraethmoid. Within citharinids and distichodontids, several derived modifications of this formof premaxillary fossa are found. Among citharinids there occurs a progressive ontogenetic reduction of the roof of the basicallyXenocharax form of articular fossa that characterizes juveniles of Citharinus and Citharidium.As a consequence in adult citharinids the fossa roof is reduced to a small shelf at the lateralmargin of the depression. Thus the primitively ventral surface of the fossa is now exposed dorsallyand is ligamentously attached to the median process of the supraethmoid. Such an attachmentcontrast with the latter's plesiomorphous attachment to the dorsal surface of the roof of thefossa. Within the complex formed by Distichodus, Hemigrammocharax and Nannocharax there occursa phylogenetic transition in the form, position and extent of development of the premaxillaryfossa. Distichodus notospilus and D. brevipinnis have a basically Xenocharax form of widehorizontal fossa on the posterior surface of the premaxilla. In comparison in Distichodus lusosso, 272 R. P. VARI D. niloticus and D. fasciolatus the fossa is a conical pit located on the posterodorsal surface ofthe premaxilla. These adaptations are correlated with the posteroventral shift of the premaxillaein these species, a repositioning carried further in Nannocharax and Hemigrammocharax. In theselatter genera the premaxillae are located distinctly ventral to the supraethmoid and the articularfossae are reduced either to small conical depressions on the dorsal surface of the premaxillaeor are entirely lacking. An evidently independent shift of the fossa to the dorsal surface of thepremaxilla occurs in Hemistichodus in which the articular fossa is a rounded groove on theposterodorsal surface of the premaxilla. Finally, in Eugnatichthys, Paraphago, Phago andBelonophago the articular fossa is a transversely directed pit on the medial surface of thelongitudinally-oriented posterior portion of the premaxilla. This adaptation is especially pro-nounced in the last two genera. The above modifications, those of the supraethmoid and a series of other alterations permitvarying degrees of mobility of the premaxilla on the supraethmoid. Such motion is limited incitharinids but more pronounced in distichodontids, especially in Distichodus, Nannocharax,Hemigrammocharax, Hemistichodus, Ichthyborus, Microstomatichthyoborus, Mesoborus,Eugnatichthys, Paraphago, Phago and Belonophago. The upper jaw motion of these genera takestwo forms. In Distichodus, Nannocharax and Hemigrammocharax the posteroventrally shiftedpremaxillae are notably mobile in the horizontal plane. In contrast, in the other distichodontidslisted, the jaw modifications permit a pronounced pivoting of the premaxillae on the supraethmoidwith a consequent increase in the vertical extent of the gape. Among characoids other than citharinids and distichodontids, mobile premaxillary-supraeth-moid articulations occur in the African characid genus Hydrocynus, and the Neotropical characoidfamilies Anostomidae, Chilodontidae, Prochilodontidae, Parodontidae and Hemiodontidae(Roberts, 1974). Argonectes and Bivibranchia, in turn, have radically altered protrusible upperjaws in which the premaxilla separates from the supraethmoid during opening of the mouth.Comparison of the mobile upper jaw in Hydrocynus with that of citharinids and distichodontidsreveals pronounced anatomical and functional differences between these systems. The consequentlikelihood that these complexes represent independent acquisitions of upper jaw mobility issupported by the series of derived characters uniting Hydrocynus to African characids havingimmovable premaxillary-supraethmoid articulations (see Comments on the African Characidae).Argonectes, Bivibranchia and the family Hemiodontidae differ from citharinids and distichodontidsboth in their mode of premaxillary mobility and in their possession of a rhinosphenoid. Therhinosphenoid is a median orbital ossification unique to various South American characoidgroups, most of which are characterized by a plesiomorphous immobile upper jaw. On the basisof the common possession of a rhinosphenoid and other characters, it is most parsimonious toassume that hemiodontids, Bivibranchia and Argonectes are closely related to Neotropicalrhinosphenoid-bearing characoids with immovable upper jaws. In light of this, and the differencesin the type of supraethmoid-premaxillary articulation, it appears that upper jaw mobility in thesegroups has been achieved independent of that in citharinids and distichodontids. Finally, pro-chilodontids, anostomids and the closely related chilodontids achieve upper jaw mobility bymotion of the ascending arm (Anostomidae, Chilodontidae) or body (Prochilodontidae) of thepremaxilla along the edge of the supraethmoid spine rather than via the citharinid and dis-tichodontid type of hinging of the premaxilla on anterior processes of the supraethmoid. Assuch, the premaxillary mobility of these South American families appears to be non-homologouswith that of citharinids and distichodontids. The closest approximation among charcoids to thecitharinid and distichodontid type of premaxillary-supraethmoid articulation is found in theNeotropical family Parodontidae. The members of this family have a distinct dorsomedial pre-maxillary fossa articulating with anterolateral processes of the supraethmoid. However, asdiscussed in the Conclusions section, the parodontid fossa appears to be convergent with that ofcitharinids and distichodontids rather than an indicator of close relationship between the groups. As was the case with the dentary symphysis, the interpremaxillary articulation among citharinidsand distichodontids demonstrates several apomorphous modifications of varying levels ofuniversality. Contrary to the plesiomorphous, limited syndesmotic contact of the premaxillaeanterior to the supraethmoid spine citharinids and distichodontids have the medial surfaces of CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 273 the premaxillae broadly in contact. Within these families, however, the exact form and extent ofthe contact varies significantly. In Xenocharax, Nannaethiops and Neolebias the combination of asyndesmotic joint and a somewhat narrow premaxillary symphysis permits a limited mobilitybetween the premaxillae. Although retaining the plesiomorphous syndesmotic joint, Paro-dist ichodus, Distichodus, Nannocharax, Hemigrammocharax and Hemistichodus are immovablyjoined symphyseally. This immobility is a consequence of the expanded cross-sectional extent ofthe jaws around the widened replacement tooth trenches. Finally, Ichthyborus, Microstomatich-thyoborus, Mesoborus, Eugnatichthys, Paraphago, Phago and Belonophago have a series ofinterdigitating convolutions at the rear of the premaxillary symphysis. This synarthritic jointeliminates all motion between the premaxillae, a trend that is carried further in Ichthyborus monodiin which the premaxillae are fused symphyseally. This fusion is, as far as can be determined,unique to this species among characoids and perhaps a function of its markedly elongate jaws. pmx mx Fig. 4 Ichthyborus quadrilineatus, upper jaw, left lateral view. A second form of synarthritic interpremaxillary joint characterizes the family Citharinidae. InCitharinm and Citharidium the longitudinal extent of the premaxillary symphysis is increasedby the expansion of the median portions of the premaxillae posteriorly to form a prominentsymphyseal bulge. This posterior expansion of the premaxillae along with a series of highlydeveloped symphyseal interdigitations tightly join the premaxillae synarthrically. These pre-maxillary sutures differ, however, from those of some distichodontids both in the form andextent of the interdigitations, and in their association with the posteriorly expanded portion ofthe premaxilla. The consequent likelihood that the premaxillary sutures in the two groups arenon-homologous is supported by the overall distribution of derived characters in these families. Although the possession of interpremaxillary sutures is considered an apomorphous characteron the basis of outgroup comparisons, such adaptations are not unique to citharinids and dis-tichodontids within the Characoidea. Such sutures have been previously reported for theNeotropical genus Brycon (Weitzman, 1962) and the old world characid Hydrocynus (Eastman,1917). Interpremaxillary sutures have also been found during this study in the South Americancharacid genera Triportheus and Serrasalmus, and the African characids Bryconaethiops andAlestes. However, on the basis of a series of derived characters (the possession of a rhinosphenoid,tooth form and distribution, etc.) the South American genera appear to be most closely relatedto Neotropical characoids lacking interdigitating premaxillary sutures. Similarly, the old worldgroups form a monophyletic unit with African genera lacking the synarthritic joint (see p. 341).Consequently, the interpremaxillary suturing in these South American and African characoidsappears to have been acquired independently of that in citharinids and distichodontids. The final jaw character of interest is the form of the maxilla and its relationship to the pre-maxilla and dentary. The hypothetical plesiomorphous state of the maxilla among characoids isa relatively large, tooth-bearing element movably attached to the premaxilla, and with a dorso-medially directed process for the attachment of the palatine and ligamentum primordiale. InCitharinus and Citharidium, in contrast, the maxilla is relatively reduced but retains its mobility, 274 R. P. VARI flattened plate-like form and dorsomedially directed process. The maxilla in the distichodontidgenera Hemistichodus, Ichthyborus, Microstomatichthyoborus, Mesoborus, Eugnatichthys,Paraphago, Phago and Belonophago is also reduced. However, in these genera the relativereduction of the bone is much more pronounced than in citharinids. Furthermore, the maxillain these genera is unique among characoids examined in its lack of a dorsomedial process and inbeing immovably joined, but not fused, to the rear of the enlarged premaxilla (Fig. 4). Thesemaxillary alterations are most pronounced in Hemistichodus in which the bone is greatly reducedboth relative to the generalized characoid condition and also with respect to that in the othergenera listed. Furthermore, the maxilla in Hemistichodus is autapomorphically shifted onto thedorsal surface of the premaxilla (see Daget, 1968, Fig. 2) and is consequently totally removed fromthe ventral border of the upper jaw. Finally, the assemblage consisting of Eugnatichthys, Para-phago, Phago and Belonophago is characterized by a recontouring and expansion of the postero-ventral portion of the reduced maxillary into a rounded somewhat bulbous process. Duringmovements of the jaws this portion of the maxilla closely articulates with and slides along thepreviously described groove on the lateral surface of the posterodorsal dentary ramus.In summary, the diverse apomorphic jaw modifications described above are : 1 the outward rotation of the replacement tooth trench in citharinids, and the greatexpansion of the trenches in distichodontids other than Xenocharax, Nannaethiops andNeolebias. 2 the lack of an interdigitating symphyseal hinge joint in citharinids and distichodontids. 3 the fused dentaries of Ichthyborus. 4 the bony interdigitations along the posterior portion of the dentary symphysis inMicrostomatichthyoborus, Mesoborus, Eugnatichthys, Paraphago, Phago andBelonophago. 5 the posteriorly directed process lateral to the dentary symphysis in Nannocharax andHemigrammocharax. 6 the pronounced posterodorsal dentary ramus in Hemistichodus, Ichthyborus, Micro-stomatichthyoborus, Mesoborus, Eugnatichthys, Paraphago, Phago and Belonophago.This process is laterally modified to form a groove articulating with the maxilla in thelast four genera and is greatly developed autapomorphically in Hemistichodus. 1 the mobile joint between the dentary and angulo-articular in all distichodontids otherthan Xenocharax, Neolebias, Nannaethiops and Paradistichodus. The four forms of thismobile articulation are : (A) the Hemistichodus type limited to that genus and plesiomorphous with respectto the Ichthyborus, Mesoborus and Distichodus forms of the joint. (B) the Distichodus type occurring in Distichodus, Nannocharax and Hemigrammo-charax. (C) the Ichthyborus type limited to that genus. (D) the Mesoborus type common to Microstomatichthyoborus, Mesoborus,Eugnatichthys, Paraphago, Phago and Belonophago. The last four genera share anapomorphic further reduction of the horizontal extent of the angulo-articular. 8 the premaxillary articular fossa in citharinids and distichodontids. 9 the ontogenetic reduction of the premaxillary fossa roof in citharinids. 10 the reduction in the extent, and the shift of the articular fossa to the dorsal surface ofthe premaxilla in Nannocharax, Hemigrammocharax and some Distichodus species. 1 1 the rounded articular fossa on the dorsal surface of the premaxilla in Hemistichodus. 12 the laterally-directed articular fossa in Eugnatichthys, Paraphago, Phago and Belono-phago. 13 the reduced maxilla of citharinids. 14 the greatly reduced, immobile maxilla in Hemistichodus, Ichthyborus, Microstomatich-thyoborus, Mesoborus, Eugnatichthys, Paraphago, Phago and Belonophago. 15 the bulbous, posteroventrally expanded maxilla in Eugnatichthys, Paraphago, Phagoand Belonophago. CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 275 16 the position of the maxilla on the dorsal surface of the premaxilla in Hemistichodus. 17 the interdigitating premaxillary symphyseal processes in citharinids and some dis-tichodontids. Dentition Characoids are notable for, and largely classified on, the basis of their broad range in tooth formand arrangement. Such variation is evident in the morphology, distribution and mode ofimplantation of the dentition in the Citharinidae and Distichodontidae. Roberts (1967, p. 231)hypothesized that 'the most primitive dentition in characoids consists of conical teeth on thepremaxillary, a single row of conical teeth extending beyond the gap of the maxillary, and tworows of conical teeth in the lower jaw separated by a shallow replacement trench'. Such a dentalplan is consistent with our present knowledge of characoid ontogeny and phylogeny and would,with the exception of the tooth form, appear to have been the condition in the common ancestorof citharinids and distichodontids. A bicuspidate equally-cusped tooth (Fig. 2) is common to all citharinids and distichodontids atsome point in ontogeny. Multicuspidate dentition, either in the form of linearly arranged cusps(e.g. cheirodontines) or an arched cusp series along the edge of a wide tooth (e.g. Brycon, Alestes),is widespread among characoids. However, the bicuspidate tooth form of citharinids and dis-tichodontids appears to be unique to, and apomorphic for, these families among characoids. Within the Distichodontidae two assemblages have sequential ontogenetic replacement of theequally-cusped dentition by teeth demonstrating a relative enlargement of one cusp. In Ichthyborusthis takes the form of a markedly developed anterior cusp, while Microstomatichthyoborus,Mesoborus, Eugnatichthys, Paraphago, Phago and Belonophago have the posterior cusp enlarged.The shift from the equally-cusped tooth form, plesiomorphous for distichodontids, to theunequally-cusped condition can be followed ontogenetically in representative species demon-strating each form of enlarged cusp. Among species with an enlarged anterior cusp, an ontogenetic series of Ichthyborus bessereveals a progressive shift to teeth with a relatively larger anterior cusp (Fig. 5a). In 30 mm SLspecimens, the anterior cusp of the teeth at the front of each jaw is somewhat enlarged relative tothe posterior cusp. This relative difference in cusp size decreases posteriorly so that the teethat the rear of each jaw have equally-sized cusps. By 70 mm SL the anterior cusps of all teeth arelarger than the posterior, with this difference again most pronounced anteriorly. Appreciablyenlarged anterior cusps occur on all teeth in 100 mm SL specimens with the posterior cusp of theanterior teeth very small. Ichthyborus besse specimens of 150 mm SL have the posterior cusp onmost teeth so reduced relative to the anterior cusp as to give the teeth a unicuspidate appearance.A similar, though not as pronounced, ontogenetic transition in tooth-cusp size occurs in Ichthy-borus ornatus and /. quadrilineatus over the limited size range of specimens examined. It was notpossible, however, to confirm the predicted ontogenetic transition in tooth form for /. monodiwhich is only known from adult specimens. A size range of Mesoborus crocodilus, a species with an enlarged posterior tooth cusp, showsa progressive ontogenetic increase in the size of the posterior cusp (Fig. 5b). In 45 mm SLspecimens the anterior teeth, particularly of the upper jaw, show a distinct enlargement of theposterior tooth cusp, with the remaining teeth retaining the plesiomorphous equally-cuspedcondition. By 55 mm SL nearly all the teeth in the upper jaw and those in the anterior half ofthe lower jaw exhibit an enlarged posterior cusp to varying degrees. At 70 mm SL the anteriorcusp is totally lacking on the anterior teeth and greatly reduced on the remaining teeth of bothjaws. The dentition of Mesoborus specimens of greater than 120 mm SL is nearly unicuspidatewith a rudimentary anterior cusp remaining only on the posterior teeth of each jaw. It should beemphasized, however, that the relative difference in tooth cusp size found in Mesoborus is notuniversal among genera having an enlarged posterior tooth cusp. In Microstomatichthyoborusthe posterior tooth cusp is only slightly enlarged. A slightly greater relative development of thecusp occurs in Belonophago (see Poll, 1957, Fig. 141), while Eugnatichthys, Paraphago and Phagoshow a marked enlargement of the posterior cusp, although the difference is not as appreciableas that of Mesoborus. 276 R. P. VARI The mode of implantation of the outer tooth row also varies within the complex formed bycitharinids and distichodontids. In all citharinids and the distichodontid genera Xenocharax,Nannaethiops and Neolebias the teeth attach by flattened or slightly oblique bases to a series ofsockets along the distal edge of the replacement tooth trench ridges (Fig. la). Such an acrodonttype of tooth attachment is generalized, though not universal, for characoids and tooth-bearingostariophysans and is thus hypothesized to be plesiomorphous for citharinids and distichodontids. A B Fig. 5 Ontogenetic variation in dentition of A. Ichthyborus besse (fifth premaxillary tooth at 32, 50and 115 mm SL), B. Mesoborus crocodilus (fourth premaxillary tooth at 55, 85 and 130 mm SL),left lateral view. The outer row of dentition in all remaining distichodontid genera, in comparison, has the toothform and mode of attachment illustrated in Figs Ib and c. In this condition, the teeth of theouter tooth row taper gradually to fit the anterior contours of the replacement tooth trench towhich they have a ligamentous (pleurodont) attachment. As a consequence, the total relative lengthof the teeth is increased, with this elongation most pronounced in Distichodus, Nannocharaxand Hemigrammocharax. The genera Hemistichodus, Ichthyborus, Microstomatichthyoborus,Mesoborus, Eugnatichthys, Paraphago, Phago and Belonophago, in turn, are characterizedby relatively stronger teeth than those of citharinids and other distichodontids. Although theforward extension of the posterior wall of the replacement tooth trench results in what appear tobe a series of interconnected sockets for the enlarged outer tooth row, in actuality these teethretain their pleurodont attachment to the anterior wall of the trench (Fig. Ic). The distribution pattern of the dentition within citharinids and distichodontids shows bothreductions and increases relative to the previously described hypothetical plesiomorphous con-dition for characoids (see p. 275). The plesiomorphously present inner dentary tooth row is lackingin citharinids, Nannocharax, Hemigrammocharax, Hemistichodus and all Ichthyborus speciesother than /. besse. On the basis of the hypothesized phylogeny (see p. 338) this absence of theinner row of dentary teeth appears, however, to have arisen via multiple independent losses. Theopposite trend of an increase in the number of inner tooth rows on the dentary occurs inXenocharax and some Neolebias trilineatus specimens (Daget, 1965, p. 7) which have two innertooth rows, and in Ichthyborus besse where the inner row of dentary dentition is expanded into abroad band. In the upper jaw, the dentition of both the premaxilla and maxilla varies within the assemblageformed by the Citharinidae and Distichodontidae. Contrary to the hypothesized plesiomorphousstate of a tooth-bearing maxilla, citharinids and all distichodontids with the exception ofXenocharax, Nannaethiops and Neolebias have edentulous maxillae (the reported absence ofmaxillary teeth in some Neolebias species is erroneous, see p. 330). An inner premaxillary toothrow occurs in all distichodontids other than Nannocharax, Hemigrammocharax, Hemistichodus,Ichthyborus ornatus and /. monodi, all of which also lack the inner dentary tooth row. The lackof the inner row of premaxillary dentition in these taxa and in citharinids would appear to beapomorphous though considered to represent several independent losses on the basis of thehypothesized phylogeny. Ichthyborus besse, in contrast, has the inner row of premaxillary dentition CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 277 expanded into a broad tooth patch. Finally, Hemistichodus is distinguished by the autapo-morphous lack of the medial premaxillary teeth (see Poll, 1957, Fig. 134). The final tooth character of phylogenetic interest among citharinids and distichodontidsinvolves the canine dentition in Ichthyborus and Mesoborus. Ichthyborus has an enlarged unpairedtooth in the midline of the fused dentaries, an adaptation unique to this genus among characoidsexamined. The median dentary tooth and that flanking it on each side interdigitate with a pairof enlarged teeth at the anterior of the premaxillae (see Poll, 1957, Figs 132 & 136). In Ichthyborusquadrilineatus these dentary and premaxillary teeth are only slightly enlarged, with a limited over-lap between the anterior teeth of the upper and lower jaws. However, in /. ornatus, I. besse and/. monodi these teeth are produced into prominent, significantly overlapping canines. A different form of caniniform dentition characterizes Mesoborus. Although sharing withIchthyborus an enlargement of the anterior premaxillary teeth, the dentary dentition in thisgenus is markedly different. Mesoborus lacks the unpaired median dentary tooth and the enlargedteeth flanking it that occur in Ichthyborus. Instead, the anteriormost dentary teeth of Mesoborusare quite small and the second to fourth teeth are strongly developed. These enlarged teetharise from a distinct convex portion of the dorsal edge of the dentary and fit lateral to a series ofrelatively small teeth on a corresponding concave region of the premaxilla (see Gregory &Conrad, 1938, Fig. 34). Such a pattern of dentary and premaxillary dentition is not encounteredelsewhere in the families under study, and is hypothesized to be derived relative to the gradeddentition of most characoids. In summary, the derived states of the dentition among citharinids and distichodontids arehypothesized to be: 1 the common possession in these families of a bicuspidate tooth. This tooth form issecondarily apomorphically modified by an enlargement of the anterior cusp in Ichthy-borus, and of the posterior cusp in Microstomatichthyoborus, Mesoborus, Eugnatichthys,Paraphago, Phago and Belonophago. 2 the pleurodont tooth attachment in all distichodontids other than Xenocharax, Nan-naethiops and Neolebias. 3 the loss of maxillary teeth in citharinids and all distichodontids other than Xenocharax,Nannaethiops and Neolebias. 4 the loss of the inner dentary tooth row in Nannocharax, Hemigrammocharax, Hemisti-chodus and all Ichthyborus species other than /. besse. 5 the loss of the inner dentary tooth row in citharinids, Nannocharax, Hemigrammocharax,Hemistichodus, Ichthyborus ornatus and /. monodi. 6 the lack of the medial premaxillary teeth in Hemistichodus.1 the enlarged median dentary tooth of Ichthyborus. 8 the form of caniniform dentition in Mesoborus. Supraethmoid The supraethmoid form hypothesized plesiomorphous for characoids is an anteriorly triangularbone extending between, and completely or nearly completely separating, the premaxillae. Thesupraethmoid usually bears along its lateral margin a somewhat triangular process, the lateralsupraethmoid wing, which is, however, lacking in many characoids with an elongate skull. Asdiscussed previously, the supraethmoid of citharinids and distichodontids is greatly modifiedanteriorly as part of a system permitting upper jaw mobility. The least derived condition of thesupraethmoid in these families occurs in Xenocharax in which the bone is relatively short longi-tudinally and lacks the plesiomorphously present lateral supraethmoid wings. More significantfrom a functional viewpoint are the marked modifications of its anterior edge. In contrast to thesimple supraethmoid spine of the hypothesized plesiomorphous characoid state, in Xenocharaxthe supraethmoid is elaborated anteriorly into a wide trifurcate complex (Fig. 6a). Medially ashort horizontal shelf extends forward from the anterodorsal edge of the supraethmoid to overlieand attach ligamentously to the dorsomedial portion of the premaxillae. On either side of, andslightly ventral to, this median process there is an anteriorly directed horizontal articular process 278 R. P. VARI which partially inserts into, and ligamentously attaches to, the previously described premaxillaryfossa. As discussed earlier, the Xenocharax condition of a wide horizontal articular process isconsidered plesiomorphous for citharinids and distichodontids in that it represents the leastderived modification of the primitively horizontal edge of the supraethmoid. Although the exacihomology, if any, of the three supraethmoid processes with the primitively present supraethmoidalspine and lateral wings is unknown, these modifications of the anterior region of the supraethmoidappear to be apomorphous within characoids and as such are indicative of the monophyleticnature of the unit formed by the Citharinidae and Distichodontidae. The somewhat similararticular processes present in the South American characoid family Parodontidae differ in overallform and are considered to be independently acquired (see p. 349). Fig. 6 Supraethmoid of A. Xenocharax spilurus, B. adult Citharinus citharus, C. Distichodus niloticus, D. Phago loricatus, dorsal view. Various modifications of the Xenocharax form of supraethmoid distinguish the Citharinidaeand subunits of the Distichodontidae. Juvenile citharinids have a basically Xenocharax type ofsupraethmoid with the anteromedial supraethmoid process overlying the premaxillae andprominent articular processes inserting into the premaxillary fossae. Congruent with the pre-viously described ontogenetic alterations of the premaxillary fossae, citharinids demonstrate anontogenetic increase in the extent of median supraethmoid process and a reduction of the lateralarticular processes. The broad articular processes that are present in juvenile citharinids areprogressively reduced along their lateral margins until the remaining medial portions coalescewith the enlarged median process. These alterations result in a single enlarged median supraeth-moid process (Fig. 6b), in contradistinction to the juvenile anteriorly trifurcate supraethmoid.As a consequence of this restructuring of the supraethmoid and the correlated changes of thepremaxillary articular fossa, in adult citharinids the enlarged median process of the supraethmoidoverhangs and directly contacts the ventral surface of the articular fossa. Such an associationcontrasts with the plesiomorphous, and ontogenetically earlier, attachment of the mediansupraethmoid process to the dorsal surface of the fossa roof. In addition to the above adaptationsof the anterior edge of the supraethmoid, Citharinus and Citharidium have the cranial fontanelleextending midway along the longitudinal extent of the bone. Such a forward extension of thefontanelle is lacking among distichodontids and rare among characoids in general. As such it isconsidered apomorphous for citharinids among characoids. CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 279 Several subunits of the Distichodontidae demonstrate distinctive modifications to the articularprocesses of the supraethmoid, and of overall supraethmoid form. In Distichodus, Nannocharaxand Hemigrammocharax the median supraethmoid process is greatly reduced relative to the lateralarticular processes. The latter, in turn, show a transition in form and orientation within thesegenera. The articular processes of Distichodus notospilus and D. brevipinnis retain the plesio-morphous flattened, horizontal form, although being somewhat more medially directed than inXenocharax. The other Distichodus species examined, along with the genera Hemigrammocharaxand Nannocharax, have the lateral articular processes modified into pointed, anteroventrally-directed prongs (Fig. 6c). In these taxa the articular processes either insert into a conical fossa onthe posterodorsal face of the premaxilla (Distichodus) or attach ligamentously to the dorsalsurface of that element (Hemigrammocharax and Nannocharax). Congruent with these alterationsof the articular processes are changes in the overall form of the supraethmoid. Whereas thesupraethmoid in D. notospilus and D. brevipinnis is relatively square, as it is in Xenocharax, thoseDistichodus species with prong-like articular processes have narrow elongate supraethmoids(Fig. 6c). This supraethmoid elongation and that of the articular processes appear to be correlatedwith the posteroventral shift of the premaxilla relative to the supraethmoid in these taxa. Thedistichodontid genus Paradistichodus also has a long, slender supraethmoid which in overallproportions resembles that of Hemigrammocharax and Nannocharax. However, contrary to thestate of the supraethmoid in those genera. Paradistichodus retains the plesiomorphous conditionof wide horizontal articular processes and a relatively large median process. Two other supraethmoid modifications of note occur among distichodontids. In Hemistichodusthe supraethmoid is greatly reduced to a small element totally lacking the median supraethmoidprocess, and with the articular processes rounded and laterally directed (see Daget, 1968, Fig. 3).Similarly, but evidently independently, the median supraethmoid process is reduced to approxi-mately one-half of its plesiomorphous size in Microstomatichthyoborus and Mesoborus, andfurther diminished to a small pointed element in Eugnatichthys, Paraphago, Phago and Belono-phago. Congruent with this reduction of the median supraethmoid process is an enlargement andreorientation of the articular processes in these genera. In Microstomatichthyoborus and Mesoborusthese processes retain the plesiomorphous form of anteriorly-directed, horizontal plates.Eugnatichthys and Paraphago, in contrast, have less flattened articular processes that are both rela-tively larger and more distinctly orientated. Finally, in Phago and Belonophago the articularprocesses are markedly enlarged, bulbous, laterally-oriented structures (Fig. 6d). The apomorphous modifications of the supraethmoid among citharinids and distichodontidsare summarized as follows : 1 the anteriorly trifurcate form of the supraethmoid or a further derived state of thestructure that is common to citharinids and distichodontids. 2 the reduction of the articular processes of the supraethmoid and their fusion with theenlarged median supraethmoid process in citharinids. 3 the reduction of the median supraethmoid process and restructuring of the lateral articularprocesses into pointed, anteroventrally-directed prongs in Hemigrammocharax, Nan-nocharax and some Distichodus species. Congruent with these changes, these taxademonstrate a pronounced elongation of the supraethmoid. 4 the elongation of the supraethmoid in Paradistichodus. 5 the greatly reduced supraethmoid in Hemistichodus. 6 the progressive reduction of the median supraethmoid process, and the enlargement andlateral reorientation of the articular processes in Microstomatichthyoborus, Mesoborus,Eugnatichthys, Paraphago, Phago and Belonophago. Anterior orbital region The plesiomorphous condition of the anterior orbital region for characoids is hypothesized tohave the orbitosphenoid separated from the lateral ethmoid. In this condition the olfactorynerve exits either from the anteromedian opening of the orbitosphenoid or through a foramenalong its anterior face. The nerve then extends obliquely across the anteromedial region of the 280 R. P. VARI orbital cavity to the olfactory foramen of the lateral ethmoid. In contrast, citharinids and disticho-dontids, together with various South American and African characoid groups, have a directcontact of the lateral ethmoid and orbitosphenoid, with the olfactory bulb and tract coveredlaterally. In the following discussion the forms of this contact in the Citharinidae and Disticho-dontidae are first described and then contrasted to those in characoid outgroups. 2mm paraFig. 7 Xenocharax spilurus, anterior orbital region, left lateral view. Distichodontids other than Nannaethiops and Neolebias are characterized by the type of lateralethmoid-orbitosphenoid contact illustrated in Fig. 7 or a further derived state of such anarticulation. In the simplest condition, such as that of Xenocharax, the lateral ethmoid bears aprominent horizontal or posterodorsally sloping process which extends posteriorly from thepostermedial portion of the lateral ethmoid to contact the anterolateral edge of the orbito-sphenoid. This lateral ethmoid process forms a strut that laterally overlaps the olfactory bulb andtract and extends between the superior and inferior oblique muscles. As a consequence theentrance into the anterior myodome is horizontally divided posteriorly. les Fig. 8 Nannocharax elongatus, anterior orbital region, left lateral view. The distichodontid genera Hemigrammocharax and Nannocharax share a further derived formof this type of contact between the lateral ethmoid and orbitosphenoid (Fig. 8). In these generathe posterior process of the lateral ethmoid undergoes a progressive vertical expansion phylo-genetically, with a consequent increase in the vertical extent of the articulation between the CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 281 lateral ethmoid and orbitosphenoid. Although the posterior process of the lateral ethmoid inHemigrammocharax monodi and Nannocharax multifasciatus is vertically deeper than that oc-curring in Xenocharax, it is nonetheless distinctly separated dorsally from the ventral surface ofthe frontal. Thus these species retain a large opening dorsally for the passage of the superioroblique muscle into the anterior myodome. In Nannocharax gobioides, N. fasciatus and TV.intermedius, however, the posterior process of the lateral ethmoid is greatly expanded vertically.This expansion both increases the vertical contact between the posterior process of the lateralethmoid and the orbitosphenoid and further reduces the dorsal aperture into the anteriormyodome. 2mm paraFig. 9 Citharinus citharus, adult, anterior orbital region, left posterolateral view. In contradistinction to the condition in all other distichodontids, the genera Nannaethiops andNeolebias lack any direct contact between the lateral ethmoid and orbitosphenoid. This absenceof the lateral ethmoid strut is, however, hypothesized to be a secondary loss rather than a primarylack of such a structure. Such an hypothesis is congruent with the most parsimonious recon-struction of relationships among distichodontids, and with the myriad reductional trendsdemonstrated by the monophyletic unit formed by Nannaethiops and Neolebias. Furthermore, inNannaethiops unitaeniatus, in which the reductional trends characteristic of these genera are leastpronounced, there occurs a short posteriorly-directed lateral ethmoid process lateral to theolfactory foramen. This process may very well represent a reduced form of the Xenocharaxstrut. The form of lateral ethmoid-orbitosphenoid contact common to all citharinids differs entirelyfrom that in distichodontids. In Citharinus and Citharidium the orbitosphenoid is shifted to theanteroventral edge of the pterosphenoid as a consequence of the deep orbital lamella of thefrontal characteristic of citharinids. The orbitosphenoid of citharinids extends ventrally, as anearly vertical pillar, to contact the parasphenoid dorsally, and then continues forward as alarge, anteriorly-directed, anterolaterally diverging process which articulates with a posterolateralprocess of the lateral ethmoid (Fig. 9). Juveniles of Citharinus and Citharidium possess solelythis ventral bony contact of the lateral ethmoid and orbitosphenoid. In the anterodorsal regionof the orbit, juvenile citharinids have a large cartilage block in the area between the anterioredge of the orbital lamella of the frontal and the posteromedial portion of the lateral ethmoid.This cartilage mass undergoes a progressive ontogenetic ossification from the anterodorsal portionof the orbitosphenoid. As a consequence in all larger citharinid specimens examined (Citharinuslatus, C. citharus, C. congicus, C. distichoides and C. gibbosus] the area occupied earlier inontogeny by the cartilagenous block is filled by a prominent process of the orbitosphenoid. This 282 R. P. VARI ossification extends anterior of the orbital lamella of the frontal along the ventral surface of thatbone to either coalesce or synchondrally join with a smaller posterodorsal process of the lateralethmoid. Although large specimens of all citharinid species were not available for examination,it appears that such an anterodorsal orbitosphenoid process probably occurs in the adults ofCitharidium and other Citharinus species. These dorsal processes of the lateral ethmoid andorbitosphenoid, along with the aforementioned ventral articulation of these bones, restrict theentrance to the anterior myodome in citharinids to a single horizontally elongate fenestra. Neither the dorsal nor the ventral articulation between the orbitosphenoid and lateral ethmoidamong citharinids can be homologized with the bony lateral ethmoid strut joining these elementsin most distichodontids. The distichodontid strut passes between the superior and inferior obliquemuscles and arises directly lateral to the olfactory foramen through the lateral ethmoid. Incitharinids, in contrast, the superior and inferior oblique muscles pass between the processesjoining the orbitosphenoid and lateral ethmoid rather than around either or both of them.Furthermore, the lateral ethmoid olfactory foramen is located directly anterior to the centralelongate fenestra between these processes, rather than medial to either of them. Consequently,other than by hypothesizing a highly complex series of alterations of the above bones, musclesand nerves, it is not possible to homologize either of the lateral ethmoid-orbitosphenoid contactsin citharinids with the bony lateral ethmoid strut of distichodontids. Thus it is most parsimoniousto assume that the citharinid and distichodontid types of lateral ethmoid-orbitosphenoidarticulation are distinct, independently acquired, apomorphous systems. Outgroup comparisons have revealed various ostariophysan groups with articulations of thelateral ethmoid and orbitosphenoid somewhat similar to those of citharinids and distichodontids.Some of these in non-characoid ostariophysans (e.g. the bony tube between the orbitosphenoidand lateral ethmoid in the catfish Diplomystes) are undoubtedly convergent with those in thegroups under discussion. Within characoids, however, a direct contact of the lateral ethmoid andorbitosphenoid occurs within African characids in Hydrocynus, Bryconaethiops and variousAlestes species and in the Neotropical families Anostomidae, Curimatidae, Prochilodontidae,Paradontidae and Lebiasinidae. Consequently, the mere fact of a direct articulation betweenthese bones is not a distinguishing character among characoids for either the citharinid or dis-tichodontid type of contact. Nonetheless, in each case the particular form of lateral ethmoid-orbitosphenoid contact appears to be unique to citharinids and distichodontids among characoids. The presence in distichodontids of a strut-like process between the orbitosphenoid and lateralethmoid was noted by Starks (1926, p. 167) in Distichodus fasciolatus, D. lusosso and Mesoboruscrocodilus. The same author also described a somewhat similar tubular process in the Africancharacids Alestes grandisquamis and A. liebrechstii. This process of these characids was laternoted for Hydrocynus, Bryconaethiops, Alestes baremose, A. imberi and A. macrolepidotus byRoberts (1969, p. 441), and has been found in A. dentex and A. macrophthalmus during thesestudies. Although the tubular process in African characids seems homologous with the dis-tichodontid strut on a purely topographical basis, closer observation reveals several majordifferences between these structures. As previously noted, the distichodontid strut is formedprimarily by the lateral ethmoid and covers only the lateral face of the olfactory bulb and tract.The process in the above characids, in contrast, is a bony tube formed primarily or entirely by theorbitosphenoid and completely surrounding the olfactory bulb and tract to varying degrees.Differences between these structures are also apparent in the phylogenetic and ontogeneticdevelopment of the orbitosphenoid tube of characids. Commencing in some Alestes species as ashort anteriorly-directed lip around the orbitosphenoid olfactory foramen, the characid orbito-sphenoid process becomes increasingly elongate anteriorly through the phylogenetic series untilin Hydrocynus it is a thick tube extending to the rear of the lateral ethmoid. At no point duringthis phylogenetic sequence, or the similar ontogenetic transition of Hydrocynus, is there found adistichodontid type strut. Thus the characid tube and the distichodontid strut would appear to beanalogous but non-homologous structures. A closer approximation to distichodontid form of contact between the lateral ethmoid andorbitosphenoid occurs in the South American characoid family Parodontidae. Amongparodontids, the genus Saccodon has a posterior lateral ethmoid process contacting the orbito- CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 283 sphenoid (see Roberts, 1974, Fig. 57). This lateral ethmoid process is rather similar to theXenocharax strut between these elements. In Parodon, in contrast, the expanded contact betweenthese bones is comparable to that of Nannocharax. These similarities are, however, consideredto be convergent with those of distichodontids rather than an indicator of close relationshipbetween the Parodontidae and Distichodontidae (see p. 340). It is interesting to note that distichodontids and parodontids, together with the Africancharacids having a bony tube between the orbitosphenoid and lateral ethmoid all have a forwardshift of the olfactory bulb (see p. 341). It seems likely that the various adaptations of the anteriororbital region in these groups are correlated with this anterior position of the bulb and theconsequent necessity to protect it from compression by the superior and inferior oblique muscles.Similarly, the dorsal and ventral articulations of the lateral ethmoid and orbitosphenoid incitharinids separate the olfactory bulb, nerve and tract from the orbital cavity and the inferiorand superior oblique muscles. The only characoid found during this study to have a forwardposition of the bulb, but lacking some form of bony protection for it, was the Neotropical genusSalminus. However, in that genus the bulb is, nonetheless, surrounded laterally by a very heavy,inflexible connective tissue capsule. An approximation to the citharinid form of contact between the orbitosphenoid and lateralethmoid is found among the Neotropical families Anostomidae, Curimatidae, Prochilodontidaeand Lebiasinidae. A variety of differences discriminate the form of contact in these families fromthat in citharinids. However, rather than dealing with these in detail, for the purposes of thisstudy, it suffices to note that in none of them is the ventral articulation between the orbitosphenoidand lateral ethmoid as massive as in citharinids. Neither has there been found among thesefamilies any form of dorsal contact between the lateral ethmoid and orbitosphenoid comparableto that in citharinids. Citharinids also demonstrate yet another modification of this region of the neurocranium.These genera have a prominent horizontal shelf extending along the rear portion of the orbito-sphenoid and onto the anterior part of the pterosphenoid. The functional significance of thisprocess, which is unique to Citharinus and Citharidium among the families under study, is presentlyunknown. Derived states of the anterior orbital region among citharinids and distichodontids include: 1 the dorsal and ventral lateral ethmoid-orbitosphenoid contacts in citharinids. 2 the bony strut between the orbitosphenoid and lateral ethmoid in distichodontids. Thisstrut is vertically expanded in Nannocharax and Hemigrammocharax, but is hypothesizedto be secondarily reduced in Nannaethiops and Neolebias. 3 the shelf-like process on the lateral surface of the orbitosphenoid and pterosphenoid incitharinids. Posterior orbital and anterior otic regions Among citharinids and distichodontids the posterior orbital and anterior otic regions undergo aseries of interrelated modifications and thus are most easily discussed as a unit. The plesio-morphous state of this portion of the neurocranium, within the complex formed by theCitharinidae and Distichodontidae, is hypothesized to be similar to that of Xenocharax (Fig.10). This genus has the dorsal margin of the orbit formed by a distinct lateral process of the frontal.The posterodorsal wall of the orbital cavity is formed by the prominent sphenotic spine. Thisprocess extends distinctly lateral to the frontal and is orientated along the vertical through thetrigemino-facialis foramen. Ventrolaterally the sphenotic bears a short vertical process which iscontinuous dorsally with the sphenotic spine, and ventrally with the prominent sharp-edgedridge of the lateral commissure of the prootic. This lateral commissural ridge, in turn, contactsthe lateral flange present on the anterior edge of the ascending process of the parasphenoid.Together these lateral processes of the sphenotic, prootic and parasphenoid form a nearlycontinuous, laterally-directed flange at the rear of the orbital cavity. Along its ventral border thesphenotic forms the anterodorsal portion of the hyomandibular fossa which extends anteriorlyto below the sphenotic spine and contacts the posterior edge of the orbital cavity. The prootic inXenocharax is an angular element whose lateral surface nearly forms a right angle horizontally 284 R. P. VARI at the ridge of the lateral commissure. As a consequence the anterior portion of the prootic facesonto the orbital cavity while the posterior section contributes to the lateral surface of the neuro-cranium. In Xenocharax the prootic forms the dorsal and dorsolateral borders of the entranceinto the posterior myodome, and the ventrolateral and ventral borders of the median opening intothe braincase. Thus this bone broadly separates the posteroventral border of the pterosphenoidfrom the dorsal edge of the ascending process of the parasphenoid. Finally, the pterosphenoid andorbitosphenoid of Xenocharax are rather flat, square bones. 5mm para Fig. 10 Xenocharax spilurus, posterior orbital and anterior otic regions, left lateral view. The Xenocharax plan of the posterior orbital and anterior otic regions agrees in generalmorphology, although not necessarily specific detail, with that in non-specialized members ofmost groups of characoids. Thus this plan is hypothesized to represent the plesiomorphouscondition of this region for citharinids and distichodontids. Apart from a difference in the extentof the contribution of the supraorbital to the orbital rim (see p. 301), this arrangement of theposterior orbital and anterior otic regions is shared with minor variations by citharinids and thedistichodontid genera Xenocharax, Nannaelhiops, Neolebias, Paradistichodus and Hemistichodus.The remaining distichodontid genera can be divided into two assemblages on the basis of theirdistinct adaptations of this neurocranial region. Within the subunit of distichodontids formed by Distichodus, Nannocharax and Hemigrammo-charax there occurs a progressive transition from the plesiomorphous ventrally sharp-edgedsphenotic spine to a reduced, ventrally concave sphenotic process. Distichodus species such asD. notospilus retain the plesiomorphous condition of a large, nearly vertical sphenotic spinetapering ventrally to a thin edge. In D. niloticus and D. fasciolatus the central portion of theventral edge of the spine is rotated slightly anteriorly, resulting in an oblique anteroventrallysloping central portion of the ventral margin of the spine. This alteration is further pronouncedin species such as D. lusosso where this section of the sphenotic spine is expanded ventrally intoa broad concave surface. Such a restructuring of the sphenotic spine is carried further in Nanno-charax and Hemigrammocharax where the ventrally reduced spine has the form of a short,ventrally concave, posteroventrally sloping shelf. CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 285 The genera Ichthyborus, Microstomatichthyoborus, Mesoborus, Eugnatichthys, Paraphago,Phago and Belonophago, in turn, exhibit a different series of alterations and reductions of thebones of the posterior orbital and anterior otic regions (note: the osteology of Paraphago, knownonly from the type series of P. restrains, was examined primarily by radiographs). Progressivemodifications of several levels of universality characterize this region of the neurocraniumamong these distichodontids. In the following discussion these adaptations will be dealt withsequentially. First, those apomorphic alterations found in Ichthyborus and common to, or furthermodified in, the other genera listed above will be described. The further derived characters thatcharacterize less universal groups within this unit will be discussed in light of the modifications inIchthyborus. fr par Fig. 11 Ichthyborus besse, posterior orbital and anterior otic regions, left lateral view. The most pronounced alterations of this neurocranial region are those of the sphenotic, inparticular the reduction and reorientation of the sphenotic spine. In Ichthyborus (Fig. 11), theentire sphenotic spine is rotated so that its primitively ventral edge is shifted posterodorsally.This reorientation results in the spine forming a posteroventrally sloping shelf in contrast to itsplesiomorphous state of a nearly vertical wall. In addition, the lateral extent of the spine isreduced, resulting in a truncate process that barely extends beyond the lateral margin of thefrontal. The overall form of the sphenotic in Ichthyborus is horizontally elongate relative to thehypothesized plesiomorphous state. Along with a posterior shift of the prootic, this elongationhas resulted in a horizontal separation of the anterior margin of the hyomandibular fossa fromthe posterior edge of the sphenotic spine and the vertical through the trigemino-facialis foramen.Such a separation is considered derived relative to the close approximation of these structures inthe plesiomorphous condition. The prootic of Ichthyborus is also markedly restructured from theplesiomorphous condition in which the lateral commissure bears a sharp-edged lateral ridge. Inthis genus the prootic is a gently curved, flattened element unelaborated laterally apart from theslightly raised lips around the facialis and trigemino-facialis foramina. The prootic of Ichthyborusis also shifted posteriorly, resulting both in the aforementioned repositioning of the hyo-mandibular fossa and in the reduction of the contribution of the prootic to the edge of theopening into the posterior myodome. As a consequence of the latter change, there is a significantreduction in the plesiomorphously wide separation between the posterior border of the ptero-sphenoid and the ascending arm of the parasphenoid. The final noteworthy adaptation of this neurocranial region in Ichthyborus involves the ventralsurface of the orbital process of the frontal. In citharinids and most distichodontids that portion 286 R. P. VARI of the frontal forming the roof of the orbital cavity is a ventrally smooth, slightly concavesurface; a condition probably plesiomorphous for characoids. The ventral surface of the frontalin Ichthyborus, in contrast, bears a strong transverse ridge capped laterally by an anterodorsalextension of the sphenotic spine. This ridge is continuous with the orbital lamella of the frontaland extends transversely along the ventral surface of the bone just anterior to the suture of thefrontal with the anterodorsal edge of the sphenotic spine. fr sph .-, ;>tm_ , ....... . r^d"^ X,, :'.'. -'il''iSi^BrVV^?:7 X *k.-. ..; ?v'iS^X. v -:A&^-&$$&:.&pro para Fig. 12 Mesoborus crocodilus, posterior orbital and anterior otic regions, left lateral view. These apomorphous modifications of the posterior orbital and anterior otic regions are commonto Ichthyborus and Microstomatichthyoborus, and are the basis for a series of further derivedadaptations in Mesoborus, Eugnatichthys, Paraphago, Phago and Belonophago. Congruent withthe overall elongation of the neurocranium, the orbitosphenoid and pterosphenoid of theselatter genera are notably elongate both relative to the Ichthyborus condition, and more notablywith respect to the hypothesized plesiomorphous characoid state. These taxa also have in commona further restructuring of the sphenotic spine. The primitively ventral edge of the sphenotic hasrotated posterodorsally nearly to the level of the horizontal through the anterodorsal margin ofthe spine. Thus in these genera the spine has the form of a nearly horizontal shelf (Figs 12, 13, 14)rather than the near vertical wall at the rear of the orbital cavity of Xenocharax, or the postero-ventrally slanting process of Ichthyborus. As described earlier, the plesiomorphous sphenoticspine extends distinctly lateral to the edge of the frontal, with Ichthyborus having the lateral extentof the spine significantly reduced. Mesoborus, Eugnatichthys, Paraphago, Phago and Belonophagoshow a further reduction of the Ichthyborus form of the sphenotic. In Mesoborus the sphenoticspine barely extends lateral of the edge of the frontal, and it falls distinctly short of the marginin Eugnatichthys, Paraphago, Phago and Belonophago. Within the latter assemblage, the anteriorsphenotic process which caps the transverse ridge of the frontal is significantly reduced inEugnatichthys and completely lost in Phago and Belonophago (the condition of the process isunknown in Paraphago). In addition, Belonophago lacks, evidently secondarily, the transversestrut along the ventral edge of the frontal that characterizes other members of its monophyleticunit. Phago and Belonophago can be further distinguished within distichodontids by the broadcontact between the posteroventral portion of the pterosphenoid and the dorsal margin of theascending arm of the parasphenoid (Fig. 14). The extensive articulation between these bones CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 287 totally separates the prootic from its plesiomorphous location along the anterior margin of theentrance into the posterior myodome. Furthermore, radiographs of Paraphago rostratus revealwhat appears to be a less extensive suture between these bones. Therefore Phago, Belonophagoand perhaps Paraphago share a synapomorphous contact of the pterosphenoid and parasphenoid.Belonophago is a highly specialized genus characterized by long jaws and an extreme elongationof the skull, particularly in the posterior orbital region (Fig. 14). In this genus the pterosphenoidis expanded posteriorly and ventrally to form the entire anterior surface of the braincase. As aconsequence of this elongation, the lateral commissure and hyomandibular fossa are markedly fr para Fig. 13 Eugnatichthys eetveldii, posterior orbital and anterior otic regions, left lateral view. shifted posteriorly and are removed from the rear of the orbit by a distance equal to the orbitaldiameter. Such an extensive separation is derived relative to the Ichthyborus condition of a slightdistance between these structures, and is a pronounced apomorphous change relative to theplesiomorphous close proximity of the anterior portions of the lateral commissure and hyo-mandibular fossa to the rear of the orbital cavity. As noted previously, the pterosphenoid inBelonophago is broadly in contact posteroventrally with the ascending process of the parasphenoid.In addition, Belonophago has a median articulation between these elements. Arising from theanterior face of the pterosphenoid is a ventrally-directed medial process which contacts a cor-responding dorsally-orientated medial parasphenoid strut. Together these processes form a pediclebetween the pterosphenoid and the parasphenoid (Fig. 14), an adaptation that is evidently uniqueto this genus among characoids. A series of autapomorphous adaptations of the posterior orbital and anterior otic regionsdistinguish Eugnatichthys among distichodontids. The pterosphenoid in this genus is shiftedposteroventrally by the ventral expansion of the orbital lamella of the frontal. This shift, alongwith the horizontal elongation of the sphenotic, results in a marked separation, both verticallyand horizontally, between the rear of the sphenotic spine and anterior margin of the hyo-mandibular fossa. Together with a horizontal expansion of the pterosphenoid, this sphenoticelongation has shifted the prootic and associated lateral commissure posteriorly relative to theIchthyborus condition. Although Eugnatichthys and Belonophago both possess a pronouncedposterior shift of the hyomandibular fossa and lateral commissure, the method by which thisrealignment is achieved differs greatly in the two genera. In Eugnatichthys this restructuring is 288 R. P. VARI primarily a consequence of the elongation of the sphenotic and the ventral expansion of theorbital lamella of the frontal. In Belonophago, in contrast, the realignment is largely the resultof the horizontal extension of the pterosphenoid. bo Fig. 14 Belonophago tinanti, posterior orbital and anterior otic regions, left lateral view. Several modifications of the parasphenoid are of interest for an understanding of relationshipswithin the Citharinidae and Distichodontidae. The plesiomorphous characoid parasphenoidform appears to be a flat, straight or ventrally convex element, extending posteriorly to below thebasioccipital. In Citharinus and Citharidium, in contrast, the parasphenoid is markedly flexedventral to its ascending processes and ontogenetically develops a bulbous process ventral tothis point of flexure. This process serves as the area of attachment for the anteriorly shifted sus-pensory pharyngeals characteristic of this family. Posteriorly the citharinid parasphenoid has twoslightly divergent lateral wings separated by a deep groove. Although such a condition occurs inmany characoids in which the posterior myodome is posteroventrally open, in citharinids themyodome is closed at the rear, and the posterolateral wings of the parasphenoid surround theanterior portion of the dorsal aorta. In juveniles of Citharinus and Citharidium these parasphenoidprocesses are separate both from the basioccipital and the highly modified pars sustentaculumof the Weberian apparatus. In adults, however, the posterior parasphenoid processes fuse dorsallywith the basioccipital and posteriorly with the ventral projections of the pars sustentaculum (seediscussion on the Weberian apparatus). The overall modifications in pharasphenoid form, andthe changes in its relationships to the basioccipital and pars sustentaculum are hypothesized to beapomorphous. The distichodontid genera Eugnatichthys, Paraphago, Phago and Belonophago have theparasphenoid expanded ventrally into a flattened median ridge. This process serves as a point ofattachment for the posteroventrally shifted suspensory pharyngeals occurring in these genera andis most developed in Eugnatichthys in which the shift is most pronounced (Fig. 13). In summary, the hypothesized apomorphous states of the posterior orbital and anterior oticregions in citharinids and distichodontids include: 1 the vertical reduction and horizontal expansion of the sphenotic spine in Hemigrammo-charax, Nannocharax and some Distichodus species. The restructuring of the spine isparticularly pronounced in the first two genera. 2 the lack of lateral flanges on the prootic and ascending arm of the parasphenoid inIchthyborus, Microstomatichthyoborus, Mesoborus, Eugnatichthys, Paraphago, Phago andBelonophago. These genera also share a laterally reduced sphenotic spine whose plesio-morphously ventral edge is shifted posterodorsally; the development of a transverseprocess on the ventral surface of the frontal; a posterior shift of the hyomandibular fossa;and a reduction in the gap between the parasphenoid and pterosphenoid. CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 289 3 the restructuring of the sphenotic spine to form a horizontal shelf in Mesoborus,Eugnatichthys, Paraphago, Phago and Belonophago. The lateral extent of the spine isslightly further reduced relative to the Ichthyborus condition in Mesoborus, and greatlyso in the other genera listed. 4 the reduction of the sphenotic process capping the transverse process of the frontal inEugnatichthys, and its loss in Phago, Belonophago and perhaps Paraphago. 5 the broad articulation between the pterosphenoid and parasphenoid in Phago,Belonophago and perhaps Paraphago, with Belonophago having an autapomorphousmedian contact between these elements. 6 the pronounced posterior expansion of the pterosphenoid in Belonophago. 1 the ventral expansion of the orbital lamella of the frontal and a horizontal lengtheningof the sphenotic in Eugnatichthys. 8 the distinctive flexure in the parasphenoid and the development of a ventral bulbousparasphenoid process in citharinids. In these genera the posterior processes of the para-sphenoid straddle the dorsal aorta and fuse with the pars sustentaculum and basioccipital. 9 the median ventral parasphenoid ridge in Eugnatichthys, Paraphago, Phago andBelonophago. Occipital region The character of phylogenetic interest in the occipital region of citharinids and distichodontidsis the number, form and extent of development of the posttemporal fossae. The most widespread,and the hypothesized plesiomorphous, state of these openings among characoids consists of adorsal and posterolateral pair of fossae on either side of the neurocranium. The horizontal orslightly oblique dorsal fossa is bordered by the supraoccipital medially, the parietal anteriorlyand the epioccipital posteriorly. The remaining fossa is located at the posterolateral corner of theneurocranium and is bordered anteriorly and ventrally by the pterotic, and posteriorly anddorsally by the epioccipital. Citharinids and distichodontids, in contrast, also possess an additional vertically ovate fossabordered by the epioccipital and exoccipital (Fig. 15) (citharinids although possessing this 'third'fossa have, however, lost the dorsal fossa and thus retain only two sets of openings, see below).On the basis of outgroup comparisons the possession of a third fossa appears to be derived amongostariophysans in general and characoids in particular. However, although not widespread, athird posttemporal fossa per se is not unique to citharinids and distichodontids among charcoids.Such a feature has been found in most African characids and among South American characoidsin the families Curimatidae, Hemiodontidae (Roberts, 1974), Parodontidae (Roberts, 1974) andthe characid tribe Cynodontini (sensu Howes, 1976). However, the third posttemporal fossa inthese taxa, with the exception of the Cynodontini, is a small round opening entirely within theepioccipital. This condition contrasts with the large ovoid fossa bordered by the deeply incutexoccipital and epioccipital in citharinids, distichodontids and cynodontines. Although the Cynodontini possess a form of third posttemporal fossa very similar to that ofcitharinids and distichodontids, they do not, however, appear to be the sister group to the latterfamilies. As discussed by Howes (1976), cynodontines possess a series of derived charactersuniting them to the neotropical characid tribe Characini which lacks a third posttemporal fossa.Furthermore, the members of both the Cynodontini and Characini have a rhinosphenoid, anelement unique to various South American characoids, most of which lack any form of thirdposttemporal fossa. In light of the lack of the third fossa both in the sister group to cynodontinesand in the more inclusive unit of Neotropical characoids defined by the presence of a rhino-sphenoid, it is most parsimonious to assume that the cynodontines arose from an ancestorpossessing a rhinosphenoid but lacking a third posttemporal fossa. It thus appears that althoughconvergently derived in cynodontines, the possession of a vertically ovate third posttemporal fossabordered by the epioccipital and exoccipital is apomorphous for, and indicative of the monophylyof the unit formed by citharinids and distichodontids within characoids. The genera Citharinus and Citharidium lack the plesiomorphously present posttemporal fossa 290 R. P. VARI on the posterodorsal surface of the neurocranium. In Eugnatichthys, in turn, there occurs a greatlyreduced fossa in the same area. Both the reduction of the fossa in Eugnatichthys and its loss incitharinids are considered derived in so far as the possession of a large dorsal posttemporal fossais generalized among characoids. Cranial fontanelle The extent of the dorsomedian fontanelle varies considerably within the unit formed by citharinidsand distichodontids. Although the plesiomorphous condition of the fontanelle for these familiesor indeed any otophysans is difficult to ascertain, this variation does permit certain assumptions Ptf, bo 2mm Para- Fig. 15 Xenocharax spilurus, neurocranium, posterior view. to be made. Of particular note is the extension of the fontanelle into the posterior half of thesupraethmoid in Citharinus and Citharidium (Fig. 6c). Such an elongate fontanelle is rarelyencountered among characoids and appears apomorphous for the superfamily. Among disticho-dontids, Xenocharax possesses an elongate fontanelle that separates the frontals, which are onlyin contact at the epiphyseal bar, and the parietals. The remaining distichodontids demonstratea progressive phylogenetic reduction of this extensive fontanelle. All distichodontids apart fromXenocharax have a shorter opening which at the maximum extends slightly anterior to theepiphyseal bar. Ichthyborus, Microstomatichthyoboms, Belonophago, Mesoborus, Eugnatichthys,Paraphago and Phago have a further reduced fontanelle limited to the interparietal region, withthis reduction particularly pronounced in the last four genera. The hypothesis that a progressivereduction of the fontanelle is apomorphic among distichodontids is congruent with the largefontanelle that characterizes the Citharinidae, the family which is hypothesized as the sistergroup to distichodontids. Such a hypothesis also agrees with the distribution of a large suite ofderived characters within distichodontids. This reductional trend appears, however, to have beenslightly reversed in Belonophago where the fontanelle is enlarged relative to the condition in othermembers of its monophyletic group. Suspensorium The diverse modifications of the dentition, jaws and neurocranium that characterize theCitharinidae and subunits of the Distichodontidae are reflected in a series of alterations to thesuspensorium. Two different types of suspensorium can be discriminated among citharinids and CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 291 distichodontids on the basis of the relative position of the articulation of the angulo-articularwith the quadrate. In Citharinus, Citharidium, Xenocharax, Neolebias and Nannaethiops thehorizontal distance between the ventral portion of the hyomandibula and the articular condyleof the quadrate is relatively short. As a consequence, the articulation of the angulo-articular withthe quadrate occurs below the centre of the orbit and distinctly posterior to the vertical throughthe body of the lateral ethmoid. In the remaining distichodontid genera, in contrast, the sym-plectic, metapterygoid and quadrate are relatively elongate resulting in a forward shift of thearticular condyle of the quadrate to below or anterior to the vertical through the lateral ethmoid. The polarity of such changes in the position of the articulation of the angulo-articular withthe quadrate is somewhat problematical in that both anterior and posterior positions of thisjoint occur within a variety of seemingly monophyletic characoid groups. Consequently, a shiftin the position of the articulation has evidently occurred independently within the Characoidea onseveral occasions. It is nonetheless interesting to note that those characoid groups which havebeen considered to be 'primitive' (Hepsetidae and Erythrinidae) have the posterior position ofthis joint; a location also common to generalized members of most characoid groups. If thesefamilies do indeed possess the plesiomorphous jaw form, then the primitive joint position andtype of suspensorium among citharinids and distichodontids would be the posterior articulationcommon to Citharinus, Citharidium, Xenocharax, Neolebias and Nannaethiops. It is furthermorenoteworthy that distichodontids with an anterior articulation of the quadrate and angulo-articularhave derived forms of jaws and dentition. This congruence of the forward position of the angulo-articular-quadrate joint with a series of apomorphous jaw characters, contrasted with the posteriorarticulation among 'primitive' and generalized characoids, supports the hypothesis that ananterior articulation of these elements is the derived condition. These adaptations in the suspensorium are reflective of the relative mouth sizes of the twogroups of genera. In characoids with a non-protrusible mouth, the length of the jaws andconsequently the extent of the gape is primarily a function of the position of the articulation ofthe quadrate with the angulo-articular. Thus in small-mouthed characoids the joint occurs underor forward of the ventral process of the lateral ethmoid. In large-mouthed, often predaciousforms, in contrast, the articulation is distinctly posterior to the lateral ethmoid, and is sometimesalso shifted ventrally. The distichodontid genera Hemistichodus, Microstomatichthyoborus,Mesoborus, Eugnatichthys, Ichthyborus, Paraphago, Phago and Belonophago, particularly thelatter four genera, would appear to invalidate this distinction in being large-gaped fish with aforward angulo-articular-quadrate articulation. However, this seeming incongruity is a functionof the autapomorphous manner in which the elongation of the jaws is achieved in these genera.Among other characoids the premaxilla extends little, if at all, anterior to the tip of the supraeth-moid. Thus the effective gape is a function of the distance between the anterior margin of thesupraethmoid and the articular condyle of the quadrate. In the distichodontid genera notedabove, however, the elongation of the gape is a function of the lengthening of the premaxillaeanterior to the supraethmoid. This adaptation together with the congruent changes in the supra-ethmoid, lower jaw and suspensorium permits an elongation of the gape despite the retention ofan anterior position of the articulation between the angulo-articular and quadrate. In addition to the above broad differences in overall suspensorium form, modifications ofportions of this system characterize groups of varying levels of universality with the Disticho-dontidae. Two multigeneric assemblages within this family demonstrate a restructuring of thegeneralized characoid condition of a somewhat rectangular hyomandibula having a slightlyconcave anterior face. In Nannocharax and Hemigrammocharax the hyomandibula is markedlywidened anteroposteriorly and has a relatively elongate articulation with the hyomandibularfossa (see Daget, 1961, Fig. 10). Ichthyborus, Mesoborus, Microstomatichthyoborus, Eugnatichthys,Paraphago, Phago and Belonophago, in contrast, have an elongate hyomandibula with a deeplyconcave anterior margin (see Daget, 1967, Fig. 9). Both this form of hyomandibula and thatoccurring in the unit formed by Hemigrammocharax and Nannocharax appear to be derivedcharacters serving to define these multigeneric units. The hyomandibula exhibits several other modifications of note among distichodontids. InEugnatichthys this bone has a dorsally-directed process arising from its dorsolateral border 292 R. P. VARI (Fig. 16). A similar, although not as well-developed, process occurs in Phago and appears to bepresent in Paraphago. Eugnatichthys also possesses a medially-directed process on the medialsurface of the hyomandibula. This structure both braces the bone against the ventral surfaceof the neurocranium and serve$ as a point of origin for portions of the adductor mandibulaemuscles. sp Fig. 16 Eugnatichthys eetveldii, posteroventral otic region and dorsal portion of the hyomandibula, left lateral view. The final hyomandibular modifications of note among distichodontids involve the relationshipsof this element to the dorsal portion of the preopercle. Citharinids and distichodontids other thanMesoborus, Eugnatichthys, Paraphago, Phago and Belonophago retain the plesiomorphouscharacoid condition of a slight overlap of the lateral face of the vertical arm of the preopercle bythe posterior border of the hyomandibula. In the listed genera, however, the posterior surfaceof the hyomandibula bears a vertically elongate depression just ventral to the articular condyle.This groove, which appears to be unique to these genera among characoids, tightly surroundsthe dorsal tip of the preopercle (Fig. 17) and further reduces the possibility of motion betweenthese elements. P9P Fig. 17 Phago loricatus, central portion of the hyomandibula and posterodorsal section of the preopercle, left lateral view. CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 293 The preopercle, in turn, has undergone several modifications that distinguish groups of varyinglevels of universality within distichodontids. In Hemistichodus, Ichthyborus, Microstomatich-thyborus, Mesoborus, Eugnatichthys, Paraphago, Phago and Belonophago the laterosensory canalsegment in the vertical arm of the preopercle is shifted medially relative to the condition incitharinids and other distichodontids. This shift, which is especially pronounced in Ichthyborus,results in a broad separation of the laterosensory canal segment from the posterolateral edge of thebone. These genera, with the exception of Ichthyborus and Hemistichodus, are also characterizedby the separation of the posterolateral portion of the preopercle as a distinct dorsally-directedprocess (Fig. 18). Both this lateral preopercular flange and the medial shift of the posterior portionof the preopercular laterosensory canal are hypothesized to be apomorphous characters. pmp 2mmFig. 18 Phago loricatus, posterior portion of the preopercle, left lateral view. The final preopercular modification of note involves the development of a lateral preopercularshelf in some distichodontids. The lateral surface of the preopercle in citharinids and the dis-tichodontid genera Xenocharax, Nannaethiops and Neolebias is nearly flat except for the slightlyraised laterosensory canal. Paradistichodus, Distichodus, Nannocharax, Hemigrammocharax andHemistichodus, in contrast, have a horizontal, laterally-directed ridge along the anterior portionof the preopercle. This lateral preopercular ridge is further elaborated, both posteriorly andlaterally, in Ichthyborus, Microstomatichthyborus, Mesoborus, Eugnatichthys, Paraphago, Phagoand Belonophago where it extends posteriorly to the vertical arm of the preopercle. In these generathese processes of the quadrate and preopercle form a distinct trough from which the expandedorigin of the large A! and A 2 portions of the adductor mandibulae muscles partially arise. Suchan elaboration of the preopercle and quadrate is hypothesized apomorphous for these genera,although occurring evidently independently in the South American characoid familyAnostomidae. The metapterygoid-quadrate fenestra undergoes a series of apomorphic alterations in variousgeneric and multigeneric units among distichodontids. The plesiomorphous condition of thefenestra among characoids appears to be an horizontally ovoid opening bordered primarily bythe metapterygoid dorsally and the quadrate ventrally, and with the symplectic forming a limitedportion of its posteroventral border. A complete eradication of the fenestra occurs in Neolebiasspilotaenia in which the enlarged symplectic fills the space primitively occupied by the fenestra.Correlated with the decreased vertical extent of the suspensorium in Nannocharax and Hemigram-mocharax is a reduction or elimination of the fenestra as a consequence of the approximation ofthe quadrate and metapterygoid (see Daget, 1961, Fig. 10). Hemistichodus, Ichthyborus, Microstomatichthyoborus, Mesoborus, Eugnatichthys, Paraphago,Phago and Belonophago, in contrast, have a horizontally elongate metapterygoid-quadrate 294 R. P. VARI fenestra (see Daget, 1967, Fig. 9). In these genera the contribution of the symplectic to the borderof the fenestra is greatly increased, with a congruent reduction of the portion of the borderformed by the quadrate. Such seemingly apomorphous modifications are correlated with thelengthening of the metapterygoid and symplectic necessitated by the posterior shift of thehyomandibular fossa in these genera. This elongation of the fenestra is particularly pronouncedin Phago and Belonophago in which the bones are exceptionally long and slender. The final modifications of the suspensorium to be discussed involve the relationship of theanterior portion of the suspensorium to the upper jaw. The generalized characoid condition hasa ligamentous or cartilaginous attachment of the palatine to the anteromedial maxillary process,and a loose ligamentous connection of the palatine to the vomerine region. In .Citharinus andCitharidium, however, a large cartilage pad joins the palatine to the anteromedial process of themaxilla. Furthermore, citharinids have a second cartilaginous mass joining the palatine to theposterior surface of the premaxilla. Although a cartilaginous connection between the maxillaand palatine occurs in other characoid groups, both the size of the cartilage in citharinids, andthe presence of a cartilaginous body between the palatine and premaxilla is unique to, and thusconsidered apomorphous for, these genera among the families under study. Some species of Nannocharax, in contradistinction, have a partially ossified cartilaginous rodjoining the palatine to the maxilla. Further study is necessary to determine whether this onto-genetically variable ossification, termed the submaxilla by Daget (1961), is a defining characterfor the genus or some subunit of it. In distichodontids, other than Xenocharax, Nannaethiops, Neolebias and Paradistichodus, themesopterygoid is more tightly joined to the lateral ethmoid than in the hypothesized plesio-morphous condition. Furthermore, the palatine in these genera is distinctly more enveloped bythe ectopterygoid and mesopterygoid than in the generalized state. This trend is most pronouncedin Ichthyborus and the unit formed by Mesoborus, Eugnatichthys, Paraphago, Phago and Belono-phago which have a reduced palatine fitting into a depression along the dorsal surface of theectopterygoid and lacking the plesiomorphous ligamentous attachment to the maxilla. Finally, it should be noted that the quadrate and palatine have been found to be separate in allParadistichodus specimens examined, contrary to Daget (1968, Fig. 10) who illustrated theseelements are fused. In summary, derived characters in the suspensorium of the citharinids and distichodontidsare: 1 the anterior position of the articulation of the angulo-articular and quadrate in alldistichodontids other than Xenocharax, Neolebias and Nannaethiops. 2 the broadened hyomandibula in Hemigrammocharax and Nannocharax. 3 the slender, anteriorly concave hyomandibula in Ichthyborus, Microstomatichthyoborus,Mesoborus, Eugnatichthys, Paraphago, Phago and Belonophago. 4 the dorsolateral and dorsomedial hyomandibular processes present in various dis-tichodontids. 5 the groove on the posterior surface of the hyomandibula in Mesoborus, Eugnatichthys,Paraphago, Phago and Belonophago. 6 the lateral horizontal preopercular shelf in all distichodontids other than Xenocharax,Nannaethiops and Neolebias. This shelf is most distinctly developed, both posteriorlyand laterally, in Ichthyborus, Microstomatichthyoborus, Mesoborus, Eugnatichthys,Paraphago, Phago and Belonophago. 1 the medial shift of the laterosensory canal segment in the vertical arm of the preoperclein Ichthyborus, Microstomatichthyoborus, Mesoborus, Eugnatichthys, Paraphago, Phagoand Belonophago. This assemblage, with the exception of Ichthyborus, is also character-ized by the development laterally of a distinct posterodorsal preopercular flange. 8 the reduction or loss of the metapterygoid-quadrate fenestra in Neolebias spilotaeniaand the unit formed by Nannocharax and Hemigrammocharax. 9 the elongate metapterygoid-quadrate fenestra of Ichthyborus, Mesoborus, Micro-stomatichthyoborus, Eugnatichthys, Paraphago, Phago and Belonophago. CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 295 10 the two large cartilage pads between the palatine and upper jaw of citharinids. 1 1 the increased attachment of the palatine and mesopterygoid to the neurocranium indistichodontids other than Xenocharax, Neolebias, Nannaethiops and Paradistichodus. 12 the loss of the ligamentous connection between the palatine and the maxilla inIchthyborus, Mesoborus, Eugnatichthys, Paraphago, Phago and Belonophago. Opercle On the basis of outgroup comparisons, the plesiomorphous form of the opercle among characoidsis hypothesized to be a flat and unfenestrated bone. Such an opercular form occurs in thedistichodontid genus Xenocharax, but is variously modified in citharinids and all other dis-tichodontids. B Fig. 19 Dorsal portion of the opercle of A. Citharinus citharus (dotted line denotes position of thesuprapreopercle), B. Distichodus notospilus, left lateral view. Laterally the opercle of Citharinus and Citharidium bears a prominent, anterodorsally orientedridge aligned at an acute angle relative to the anterior border of the opercle (Fig. 19a). Thisridge extends dorsally from the body of the opercle to the tip of the elongate anterodorsal cornerof the bone. Such a lateral opercular ridge has not been encountered elsewhere among charcoidsexcept in the Neotropical characoid family Curimatidae (Roberts, 1974). The opercular flange ofcurimatids differs, however, from that of citharinids in its less extensive vertical development,and in not extending to the anterodorsal edge of the bone. Among distichodontids other than Xenocharax, the opercle undergoes a progressivefenestration. The simplest condition of this opening occurs in Nannaethiops and Neolebiaswhich have a series of small, closely apposed holes extending through the opercle. These foramina,which are located slightly posterior to the facet for articulation with the hyomandibula, appearto be the precursors of the distinct opercular fenestra occupying this region in the remainingdistichodontids with the exception of Xenocharax (Fig. 19b). As far as can be determined, neitherthis distinct fenestra nor the series of small openings in Nannaethiops and Neolebias serve for thepassage of any nerves, blood vessels or muscle fibres. In Hemigrammocharax and Nannocharaxthe opercle is reduced dorsally with a consequent opening of the opercular fenestra to the dorsalmargin of the bone. The resultant vertical slit separates the anterodorsal portion of the opercle,to which the dilator operculi muscles attach, from the posterodorsal plate-like portion of the bone.None of these forms of fenestrated opercle have been encountered elsewhere in characoids, oramong the non-characoid ostariophysans examined. Consequently, these modifications areconsidered to represent apomorphous characters of varying levels of universality. In summary, the hypothesized derived opercular characters among citharinids and dis-tichodontids are : 1 the prominent lateral opercular ridge in citharinids. 296 R. P. VARI 2 the fenestrated opercle in all distichodontids other than Xenocharax. Three increasinglyapomorphous forms of the opening occur in these genera: (A) the series of small holes in Nannaethiops and Neolebias. (B) the distinct fenestra of all distichodontids other than Nannaethiops, Neolebias andXenocharax. (C) the vertical slit along the dorsal margin of the opercle in Nannocharax and Hemi-grammocharax. sor psc spo Fig. 20 Xenocharax spilurus, supraorbital, antorbital, infraorbitals, dermosphenotic, pterotic sensorycanal and suprapreopercle, lateral view. Dermosphenotic, pterotic and suprapreopercle The general morphological diversity of the family Citharinidae and Distichodontidae is reflectedin the overall structure and in the patterns of the sensory canals of the dermosphenotic, pteroticand suprapreopercle. Prior to a discussion of these characters, however, it is necessary to commenton the nomenclature of some of the sensory canal-bearing bones of the lateral edge of the skull.Daget, in a series of publications (1958-1968), distinguished the canal-bearing dermosphenoticsand dermopterotics from the underlying sphenotics and pterotics. Similarly, Gregory (1933)and Gregory & Conrad (1938) illustrate a separate dermosphenotic in Distichodus langi,Mesoborus and Phago, and distinguish the scale bone (the dermopterotic of Daget) from theunderlying pterotic. Fig. 21 Citharidium ansorgei, supraorbital, antorbital, infraorbitals, dermosphenotic, pteroticsensory canal and suprapreopercle, lateral view. CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 297 When present the dermosphenotic (or infraorbital 6) of characoids is independent throughoutontogeny from the underlying sphenotic. In light of such a separation, this element shouldobviously be recognized as a distinct bone, the dermosphenotic. However, in none of thecharacoids examined are the pterotic (sensu stricto) and the lateral canal-bearing element (Daget'sdermopterotic and Gregory & Conrad's scale bone) separate elements. Neither has such aseparation been reported in the literature for any adult characoid. Indeed, a separate dermo-pterotic is rare among teleosts (Patterson, 1977, p. 97). Although these elements arise indepen-dently from cartilaginous and intramembranous elements (Weitzman, 1962, p. 25) they fuseearly in ontogeny and I will follow Weitzman in considering the resultant bone as a single unit,the pterotic. The pterotic in this sense is equivalent to the pterotic plus scale bone of Gregory &Conrad, and the pterotic plus dermopterotic of Daget. ant spo Fig. 22 Paradistichodus dimidiatus, supraorbital, antorbital, infraorbitals, dermosphenotic, pteroticsensory canal and suprapreopercle, lateral view. Within the families Citharinidae and Distichodontidae four main patterns of the dermo-sphenotic and pterotic and of their relationships to the infraorbitals and supraperopercle can bediscerned. On the basis of outgroup comparisons, the plesiomorphous form of these bones andthe associated canals among characoids appears to be similar to that of Xenocharax (Fig. 20).The moderately sized dermosphenotic completely roofs over the dilatator fossa and carries aY-shaped segment of the laterosensory canal system. The ventral segment of the dermosphenoticsensory canal communicates with that of the fifth infraorbital, the anterior branch with thesupraorbital sensory canal of the frontal and the posterodorsal section with the pterotic sensorycanal. The pterotic, in turn, is broadly exposed laterally and bears a trifurcate sensory canalsystem. The anterior branch of the pterotic sensory canal contacts the posterior portion of thedermosphenotic sensory canal, the posterior segment communicates with the extrascapularsensory canal, and the ventral branch receives the preopercular sensory canal by way of thesuprapreopercle. ant Fig. 23 Ichthyborus besse, supraorbital, antorbital, infraorbitals, dermosphenotic, pterotic sensorycanal and suprapreopercle, lateral view. 298 R. P. VARI The remaining genera in the families Citharinidae and Distichodontidae exhibit a series ofapomorphous modifications of the above plan of these bones and sensory canals. Citharinus andCitharidium, although retaining the plesiomorphous sensory canal pattern, have greatly reducedthe dermosphenotic into a tube-like element which no longer contacts the edges of the dilatatorfossa and only partially covers the lateral surface of the dilatator operculi muscle (Fig. 21). Incontradistinction, in all distichodontids other than Xenocharax, the dermosphenotic, whenpresent, is posteriorly expanded relative to the hypothesized plesiomorphous condition. As aconsequence of this expansion, the dermosphenotic overlaps much of the primitively exposedlateral surface of the pterotic and separates the suprapreopercle from its direct contact with thepterotic laterosensory canal system (see below with respect to Nannaethiops and Neolebias). spo Fig. 24 Phago intermedius, antorbital, infraorbitals, dermosphenotic, pterotic sensory canal and suprapreopercle, lateral view. This shift of the contact of the suprapreopercle and the expansion of the dermosphenotic resultsin a marked change in the sensory canal system in these bones. Whereas the dermosphenoticsensory canal is bifurcate anteriorly as in Xenocharax, the posterior branch of the canal is drawnout along the horizontally elongate dermosphenotic and bifurcates posteriorly (Figs 22, 23, 24).As a consequence the posteroventral branch of the canal contacts the dorsal tip of the supra-preopercle while the posterodorsal segment communicates with the pterotic sensory canal.This expansion of the dermosphenotic sensory canal results in a horizontally elongate, somewhatH-shaped system. Outgroup comparisons among characoids have failed to reveal a comparableposterior expansion of the dermosphenotic. Neither have there been discovered any othercharacoids in which the dermosphenotic directly communicates both with the infraorbital andpreopercular sensory canal systems. Furthermore, the reduced lateral exposure of the pteroticand the shift in the contact of the suprapreopercle has resulted in a pronounced reduction of thepterotic sensory canal segment. Rather than the plesiomorphous Y-shaped system of mostcharacoids, in these genera the pterotic laterosensory canal is a simple, short tube joining thedermosphenotic and the extrascapular sensory canals. Such a reduction is particularly pronouncedin Mesoborus, Eugnatichthys, Paraphago, Phago and Belonophago in which the laterally exposedportion of the pterotic is a small wedge of bone between the rear of the dermosphenotic and themargin of the extrascapular. Autapomorphous modifications of the above form of dermosphenotic and of the associatedlaterosensory canals characterize several subunits of the assemblage having this pattern of thesebones. In Ichthyborus the dermosphenotic is shifted posterodorsally and thus is totally removedfrom the orbital rim. This shift, along with the dorsal elongation of the suprapreopercle in thisgenus, is reflected in the posteroventral reduction of the dermosphenotic and in the shorteningof the posterodorsal and posteroventral portions of the dermosphenotic sensory canal system(Fig. 23). In Paraphago, in contrast, the dermosphenotic is somewhat expanded ventrally. This CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 299 expansion is a precursor of the markedly expanded dermosphenotic in Phago and Belonophagowhere the large plate-like bone extends ventrally midway along the posterior rim of the orbit(Fig. 24). The enlarged dermosphenotic of Belonophago is autapomorphously further modifiedby the total loss of its sensory canal system. sor spo Fig. 25 Nannaethiops unitaeniatus, supraorbital, antorbital, infraorbitals, dermosphenotic, pteroticsensory canal and suprapreopercle, lateral view. The monophyletic unit formed by Nannaethiops and Neolebias is characterized by a progressiveapomorphic reduction of the dermosphenotic and pterotic sensory canals common to disticho-dontids other than Xenocharax. The least pronounced reduction is found in Nannaethiopsunitaeniatus (Fig. 25) which has a slight shortening of the posteroventral branch of the dermo-sphenotic sensory canal. The reduction of this canal segment, which primitively communicateswith the suprapreopercle, is congruent with the loss of the suprapreopercular sensory canal inNannaethiops and Neolebias (see discussion on the suprapreopercle). The dermosphenotic,pterotic and their sensory canals in Neolebias unifasciatus (see Daget, 1965, Fig. 7) and N.trewavasae are similar to that of Nannaethiops other than for the pronounced reduction or lossof the anterodorsal and posterodorsal branches of the dermosphenotic sensory canal system.Apomorphic reduction of the dermosphenotic laterosensory canals is further advanced in N.trilineatus, N. bidentatus and N. axelrodi where the sensory canals of the dermosphenotic andpterotic are totally lacking. This reductional trend reaches its terminal stage in N. spilotaeniain which the dermosphenotic is lost, together with that portion of the pterotic which plesio-morphously carries the pterotic sensory canal segment. These progressive reductions of thedermosphenotic sensory canals and the eventual loss of the bone itself are considered to be aseries of derived characters of decreasing levels of universality (see the Phylogenetic analysis). The marked modifications of the dermosphenotic and pterotic described above appear to haveresulted in several misinterpretations of distichodontid skull osteology by Gregory & Conrad.In their figure of the skull of Phago (1938, Fig. 35) those authors illustrate the dermosphenoticand pterotic as part of a single ossification. The bone indicated is, however, the dermosphenoticwhich almost totally overlaps the pterotic in this genus. The exposed portion of the pterotic isactually the small scale bone of those workers. The same authors in their drawing of the skull ofMesoborus (1938, Fig. 34), show an unlabelled dermosphenotic which incorporates the sensorycanals of the pterotic and extrascapular along its posterodorsal margin. Examination of thisspecies, however, shows that these sensory canals are actually separate tubes in their respectivebones. In the course of the above discussion, it was noted that the preopercular sensory canal ofcitharinids and distichodontids communicates with the sensory canal system of the pterotic orexpanded dermosphenotic by way of an ossified suprapreopercle. Such a canal-bearing supra-preopercle or a derived form of the bone is common to all citharinids and distichodontids other 300 R. P. VARI than some Neolebias species in which it is hypothesized to be secondarily lost (see below). Thepossession of a suprapreopercle would appear apomorphous in characoids although occurringin a variety of ostariophysan groups. Despite the uncertainty on the exact distribution of thiselement and on the interrelationships of the groups possessing it, at the least, the commonpossession of this element is congruent with the hypothesized monophyletic nature of the unitformed by the families Citharinidae and Distichodontidae. In its simplest form the suprapre-opercle is a bony tube extending from the dorsal opening of the preopercular sensory canal to thesensory canal system of the pterotic or dermosphenotic. Such a suprapreopercular form, whichrepresents an ossification of the primitively unossified tube joining these systems, is modified inthe Citharinidae and subunits of the Distichodontidae. In Citharinus and Citharidium the elongate tube-like suprapreopercle extends over the lateralsurface of the anterodorsal corner of the opercle (Fig. 21). Such a transversing of the opercle bythe suprapreopercle has not been encountered elsewhere among characoids examined and thusappears autapomorphous for these genera. Among distichodontids the plesiomorphous tubularsuprapreopercle is modified in several distinctive apomorphous modes. The simplest of theseadaptations occurs in Ichthyborus besse where the suprapreopercle bears anterodorsal and postero-dorsal flanges that give it a somewhat triangular form (Fig. 23). In Xenocharax, in contrast, thesuprapreopercle retains its basically tubular shape, but is subdivided horizontally into two shorttubes (Fig. 20). The remaining and most radical restructuring of the suprapreopercle occurs inNannaethiops and Neolebias. As illustrated in Fig. 25 for Nannaethiops unitaeniatus these generahave an independent ossification fitting the posteroventrally concave border of the dermosphenotic(see also Daget, 1965, Fig. 7). Although it carries no sensory canal segment, this independentossification is hypothesized to represent a highly modified suprapreopercle. Such an hypothesis iscongruent with its location in the region primitively occupied by the plesiomorphous tubularsuprapreopercle. Furthermore, this element contacts the posteroventral dermosphenotic sensorycanal segment which plesiomorphously communicates with the suprapreopercle. In light of thisassociation and the relative position of the element, it is most parsimonious to assume that thisplate-like, non-canal-bearing element is homologous with the tubular suprapreopercle ofcitharinids and other distichodontids. This flattened suprapreopercle is lost, evidently secondarily,in Neolebias spilotaenia which is characterized by an extreme reduction of various dermal elementsof the skull. Daget, in his illustration of Neolebias unifasciatus (1965, Fig. 7), identified the element hereinconsidered the suprapreopercle as an infraorbital (the postorbital of Daget). It would appear thatDaget believed this bone to be a posteriorly shifted fourth or fifth infraorbital. Such an homologywould give a full series of five infraorbitals plus the dermosphenotic for the species. However,the identification of this independent ossification as an infraorbital appears erroneous if weexamine the infraorbital series of Neolebias trewavasae and Nannaethiops unitaeniatus (Fig. 25).These species, which have the infraorbital reductional trends characteristic of these genera leastpronounced, retain a full series of infraorbitals in addition to the independent ossification termedan infraorbital by Daget. In light of this condition and the previously discussed informationindicating that the independent ossification is a modified suprapreopercle, the identification of theelement as an infraorbital is herein considered incorrect. Hypothesized apomorphic states of the dermosphenotic, pterotic, suprapreopercle and theirassociated sensory canals among citharinids and distichodintids are: 1 the reduced tubular dermosphenotic of citharinids. 2 the posterior expansion of the dermosphenotic in all distichodontids other thanXenocharax. These genera have a congruent reduction of the laterally exposed portionof the pterotic and a shift of the contact of the suprapreopercular sensory canal to thedermosphenotic. 3 the posterodorsal shift of the dermosphenotic in Ichthyborus. 4 the ventral expansion of the dermosphenotic in Paraphago, Phago and Belonophago.This expansion is particularly pronounced in the last two genera. 5 the loss of the dermosphenotic sensory canal system in Belonophago. CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 301 6 the progressive reduction of the dermosphenotic and pterotic sensory canal systems in Nannaethiops and Neolebias.1 the suprapreopercle common to citharinids and distichodontids. 8 the subdivision of the suprapreopercle in Xenocharax. 9 the extension of the suprapreopercle across the opercle in citharinids. 10 the modification of the dermosphenotic into a flat, non-canal-bearing plate in Neolebiasand Nannaethiops. Supraorbital and infraorbitals The hypothetical plesiomorphous infraorbital series for characoids consists of a chain of sixcanal-bearing bones (a dermosphenotic and five infraorbitals) which, together with the supra-orbital, form a bony rim to the orbit. The modifications of the dermosphenotic (infraorbital 6)and its associated sensory canals were discussed in the previous section. Reductions, expansionsand losses of the supraorbital, infraorbitals 1 to 5 and the infraorbital sensory canal systemcharacterize subunits of varying levels of universality among distichodontids. A large supraorbital forming the anterodorsal portion of the orbital rim is common toCitharinus and Citharidium (Fig. 21). Although somewhat enlarged relative to that of manycharacoids, the citharinid form of supraorbital nonetheless appears to be plesiomorphous amongcitharinids and distichodontids in forming a large portion of the anterodorsal rim of the orbit andin extending beyond the posterior margin of the lateral ethmoid. The distichodontid generaXenocharax (Fig. 20), Nannaethiops, Neolebias, Paradistichodus (Fig. 22), Distichodus, Nanno-charax, Hemigrammocharax, Hemistichodus and Ichthyborus (Fig. 23) differ from citharinidsand the generalized characoid condition in having an anteriorly shifted supraorbital which isvariously reduced. The remaining distichodontid genera, in turn, have the supraorbital totallylacking, a loss that is considered apomorphous within distichodontids (in Neolebias spilotaenia,a supraorbital ossification was found only in the largest specimens examined). Although David &Poll's illustration (1937, Fig. 9) of the jaws and dermal bones of the anterior portion of thehead of Microstomatichthyoborus bashforddeani and M. katangae includes a prominent 'supra-orbital', examination of these species has shown that those 'supraorbitals' are actually theantorbitals. Subunits of the Distichodontidae also differ in the total number of infraorbitals, their relativesizes and the extent of the infraorbital sensory canal system. Three different types of reductionfrom a full series of five canal-bearing infraorbitals are discernable in different subunits of thefamily (see the previous section for a discussion of the variation in the dermosphenotic, infra-orbital 6). Two of these reductions result in a partially unossified orbital rim, while the thirdretains a continuous infraorbital series. The first of these modifications to be discussed is the progressive reduction of the infraorbitalseries within the genus Neolebias. Neolebias trewavasae has a full series of five infraorbitals, withtwo elements (infraorbitals 4 and 5) forming the posterior rim of the orbit. In N. unifasciatusand N. bidentatus, in contrast, there is only a single infraorbital at the rear of the orbit, withthe remaining elements shifted so as to retain a fully ossified orbital rim (see Daget, 1965, Fig.7). The remaining infraorbital at the posterior margin of the orbit is lost in N. trilineatus, N.ansorgei, N. axelrodi and N. spilotaenia in which the posterior orbital border is unossified. Thisreductional trend reaches its terminal stage in N. spilotaenia which additionally lacks infraorbitals2 and 3 and the sensory canal segment in infraorbital 1. The progressive reduction of the infra-orbital series from a chain of five canal-bearing elements to a single non-canal-bearing bone isconsidered to represent a series of derived reductional characters of varying levels of universality,and is congruent with the overall reduction of the dermal skull elements in these genera. The second reduction of the infraorbital series among distichodontids occurs in Nannocharaxand Hemigrammocharax. In Nannocharax multifasciatus, N.fasciatus (Daget, 1961, Fig. 7) andHemigrammocharax wittei the fourth and fifth infraorbitals are reduced to two bony tubes dorsalto an expanded third infraorbital. In contrast, the specimens of Nannocharax niloticus, N.ansorgei, N. gobioides, N. intermedius, Hemigrammocharax machadoi and H. polli examined have 302 R. P. VARI infraorbitals 4 and 5 totally lacking. Although this reduction results in an unossified posteriororbital border similar to that in some Neolebias species, the phylogenetic sequence of thereductions and losses leading up to this condition differ significantly from that in Neolebias.Consequently, the unossified posterior orbital rim in the listed Nannocharax and Hemigram-mocharax species and that of the previously noted Neolebias species are considered to be non-homologous. ant 1mm Fig. 26 Eugnatichthys eetveldii, antorbital, infraorbitals, dermosphenotic, pterotic sensory canal and suprapreopercle, lateral view. The final reductional transition scries of the infraorbitals among distichodontids occurs withinthe assemblage consisting of Ichthyborus, Microstomatichthyoborus, Mesoborus, Eugnatichthys,Paraphago, Phago and Belonophago. Contrary to the hypothesized plesiomorphous conditionof an infraorbital series with five elements, these genera are characterized by a maximum of fourinfraorbitals. This reduced infraorbital count appears to be a consequence of the loss of aninfraorbital at the posterior margin of the orbit. The exact homology of the remaining element,that is whether it represents the plesiomorphous infraorbital 4, infraorbital 5 or a fusion of thesebones, is uncertain. However, for simplicity in the following discussion the bone is arbitrarilytermed infraorbital 4. Within this assemblage, Ichthyborus (Fig. 23) has a relatively narrowinfraorbital series, but with infraorbital 4 expanded posterodorsally so as to separate distinctlythe dermosphenotic from the orbital rim. In contrast, Microstomatichthyoborus, Mesoborus,Eugnatichthys (Fig. 26), Paraphago, Phago (Fig. 24) and Belonophago have the posterior infra-orbital elements widened, with infraorbital 3 expanded posteriorly so as to cover a major portionof the cheek. Anteroventrally infraorbital 3 is produced into a distinct process extending ventralto infraorbital 2 and almost to the vertical through the articular condyle of the quadrate. Withinthis assemblage Paraphago has the fourth infraorbital reduced to a narrow, horizontally elongateelement and it is completely lacking in Phago (Fig. 24) and Belonophago. As a consequence ofthese changes the enlarged third infraorbital of Phago and Belonophago completely covers thecheek and is in direct contact dorsally with the expanded dermosphenotic. Among members ofthese families, the enlarged third infraorbital in Belonophago is also unique in its total lack of asensory canal segment. The loss of infraorbitals 4 and 5 in these genera differs from that among thepreviously described Neolebias, Nannocharax and Hemigrammocharax species in that the ex-pansion of the remaining infraorbitals fills the space primitively occupied by the missing elements,and a fully ossified orbital rim is thus retained. Two differences between the observations of this study and those of Gregory & Conrad (1938)and Daget (1968) should be noted. In their illustration of the skull of Mesoborus, Gregory &Conrad (1938, Fig. 34) show a single infraorbital (the suborbital of those authors) in the regionplesiomorphously occupied by infraorbitals 1 and 2. However, examination of the specimenprobably illustrated by those workers, along with other Mesoborus material, shows there to betwo distinct infraorbitals preceding the expanded infraorbital 3. Similarly, Daget (1968, Fig. 4) CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 303 in his illustration of the skull of Hemistichodus vaillanti shows a single large infraorbital in theregion normally occupied by infraorbitals 2 and 3. However, all specimens of the three nominalHemistichodus species examined have the second and third infraorbitals as separate elements. In summary, hypothesized apomorphous supraorbital and infraorbital characters amongdistichodontids are: 1 the reduction and anterior shift of the supraorbital in Xenocharax, Nannaethiops,Neolebias, Paradistichodus, Distichodus, Nannocharax, Hemigrammocharax andIchthyborus. This reduction is a precursor of the further apomorphous loss of theelement in Microstomatichthyoborus, Mesoborus, Eugnatichthys, Paraphago, Phago andBelonophago. 2 the reduction to a single infraorbital at the rear of the orbit in Neolebias unifasciatusand N. bidentatus, with the remaining element lost in N. trilineatus, N. ansorgei, N.axelrodi and N. spilotaenia. 3 the loss of infraorbitals 2 and 3 and the sensory canal of infraorbital 1 in N. spilotaenia. 4 the reduction of infraorbitals 4 and 5 to bony tubes or a loss of these elements inNannocharax and Hemigrammocharax. 5 the loss of infraorbital 5 in Ichthyborus, Microstomatichthyoborus, Mesoborus, Eugna-tichthys, Paraphago, Phago and Belonophago. 6 the expansion of infraorbital 4 to exclude the dermosphenotic from the orbital rim inIchthyborus. 7 the reduction of infraorbital 4 in Paraphago and its loss in Phago and Belonophago. 8 the loss of the sensory canal segment of infraorbital 3 in Belonophago. 9 the anterior and posterior expansion of infraorbital 3 in Microstomatichthyoborus,Eugnatichthys, Mesoborus, Paraphago, Phago and Belonophago. Branchial apparatus The morphology of the branchial apparatus among members of the families Citharinidae andDistichodontidae demonstrates a significant degree of variation for a system that is otherwiserather stable among characoids. Major branchial apparatus modifications occur in Citharinusand Citharidium, whereas less pronounced adaptations distinguish various distichodontid sub-units. The fifth ceratobranchial (lower pharyngeal) of citharinids is highly modified with respect tothe relatively flat, anteromedially tooth-bearing elements common to most characoids. InCitharinus and Citharidium the medial portion of the fifth ceratobranchial is a dorsally bulbous,highly fenestrated structure bearing only a few greatly reduced, loosely attached teeth (Fig. 27).These genera also demonstrate a comparable reduction and modification of the upper pharyngealtooth plates and their associated dentition. Among most characoids, the fourth epibranchialand cartilaginous fourth pharyngobranchial articulate with the tooth-bearing fourth and fifthupper pharyngeal tooth plates respectively (see Rosen, 1973, Fig. 3). In contradistinction,citharinids either have the upper pharyngeal dentition totally lacking or reduced to a few loosely-attached minute spicules. More significantly, the fourth and fifth upper pharyngeal tooth platesof citharinids are fused to form an elongate bony plate (Fig. 28). Such a distinctive upper pharyn-geal ossification has not been encountered elsewhere among characoids and would appear to beapomorphous, as is its edentulous nature. Similarly, the highly modified lower pharyngeals ofCitharinus and Citharidium are, as best as can be determined, autapomorphous for these generaamong characoids. Further apomorphic characters in the branchial apparatus of citharinidsinclude their loss of the first pharyngobranchial and the elongation and reorientation of thesecond and third pharyngobranchials. These alterations result in a close approximation of thetips of the first epibranchial and the second and third pharyngobranchials. The marked restructuring of the branchial apparatus among citharinids would seem to be anadaptation to their filter-feeding mode of life. An additional gill arch character congruent withthis feeding method is the presence of micro-gillrakers in all citharinids. Micro-gillrakers are aseries of parallel bands of small, bony spicules located along both faces of the gill arch between 304 R. P. VARI the gillrakers and gill filaments (Gosse, 1956; Daget, 1962). On the basis of our present knowledgeon micro-gillraker distribution, it appears that these structures are unique to citharinids amongcharacoids. 1mmFig. 27 Citharidium ansorgei, fifth ceratobranchial, right side, medial portion enlarged, dorsal view. Alterations of the branchial apparatus among distichodontids are not as radical as those incitharinids and are primarily reductional. In most Neolebias species the fourth upper pharyngealtooth plate is slightly ossified, with this element and its associated dentition totally lacking in N.spilotaenia (Fig. 29). Furthermore, in N. spilotaenia the fifth upper pharyngeal tooth plate is areduced rounded ossification bearing approximately only six teeth. Similarly, the tooth-bearingportion of the lower pharyngeals is reduced to a small ovoid patch with a correlated reduction inthe number of teeth. Pb Fig. 28 Citharidium ansorgei, gill arches, dorsal parts of right side, ventral view. An ossified fourth upper pharyngeal tooth plate and its associated dentition is also lacking inHemigrammocharax machadoi, Nannocharax fasciatus and N. niloticus. However, based on themost parsimonious reconstruction of the phylogeny of citharinids and distichodontids, this lossis considered to have occurred independently of that in Neolebias. Furthermore, it is noteworthythat the lack of a fourth upper pharyngeal tooth plate is not universal within Nannocharax.Nannocharax intermedius has a small, slightly ossified fourth upper pharyngeal tooth plate, CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 305 whereas TV. gobioides and N. ansorgei have a larger but still reduced form of the bone. The resolu-tion of the question of whether this variation in the extent of the ossification of this elementrepresents a phylogenetic reductional trend within the genus or whether it is a function ofontogenetic variation awaits further study. up. Fig. 29 Neolebias spilotaenia, gill arches, dorsal parts of right side, ventral view. Among the remaining distichodontid genera no alterations of branchial apparatus structurehave been found. However, congruent with their restructured neurocranial form, Ichthyborus,Microstomatichthyoborus, Mesoborus, Eugnatichthys, Paraphago, Phago and Belonophago havea posterior shift in the attachment of the suspensory pharyngeals to the neurocranium. Withinthis assemblage Mesoborus, Eugnatichthys, Paraphago, Phago and Belonophago have an additionalshift of this attachment ventrally, a trend that is most pronounced in the latter four genera wherethe pharyngeal attachment is to the previously described median parasphenoid ridge. It wouldappear that these shifts of gill arch attachment in these genera are a function of the extension ofthe adductor mandibulae muscle onto the medial surface of the hyomandibula and its expansioninto regions plesiomorphously occupied by the branchial apparatus. In summary, hypothesized derived states of the branchial apparatus among citharinids anddistichodontids are : 1 the highly fenestrated, dorsally bulbous, nearly edentulous lower pharyngeal incitharinids. 2 the fusion of the fourth and fifth upper pharyngeal tooth plates in citharinids. 3 the loss of the first pharyngobranchial and the anterior elongation of the second and thirdpharyngobranchials in citharinids. 4 the loss of the fourth upper pharyngeal tooth plate and its associated dentition inNeolebias spilotaenia. This species also demonstrates a reduction of the fifth upperpharyngeal tooth plate and of the dentition associated with that element and the fifthceratobranchial. 5 the micro-gillrakers in citharinids. 6 the reduction or loss of the fourth upper pharyngeal tooth plate in various Nannocharaxand Hemigrammocharax species. 7 the posterior shift of the attachment of the suspensory pharyngeals in Ichthyborus,Microstomatichthyoborus, Mesoborus, Eugnatichthys, Paraphago, Phago and Belonophago. 8 the ventral shift of the suspensory pharyngeals onto the median parasphenoid ridge inEugnatichthys, Paraphago, Phago and Belonophago. Weberian apparatus The common possession of the Weberian apparatus, an otophysic connection between theanterior chamber of the swimbladder and the middle ear, characterizes the series Otophysi of 306 R. P. VARI the superorder Ostariophysi (Rosen & Greenwood, 1970). The Weberian apparatus is composedof the Weberian ossicles (the pars auditum) and their supporting vertebrae (the pars sus-tentaculum). The Weberian ossicles are four small bones, the tripus, intercalarium, scaphiumand claustram (the intercalarium and claustrum are lacking in some groups), that are joinedby ligamentous bands and pivot on the anterior vertebrae. It is believed that vibrations inducedin the anterior chamber of the swimbladder by soundwaves in the surrounding medium aretransmitted by these ossicles to the middle ear, thereby aiding in sound reception (see Alexander,1966, for a discussion of the mechanism). The pars sustentaculum is derived from the four ormore anterior vertebrae and serves as a base for the Weberian ossicles and the shortened firstpleural rib. In the generalized characoid condition the vertebrae of the pars sustentaculum are QS v \ vpv cts v / V p v 1mm Fig. 30 Nannaethiops unitaeniatus, posteroventral section of neurocranium, ventral portion of parssustentaculum and connective tissue sheath, left lateral view, Weberian ossicles removed. ventrally unfused and unmodified, with the fourth vertebrae bearing a pair of shortened,modified pleural ribs. Arising from the medial surface of each of these ribs is a distinct process, theos suspensorium, which serves for the support and attachment of the peritoneal layer of theanterior swimbladder chamber. The dorsal aorta, which is in contact with the ventral surface ofthese vertebrae, is surrounded laterally and to varying degrees ventrally by the shortened firstpleural rib and os suspensorium. All characoids examined have a triangular connective tissue system associated with the parssustentaculum, the anterior section of the coeliac artery and the peritoneal covering of the anteriorchamber of the swimbladder. This complex (Fig. 30) arises anterodorsally from the parasphenoidand basioccipital and posterodorsally from the os suspensorium. Dorsally it encompasses thedorsal aorta and anteriorly surrounds the anterior portion of the coeliac artery. The posteriorsection of this complex is formed by a medial thickening in the peritoneal covering over theanterior swimbladder chamber. This connective tissue band extends from the os suspensoriumto the point of contact of the coeliac artery with the anterodorsal surface of the swimbladderchamber. Alexander (1962) applied the term 'coeliac sheath' to that portion of the system en-compassing the coeliac artery in the Neotropical characoid genus Leporinus. In the followingdiscussion, however, the term sheath is applied to the entire complex, unless a specific section(e.g. coeliac sheath) is cited. Although the Weberian apparatus, particularly portions of the pars sustentaculum, undergoespronounced restructuring in various ostariophysan groups (see Alexander, 1962, \964a, 19646)it has been traditionally considered morphologically conservative among characoids. However,an examination of the Weberian apparatus in the families Citharinidae and Distichodontidae hasrevealed a series of modifications of the pars sustentaculum, os suspensorium and of theirrelationships to the connective tissue sheath. Four major types of modifications to this complex CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 307 are distinguishable in these families. These are hereafter termed the Nannaethiops, Citharinus,Xenocharax and Nannocharax types of pars sustentaculum. Nannaethiops possesses the simplest form of modification to the pars sustentaculum and ossuspensorium in the families Citharinidae and Distichodontidae. In the Nannaethiops type parssustentaculum (Fig. 30) the second and third vertebrae bear paired, ventrally-directed projectionsarising from their ventrolateral borders, contrary to the plesiomorphous, ventrally unelaboratedstate of these bones. Furthermore, the os suspensorium in Nannaethiops is enlarged and extendsanteriorly to contact the posterior margin of the ventral process of the third vertebra. The ventralprojections of the second and third vertebrae, together with this anterior process of the ossuspensorium, form a longitudinally orientated vertical wall lateral to the dorsal aorta. This bo cts ICO Fig. 31 Citharinus citharus, juvenile, posteroventral section of neurocranium, ventral portion ofpars sustentaculum, connective tissue sheath and independent coeliac ossifications, left lateral view,Weberian ossicles removed. structure also serves as a broad area of attachment for the connective tissue sheath associatedwith the dorsal aorta and coeliac artery. Such adaptations, either in the Nannaethiops form orfurther derived states, are common to all species of the families Citharinidae and Distichodon-tidae. On the basis of their unique nature within characoids these modifications are hypothesizedas being synapomorphous for these families. As noted previously, the Nannaethiops type of pars sustentaculum and os suspensorium is theontogenetic precursor of more complex structures in citharinids and some other distichodontids.One of the more elaborate alterations of this system is common to Citharinus and Citharidium.In the smallest individuals of Citharinus examined, the pars sustentaculum is similar to theNannaethiops type other than for the slightly more anteroventrally expanded os suspensoriumand a pair of slight ossifications along the anterior surface of the coeliac sheath. Later in ontogeny,juveniles of Citharinus and Citharidium possess the pars sustentaculum and os suspensoriumform illustrated in Fig. 31. The ventral processes of the second and third vertebrae are moreanteroventrally produced than in the Nannaethiops pattern or earlier in ontogeny. Similarly,the os suspensorium is anteroventrally expanded into a prominent, ventrally-directed processthat partially encompasses the connective tissue band on the anteromedial surface of the swim-bladder. The os suspensorium is also expanded anterodorsally to surround the lateral surface ofthe dorsal aorta and tightly contact the rear of the expanded ventral process of the third vertebrae 308 R. P. VARI Finally, the coeliac sheath is encompassed anteroventrally by a prominent ossification derivedfrom the independent ossifications present earlier in ontogeny. With increasing age the os suspensorium, the ventral process of the second and third vertebraeand the independent ossifications of the coeliac sheath coalesce with each other and with theposterior projections of the parasphenoid and ventral projections of the basioccipital. In largeindividuals of Citharinus and Citharidium this results in a triangular, highly ossified structurewhich corresponds in shape to, and largely replaces, the connective tissue sheath present earlierin ontogeny (Fig. 32). This complex is anteriorly continuous with the elongate posterior ramusof the parasphenoid and encompasses the dorsal aorta laterally, ventral to the first three vertebrae. Fig. 32 Citharinus citharus, adult, posteroventral section of neurocranium and ventral portion ofpars sustentaculum complex, left lateral view, Weberian ossicles removed. The dotted line indicatesthe position of the anterior chamber of the swimbladder. Similarly, the coeliac artery is surrounded laterally and ventrally from its divergence from thedorsal aorta to its point of contact with the peritoneal covering of the anterior chamber of theswimbladder. Posteriorly the third portion of this structure consists of a thick bony strut formedby a ventral projection of the os suspensorium. This portion of the complex serves as an expandedarea of attachment for the peritoneal layer covering the anterior swimbladder chamber. Thesemodifications of the pars sustentaculum and os suspensorium, together with the strong attachmentof the neural process of the Weberian apparatus to the supraoccipital, eliminate any possibilityof motion, either between the vertebrae forming the pars sustentaculum or between the parssustentaculum and the skull. With increasing age, these ossifications expand further so that in thelargest citharinid examined (a skull of Citharinus citharus, 170 mm from snout to rear of thefourth vertebrae) the processes surrounding the dorsal aorta and coeliac arterly are nearly incontact with their fellows along the internal midline of the complex. Examination of the Weberian apparatus in characoid outgroups has failed to reveal modifica-tions homologous to those of citharinids, nor have such adaptations been encountered amongother ostariophysans. An analogous envelopment of the dorsal aorta and coeliac sheath has beenfound in the Neotropical characoid genera Anostomus, Leporinus, Schizodon and Laemolyta. Inthese genera the parasphenoid bears posteriorly-directed processes which laterally encompassthe dorsal aorta ventral to the basioccipital and first vertebra. In large individuals of these genera,these parasphenoid processes extend posteroventrally along the lateral surface of the strongly CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 309 developed coeliac sheath, and an independent ossification overlies the dorsal aorta laterallyunder the first three vertebrae. Although similar in superficial form to those of citharinids, theseossifications in anostomids differ in their ontogenetic origins and are thus considered non-homologous with those of citharinids although synapomorphous for some or all anostomids. bp Fig. 33 1mm Xenocharax spilurus, posteroventral section of neurocranium and ventral portion of parssustentaculum, left lateral view, Weberian ossicles removed. The second apomorphous modification of the Nannaethiops type of pars sustentaculum and ossuspensorium occurs in the monotypic distichodontid genus Xenocharax. In this species thelongitudinal axis of the first four vertebrae is strongly angled posterodorsally with respect to theskull and anteroventrally relative to the longitudinal axis through the remaining abdominalvertebrae (Fig. 33). The shift in the axis of these vertebrae is reflected in two adaptations. Firstly,the axis through the chain of the Weberian ossicles is nearly horizontal in Xenocharax, rather thandemonstrating the posteroventral slope generalized for characoids. This shift is, however, aconsequence of the reorientation of the anterior vertebrae with respect to the skull, rather than arepositioning of the ossicles relative to the pars sustentaculum. The second adaptation of theXenocharax os suspensorium is consequent upon the retention by this genus of the primitiverelationship of the os suspensorium and the anterior chamber of the swimbladder. Due to thereorientation of the pars sustentaculum with respect to the vertebral column, this alignmentrepresents a marked decrease in the angle between the axis of the os suspensorium and that ofthe longitudinal axis of the vertebrae of the pars sustentaculum. This alteration is of sufficientmagnitude so that the ventral tip of the os suspensorium extends to below the first or secondvertebrae. This contrasts to the generalized characoid condition where it reaches only to belowthe third vertebra. The fourth and final form of pars sustentaculum among citharinids and distichodontids occursin some Nannocharax species. The species of this genus range from moderately deep-bodied,generalized forms such as N. multifasciatus, N. ansorgei and TV. minutus to ventrally-flattened,bottom-dwelling species such as N. brevis, N. gobioides, N. niloticus and N. intermedius. One ofthe myriad adaptions to a bottom-dwelling habit demonstrated by the latter group of species is arestructuring of the pars sustentaculum and the first and second pleural ribs. GeneralizedNannocharax species have the basically Nannaethiops type of pars sustentaculum. In the specializedforms, however, the proximal section of the first pleural rib is expanded anteriorly to form aprominent flange extending over the dorsal surface of the anterior swimbladder chamber. Thesecond pleural rib has a similar, though posteriorly-directed and somewhat smaller, processproximally. Further distally this rib also bears an anteriorly directed flange extending along the 310 R. P. VARI lateral wall of the anterior chamber of the swimbladder. More notably, the ventral processesof the second vertebra are expanded into a common, transverse, plate-like structure covering theanterior and anteroventral surfaces of the anterior chamber of the swimbladder (Fig. 34).Associated with these expanded ventral processes of the second vertebra is the development of abony tube along the anteromedial face of this plate. This canal surrounds the coeliac artery fromits point of origin to the point where, plesiomorphously, it contacts the anterior chamber of theswimbladder. It should be emphasized that although superficially similar to the bony tube aroundthe coeliac artery in citharinids, this channel in Nannocharax is formed by a process of the secondvertebra rather than by the citharinid independent ossifications. ac pc Fig. 34 Nannocharax niloticus, swimbladder and bony capsule of anterior swimbladder chamber, ventral view. Such an encapsulation of the anterior swimbladder chamber has not been reported previouslyamong characoids or encountered elsewhere in the superfamily during this study and undoubtedlyrepresents a synapomorphy for some Nannocharax species. Functionally, this partial encapsula-tion of the swimbladder appears to be related to the bottom-dwelling habits of the speciespossessing it, as is the case in cobitids, various catfish groups and perhaps the small capsulesaround the anterior swimbladder chamber in some gymnotids (e.g. Rhamphichthys rostratus). Derived states of the Weberian apparatus in the families Citharinidae and Distichodontidaeare: 1 the expanded os suspensorium and the ventrolateral projections of the second and thirdvertebrae common to all citharinids and distichodontids at some point in ontogeny. 2 the highly ossified triangular pars sustentaculum complex of citharinids. 3 the marked reduction in the angle between the axis of the os suspensorium and that of thepars sustentaculum in Xenocharax. 4 the expansion of the ventral processes of the second vertebra and modifications of thefirst and second pleural rib to partially encapsulate the anterior chamber of the swim-bladder in some Nannocharax species. Postcleithra The pectoral girdle of citharinids and distichodontids is distinctive in having a maximum of twopostcleithra rather than the three postcleithral elements that characterize most characoids. Theupper postcleithrum in these families overlaps the junction between the cleithrum and supra-cleithrum and is homologous with the element termed postcleithrum 1 in Byrcon meeki by CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 311 Weitzman (1962). The remaining postcleithrum in citharinids and distichodontids is locatedposteromedial to the cleithmm and has the form of an elongate plate with a pronounced antero-ventral strut that is ventrally continuous with a rod-like process (Fig. 35a) (see also below withrespect to Phago and Belonophago). In overall form this postcleithral element is very similar tothe flat, ovoid postcleithrum 2 and the separate rod-like postcleithrum 3 overlapping and ventralto the former that occupy this region in most characoids. Because of this similarity in form,the ventral postcleithral element of citharinids and distichodontids is hypothesized to representan apomorphous, fused postcleithrum 2 and 3. Nannocharax and Hemigrammocharax, in addition,lack the dorsal postcleithral element (postcleithrum 1) that plesiomorphously overlies thejunction between the cleithrum and supracleithrum. A final postcleithral character of note inthese families is the expansion of the ventral postcleithral element in Phago and Belonophago toform a rigid strut around the posterior border of the pectoral fin base (Fig. 35b). A B Fig. 35 Cleithrum and postcleithra of A. Citharidium ansorgei, B. Phago intermedius. Pelvic bone The form of the pelvic bone shows considerable variation from the generalized characoid con-dition both throughout and within the assemblage that constitutes the families Citharinidae andDistichodontidae. The pelvic bone of anotophysans and generalized characoids has anteriorlya single tapering process braced by a longitudinal ridge. However, among citharinids and parti-cularly distichodontids, the pelvic bone has two anterior processes giving it an anteriorly bifurcateform (Fig. 36a). The longer lateral process extends almost directly anteriorly and bears alongitudinal ridge along its dorsal surface. The smaller medially slanting process, in turn, has ashorter ventral ridge. A somewhat bifurcate pelvic bone also occurs in various neotropicalcharacoid groups, but in none of them is the bifurcation as pronounced as that in citharinids anddistichodontids. Further modifications to the pelvic bone occur in bottom-dwelling Nannocharax species (N.niloticus, N. gobioides, N. intermedius and N. fasciatus) in which the pelvic bone is distinctlywidened anteriorly to form a broad plate-like structure (Fig. 36b). This modification, the con-gruent expansion of the ischiac process of the pelvic bone and the elongation of the pelvic finrays is evidently an adaptation to the bottom-dwelling habits of these species. Caudal skeleton The caudal skeleton of citharinids and distichodontids exhibit several characters of interest both 312 R. P. VARI Fig. 36 Pelvic girdle of A. Xenocharax spilurus, B. Nannocharax niloticus. relative to the question of the monophyletic nature of the complex formed by these families andto the hypothesis of relationships within the assemblage. The hypural fan form hypothesizedplesiomorphous for characoids consists of six separate hypural elements. All citharinids anddistichodontids differ from this condition in having hypurals 1 and 2 (the ventral elements) fusedinto a single unit not articulating with the fused PUj and U l (Fig. 37). Such an apomorphic fusion of the two ventral hypurals also occurs within the Characoidea inthe South American family Hemiodontidae (including Anodus), the characid subfamily Ser-rasalminae and the African characid Lepidarchus adonis (Roberts, 1966). As noted earlier the 1mm Fig. 37 Xenocharax spilurus, caudal skeleton. CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 313 members of the Hemiodontidae possess a rhinosphenoid; an apomorphous median ossificationunique to various Neotropical characoids. With the exception of hemiodontids, all members ofthese rhinosphenoid-bearing groups examined during this study have separate hypurals. Similarly,although the exact relationships of the Serrasalminae are unknown, their multicuspidate dentitionties them to various Neotropical groups which lack any hypural fusions. Finally, Lepidarchusis a member of the African Characidae (Roberts, 1966) whose members are otherwise character-ized by six separate hypurals. Two other South American characoid groups have fused hypurals 1 and 2. However, in eachof these cases the fused hypural plate differs from that of citharinids and distichodontids in sucha way as to cast doubt on the homology of this fusion with that in the latter families. In theCynodontini the genera Hydrolycus and Cynodon have hypurals 1, 2 and 3 joined into a largeplate encompassing the ventral and part of the dorsal portions of the hypural fan. However, thecynodontine genus Rhaphiodon, has hypurals 2 and 3 fused, but separate from hypural 1. Finally,Roestes, the most plesiomorphous cynodontine (Howes, 1976), has a completely separate hypuralfan. Thus it is most parsimonious to assume that the phylogenetic progression of hypural fusionof cynodontines is a joining of hypurals 2 and 3 followed by the fusion of the resultant plate withhypural 1 . Such a sequence does not demonstrate a fusion homologous with the fused hypurals1 and 2 that characterize citharinids and distichodontids. Finally, fused hypurals 1 and 2 havealso been discovered in Crenuchus and Poecilocharax. The fused hypurals in these genera differ,however, from the pattern in citharinids and distichodontids in being joined to the fused PU Xand Uj. The number of separate hypural elements is further reduced in Neolebias, Nannaethiops andParadistichodus in which only three upper hypurals exist. Although the question of whether thisreduction is a consequence of the fusion of hypurals 5 and 6, or a loss of the latter, has notbeen resolved, such a reduction is nonetheless considered to be a derived feature. Finally, areduction from the two epurals plesiomorphous for citharinids and distichodontids has occurredin Paradistichodus, Phago and Belonophago in which only one epural is present. Scale form Unlike most anatomical features, the scale form among members of the Characoidea exhibitslittle variation at the gross morphological level. The majority of characoids are characterized bythe possession of a simple cycloid scale form. Within the families Citharinidae and Distichodon-tidae, however, this seemingly plesiomorphous scale form is limited to the genus Citharinus.Citharidium has ctenoid scales, while all distichodontids have a second, non-homologous form ofserrate scales. In Citharidium the prominent, distinctly pointed ctenii are continuous with the main body ofthe scale (Fig. 38a). In this scale form a strong ridge extends from the scale body radially along thecentre of each cteni, with the distal circuli diverging outwards along the ridge. The members ofthe family Distichodontidae, in contrast, possess a very different type of ctenoid scale, thesimplest form of which is illustrated in Fig. 38b. In the distichodontid ctenoid scale, the scalebody is comparable to that of a typical characoid scale except for a shift of the scale focus towardsthe scale margin. Along the scale margin there occurs a line of irregular ctenii that vary in numberbetween different taxa. These ctenii differ from those of Citharidium in being formed by a seriesof independent ossifications attached to the scale body and each other by unossified connectivetissue. Examination of the ctenoid scales reported in other characoid groups has shown the term to beapplied to an assemblage of very different scale types characterized by various forms of serrateposterior margins. In Cynopotamus and other genera in the Neotropical tribe Characini thectenoid nature of the scales is a consequence of a series of spicules along the posterior margin andexposed lateral surface of the scale. The ctenoid scales of the tetragonopterine Ctenobrycon,various curimatids and the prochilodontid genus Prochilodus are characterized by an irregularlynotched posterior scale margin, whereas the curimatid genus Psectrogaster has definite althoughsomewhat irregular ctenii. However, none of the above forms of ctenoid scales is comparable 314 R. P. VARI CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 315 to those in the African families under discussion. In the South American genus Ctenolucius thescales bear strong ctenii formed primarily by posterior continuations of the pronounced ridgesthat radiate outwards from the focus. In the closely related Boulengerella a less well-developedform of the same scale type occurs. Although these scale types approximate to that in Citharidiwn,they differ in the form of the ridges and in possessing strong radii which are totally lacking in thatgenus. These differences and the large number of derived characters uniting Citharidiwn into amonophyletic unit with Citharinus (which retains the plesiomorphous cycloid scale form) supportthe hypothesis that the Ctenolucius and citharinid forms of ctenoid scales were acquired indepen-dently. 5mm aa /-k-i TFig. 39 Xenocharax spilurus, superficial cranial musculature, lateral view. Although the distichodontid form of ctenoid scale does not appear to be approximated withincharacoids, a similar ctenoid scale with serrations formed by a series of independent ossificationsoccurs in the anatopysan ostariophysan Gonorhynchus greyi. However, the similarity in scaleform between such phylogenetically separated members of the Ostariophysi undoubtedly rep-resents independent acquisitions. The distichodontid form of ctenoid scale undergoes further modifications in the genera Phagoand Belonophago. In these taxa the greatly thickened scales and strong connective tissue bandsjoining them result in a bony but flexible body covering. Furthermore, as a consequence of theirelongate cylindriform bodies, the relatively large scales in these genera are distinctly flexedhorizontally. This flexure is especially pronounced in the vertically elongate scales of Phago.Phago and Belonophago have a distinct ossified bump overlying the scale focus, with this structureproduced into a posteriorly directed spinous process in Belonophago (Fig. 38c). The final character of note in the scalation of these families is the form and extent of develop-ment of the lateral line system. Although the plesiomorphous lateral line form among characoidsis unknown, it is noteworthy that citharinids and distichodontids have a straight or nearly straightlateral line. This contrasts with the distinctly ventrally-curved lateral line in all other African andmost Neotropical characoids. A reduction from a complete lateral line occurs in all Neolebiasand Hemigrammocharax species. However, Roberts (1967) has questioned whether the reducedlateral line of Hemigrammocharax represents single or multiple reductions from the completelateral line of Nannocharax. Two species of Hemistichodus (lootensi and mesmaekersi) have adistinctive medially interrupted lateral line. Myology The osteological characters described above have included a variety of alterations of the jaws, the 316 R. P. VARI jaw suspensorium, the operculum and the parts of the neurocranium associated with these systems.Congruent with these osteological changes are a series of adaptations in the cheek and opercularmusculature of these genera. In the following discussion the musculature of the distichodontid genus Xenocharax will firstbe described in detail. As far as can be determined from outgroup comparisons to generalizedcharacoids, the myological plan of Xenocharax is the least derived overall among citharinids anddistichodontids. Thus it serves as a useful basis of comparison for the myological variation thatoccurs in these families. In the case of Paraphago, which is known only from two syntypes andwhich was consequently not examined myologically, it is assumed that the myological charactersof the genus are congruent with those of its monophyletic group. The muscles providing informa-tion relevant to a reconstruction of the hypothesized phylogeny of citharinids and distichodontidsare the adductor mandibulae, the levator arcus palatini and the dilatator operculi. The adductor mandibulae in Xenocharax (Fig. 39) is composed of sections A 1} A 2 (divisibleinto medial and lateral portions), A 3 and A w . The A x portion of the adductor mandibulae is asomewhat tubular muscle extending anterodorsally from its origin on the lateral flange of thehorizontal process of the quadrate. It is dorsally encompassed by a connective tissue sheathcontinuous with the strong tendon that runs along the anterior surface of the muscle. This tendon,in turn, inserts onto the maxilla at the point of merger between the anteromedial maxillary processand the broad lateral plate of the bone. The remainder of the adductor mandibulae consists of the two sections of the A 2 portion of themuscle and medial to these an A 3 . Posteriorly the two portions of the A 2 arise in common fromthe lateral face of the hyomandibula and vertical ramus of the preopercle. Along their postero-dorsal borders these portions of the muscle contact the ventrolateral face of the dorsally widenedlevator arcus palatini. Ventrally A 2 has an origin from the lateral face of the horizontal portionof the preopercle and the posteroventral process of the quadrate (the medial portion of A 2does not arise from the latter element). The A 2 divides into two sections parasagittally slightlyanterior to the point where the levator arcus palatini passes between the A 2 and A 3 portions of theadductor mandibulae. The lateral section of A 2 extends forward over the posterodorsal surfaceof A! to insert onto the posterior edge of the dentary, just dorsal to the articulation of that elementwith the angulo-articular. The medial portion of A 2 , in contrast, has its anterodorsal surfaceinvested by a connective tissue band that is continuous with a prominent tendon extendinganteriorly from the forward tip of the muscle and joining a comparable tendon from the A 3 .This common tendon inserts onto the A w and the coronomeckelian ossification (Fig. 40). TheA 3 section of the adductor mandibulae is posteriorly separated from the medial section of A 2by the ventral portion of the levator arcus palatini. The A 3 arises from the anteromedial surfaceof the hyomandibula and is surrounded anteriorly by a connective tissue sheath that is continuouswith the tendon arising from the medial section of A 2 . Finally, the A w (intramandibular) sectionof the adductor mandibulae is a relatively flat muscle filling the meckelian fossa and attaching tothe angulo-articular and dentary. The levator arcus palatini of Xenocharax is a triangular muscle, laterally exposed along theposterodorsal region of the cheek. From its origin on the posteroventral portion of the sphenoticspine the levator arcus palatini extends ventrally between A 3 and the medial section of A 2 to inserton the anteroventral portion of the hyomandibula. The dilatator operculi is a pinnate musclearising from the broad dilatator fossa of the sphenotic and pterotic and inserting onto a raisedridge along the anterodorsal corner of the opercle. The above pattern of cheek and opercular musculature is common to Xenocharax, Nannaethiopsand Neolebias. Citharinids and other distichodontids differ to varying degrees from the Xeno-charax cheek musculature pattern. This variation in muscle origins, insertions, proportions andinterconnections serves to define a series of multigeneric units within these families. Citharinus and Citharidium have an elongate A x portion of the adductor mandibulae with amore extensive origin on the horizontal process of the quadrate and the ventral arm of thepreopercle than in the Xenocharax condition (Fig. 41). More significantly, the citharinid Ajdiffers from that of Xenocharax in attaching directly to the rear of the dentary rather than ten-dinously to the maxilla. Citharinids have, however, a ligament running from the point of contact CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 317 of the A! with the dentary to the region of the maxilla where the tendon of A x inserts in Xeno-charax. This ligament, the ligamentum primordiale of previous authors, may be homologous tothe tendinous band along the anterior surface of the A x section of the adductor mandibulae inXenocharax. On the basis of outgroup comparisons, the citharinid insertion of the A x to thedentary in conjunction with the retention of a distinct ligamentum primordiale is hypothesizedto be the plesiomorphous characoid condition. The derived attachment of the A x to the maxillain Xenocharax together with the seeming incorporation of the ligamentum primordiale intoits tendon is evidently correlated with the increased upper jaw mobility of distichodontids. den Fig. 40 Xenocharax spilurus, adductor mandibulae, anterior portions, medial view. The A 2 portion of the adductor mandibulae in Citharinus and Citharidium arises posteriorlyfrom the lateral surfaces of the hyomandibula and preopercle, but does not extend as dorsal onthese elements as in Xenocharax. Anteriorly the lateral portion of the A 2 in citharinids insertsonto the rear of the A w through a tendon that is anteriorly continuous with that of the medialsection of A 2 . This common insertion contrasts with the separate attachment of these muscles onthe dentary and A w respectively in Xenocharax. That portion of the adductor mandibulae ofcitharinids comparable to the A 3 of Xenocharax (that portion of the muscle medial to the levatorarcus palatini) is greatly reduced and usually has the form of a series of muscle slips arising fromthe hyomandibula and metapterygoid. Furthermore, rather than having a distinct tendon,anteriorly continuous with the anterior tendon of A 2 , the slips of muscles forming the A 3 ofcitharinids attach individually along the inner surface of the medial portion of A 2 . The A w section of the adductor mandibulae in Citharinus and Citharidium is greatly expandedto fill entirely the large meckelian fossa and extends dorsally over the upper edge of the dentary.The levator arcus palatini of these genera, although relatively longer than in Xenocharax, has asimilar origin and insertion apart from an expanded insertion posterodorsally on the preopercle.The dilatator operculi is significantly larger than that of Xenocharax and totally fills the largedilatator fossa on the sphenotic, pterotic and lateral edge of the frontal. This pinnate muscleinserts on the distinctive, elongate opercular spine that extends anterodorsally towards themiddle of the fossa in citharinids. Within distichodontids, several genera and generic assemblages show various modificationsof the Xenocharax pattern of cheek musculature. In Paradistichodus the overall proportions of themuscles are changed, perhaps as a consequence of the elongate head that characterizes the genus.The A x portion of the adductor mandibulae is notably elongate and the muscle extends along thetendon anterodorsally, nearly to the maxilla. Overall, the A 2 is smaller than in Xenocharax andarises solely from the ventral half of the preopercle and hyomandibula. This reduction of the A 2is especially notable in the longitudinal extent of the lateral section of the muscle which con-sequently attaches to the dentary through an elongate tendon. Distichodus, Nannocharax and Hemigrammocharax have a series of modifications of theadductor mandibulae correlated with their unique jaw morphology (Fig. 42). The elongate A x 318 R. P. VARI pmx den LP a'a pof Fig. 41 Citharinus citharus, superficial cranial musculature, lateral view. portion of this muscle arises from the quadrate and extends anteriorly to attach to the maxillaby way of a ligament running across the lateral face of the dorsally expanded dentary. As inXenocharax the A 2 section of the adductor mandibulae is subdivided into medial and lateralsegments with a prominent A 3 also present. However, as a consequence of the radically re-structured jaw form of these genera, the relationships between the sections of the adductormandibulae are somewhat altered. In other distichodontids the anterior sections of A 2 and A 3run in parallel and the lateral portion of A 2 inserts lateral to, or only slightly dorsolateral to, thepoint where the joined tendon of A 3 and the medial portion of A 2 contacts the A w . In Dis-tichodus, Nannocharax and Hemigrammocharax, in contrast, the insertion of the lateral portionof A 2 is distinctly dorsal to the level where the combined tendon from A 3 and the medial sectionof A 2 attach onto the coronomeckelian ossification. The A w of Distichodus, Nannocharax andHemigrammocharax arises from the dorsal edge of the latter tendon and extends from distinctlyposterior of the rear of the angulo-articular forward onto the bone. Both the origin of the A wsolely from the dorsal border of the ligament and its posterior position relative to the angulo-articular appear apomorphous relative to the generalized characoid condition. An additional 5mm pmax den 2-m '2-| PP Fig. 42 Distichodus lusosso, superficial cranial musculature, lateral view. Dashed line on maxillaindicates attachment of ligamentum primordiale. CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 319 consequence of these osteological and myological alterations is a shift of the relative position ofthe ligamentum primordiale and the tendon of Aj. Instead of running in common or parallel asin the plesiomorphous condition, the connective tissue bands in these genera cross at right angles,with the tendon of A x passing over the ligamentum primordiale. pmx m OOP Fig. 43 Ichthyborus quadrilineatus, superficial cranial musculature, lateral view. As discussed earlier the ventral edge of the sphenotic spine undergoes a progressive phylo-genetic enlargement within the unit formed by Distichodus, Hemigrammocharax and Nannocharax.Congruent with this alteration of the spine is an expansion in the extent of the origin of thelevator arcus palatini. This trend is especially pronounced in Nannocharax and Hemigrammo-charax in which the broad ventrally concave sphenotic process serves as an expanded area oforigin for the levator arcus palatini. Furthermore, in these genera the dilatator operculi ratherthan having the hypothesized plesiomorphous origin from the dilatator fossa has a broad attach-ment to the lateral surface of the sphenotic. This shift from the generalized characoid condition iscarried further in some of the larger Nannocharax species examined (N.fasciatus and N. elongatus). 5mm aa A-| q pop Fig. 44 Ichthyborus besse, adductor mandibulae, lateral view. In these species the anterior portion of the dilatator operculi arises from the anterior face of thesphenotic and passes medial to the levator arcus palatini to insert on the anterodorsal process ofthe opercle. The broad, shallow depression on the sphenotic and pterotic of Nannocharax andHemigrammocharax does not serve as a dilatator fossa, but is instead occupied by the plate-likedermosphenotic present in these genera. 320 R. P. VARI The remaining distichodontid genera, Hemistichodus, Ichthyborus, Microstomatichthyoborus,Mesoborus, Eugnatichthys, Paraphago, Phago and Belonophago, have the A x portion, of theadductor mandibulae arising from the trough formed by the lateral processes of the quadrate andpreopercle. This muscle inserts on the posterolateral and posterior surface of the angulo-articular(Figs 43, 44). Such an insertion differs radically from the tendinous attachment of this musclesection to the maxilla in all other distichodontids. This change and the congruent loss of a 5mm LAP a pop Fig. 45 Ichthyborus ornatus, adductor mandibulae, lateral view, A t portion removed. definitive ligamentum primordiale appears consequent upon the radically altered upper jawmorphology of these genera. These changes result in the elimination of the functional advantagethat an attachment of the A x to the maxilla provides in less derived forms of distichodontidjaws. These genera, with the exception of Hemistichodus, also have a significantly enlarged originof the adductor mandibulae on the lateral and medial surfaces of the hyomandibula and thelateroventral portions of the sphenotic and pterotic. This expanded origin is particularly pro-nounced in Eugnatichthys. Within the above assemblage, both Ichthyborus and Eugnatichthys present further apomorphicmyological characters. The A x of Ichthyborus besse is distinctive in having its lateral portionautapomorphously altered into a distinct triangular muscle slip which attaches to the lateralportion of A 2 via a connective tissue band (Fig. 44). In addition, all Ichthyborus species are dis-tinctive among distichodontids in having the lateral portion of the A 2 inserting on the angulo-articular, contrary to the plesiomorphous attachment of this muscle segment on the dentary.This insertion is through an elongate anterior tendon in Ichthyborus ornatus, I. monodi and /.quadrilineatus (Fig. 45) and by way of the aforementioned modified section of the A x in /. besse(Fig. 44). Eugnatichthys has the primitively single A 3 portion of the adductor mandibulae parasagittallysubdivided into two sections. The lateral portion of the A 3 in this genus extends anteriorly to jointhe medial section of A 2 and inserts in common with that muscle directly on the dentary. Thisinsertion contrasts with the plesiomorphous insertion of the A 3 on the coronomeckelian ossifica-tion, an insertion that is retained by the medial portion of the A 3 section of the adductormandibulae of Eugnatichthys. The levator arcus palatini in Ichthyborus, Microstomatichthyoborus, Mesoborus, Eugnatichthys,Paraphago, Phago and Belonophago has an apomorphous expanded origin on the ventral(primitively anterior) surface of the posteroventrally sloping or horizontal sphenotic spinecharacteristic of these genera. Phago and Belonophago, in turn, have the muscle origin furtherexpanded onto the ventral face of the frontal in the posterodorsal orbital region; an adaptationunique to these genera among characoids examined. Finally, the levator arcus palatini of CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 321 Eugnatichthys, Phago and Belonophago has a distinctly reduced vertical extent relative to that ofother distichodontids and consequently does not directly insert onto the hyomandibula. Instead,these genera have the muscle inserting onto that element via a broad aponeuroses. In summary, hypothesized derived states of the adductor mandibulae, levator arcus palatiniand dilatator operculi among citharinids and distichodontids are: 1 the insertion of the Aj portion of the adductor mandibulae on the maxilla in Xenocharax,Neolebias, Nannaethiops, Paradistichodus, Distichodus, Nannocharax and Hemigram-mocharax. This attachment is hypothesized, however, to have been secondarily lost inall other distichodontids. 2 the insertion of the lateral section of the A 2 portion of the adductor mandibulae to theA w via a tendon in citharinids. 3 the reduction of the A 3 portion of the adductor mandibulae in citharinids. 4 the greatly expanded A w portion of the adductor mandibulae in citharinids. 5 the expanded dilatator operculi in citharinids. 6 the reduced lateral portion of the A 2 section of the adductor mandibulae in Para-distichodus. 1 the elongation of the A l portion of the adductor mandibulae in Distichodus, Nannocharaxand Hemigrammocharax. 8 the relatively dorsal insertion of the lateral portion of A 2 in Distichodus, Nannocharaxand Hemigrammocharax. 9 the posterior origin and expanded extent of the A w portion of the adductor mandibulaein Distichodus, Nannocharax and Hemigrammocharax. 10 the expanded origin of the levator arcus palatini on the ventrally broadened sphenoticspine in Nannocharax, Hemigrammocharax and some Distichodus species. 1 1 the shift of the origin of the dilatator operculi to the lateral surface of the sphenoticin Nannocharax and Hemigrammocharax. 12 the insertion of the lateral portion of the A 2 on the angulo-articular in Ichthyborus. 13 the expansion of the origin of the A 2 section of the adductor mandibulae onto the medialsurface of the hyomandibula and ventral surfaces of the pterotic and sphenotic inIchthyborus, Microstomatichthyoborus, Mesoborus, Eugnatichthys, Paraphago, Phagoand Belonophago. These genera also have the origin of the levator arcus palatini expandedonto the anterior surface of the sphenotic spine. 14 the partial origin of the levator arcus palatini from the ventral surface of the frontal inPhago and Belonophago. 15 the reduction of the vertical extent of the levator arcus palatini and its insertion on thehyomandibula through an aponeuroses in Eugnatichthys, Phago and Belonophago. Swimbladder, intestinal and epibranchial organ forms Swimbladder Within the assemblage consisting of the Citharinidae and Distichodontidae, the form of both theanterior and posterior chambers of the Swimbladder undergoes several modifications. Thegeneralized Swimbladder morphology in characoids consists of two chambers connected by ashort narrow tube. The rotund anterior chamber is slightly elongate and is attached by theperitoneal layer surrounding it to the os suspensorium and the triangular connective tissuecomplex associated with the pars sustentaculum of the Weberian apparatus. The posteriorchamber is of slightly greater diameter than the anterior and several times the longitudinal extent.Although the plesiomorphous relative proportions of the chambers of the Swimbladder amongcharacoids is presently unknown, it is noteworthy that in both citharinids and distichodontids theposterior chamber of the swimbladder is distinctly elongate with respect to the anterior (approxi-mately four times the longitudinal length). Despite this uncertainty about the phylogeneticpolarity of an elongate posterior swimbladder chamber, the possession of such a structure is,nonetheless, at least congruent with the hypothesis of the monophyly of the unit formed by 322 R. P. VARI citharinids and distichodontids among characoids. Is should be emphasized, however, that evenif apomorphous for characoids, such an elongate posterior chamber of the swimbladder is alsocharacteristic of the South American characoid family Hemiodontidae and occurs in variousforms in some Neotropical characids (e.g. Iguanodectinae, see Vari, 1977). Within the Distichodontidae, the evenly curved oblong anterior and elongate posterior swim-bladder chambers that are plesiomorphous for the family are modified in Hemigrammocharaxand Nannocharax. These genera have anteriorly-directed diverticulae of the anterior swimbladderchamber. These diverticulae extend from the anterior face of the chamber lateral to the ventralprocess of the os suspensorium and the posterior portion of the triangular connective tissuecomplex associated with the pars sustentaculum. The extent of these diverticulae range from theslight bulges of Hemigrammocharax and generalized Nannocharax species to the pronouncedanterior diverticulae found in specialized Nannocharax species such as N. niloticus, N. gobioidesand N. intermedius. The latter Nannocharax species also have the posterior swimbladder chambergreatly reduced to a small tubular structure (Fig. 34) ; an adaptation evidently correlated with theirbottom-dwelling habits. Intestinal form Two modifications of the morphology and convolution patterns of the intestinal tract distinguishcitharinids within the complex formed by the families Citharinidae and Distichodontidae. On thebasis of information from ontogenetic and outgroup comparisons, the plesiomorphous form of theintestinal tract among characoids appears to be a moderately looping, smooth-walled system.In both Citharinits and Citharidium, however, the intestine is elaborated into a highly convolutedsystem (see Daget, 1962, Fig. 9) characterized by distinctive multiple outpocketings of its terminalloop. Whereas the elongation of the intestine is evidently correlated with the microphagoushabits of these genera, the functional significance of the intestinal outpocketings is obscure. Epibranchial organ form Epibranchial organs of differing levels of complexity have been described for a variety of Neo-tropical and African characoids (see Nelson, 1967, p. 73). Within the families under discussion,a slightly developed diverticula in the posterior portion of the gill arches has been reported amongdistichodontids in Paradistichodus (Daget, 1958, p. 1368), Distichodus (Daget, 1959, p. 1289),Xenocharax (Daget, 1960, p. 41), Nannocharax (Daget, 1961, p. 172) and Neolebias (Daget, 1965,p. 9). The structure has also been found in Nannaethiops and Hemigrammocharax during thisstudy. Daget reported that the epibranchial organ was absent in Ichthyborus besse (1967, p. 145)and Hemistichodus (1968, p. 16). This study has also found such outpocketings to be lacking inthe remaining Ichthyborus species, Microstomatichthyoborus, Mesoborus, Eugnatichthys, Phagoand Belonophago. The lack of epibranchial organs in these genera is considered to be an apo-morphous secondary loss on the basis of the presence of such outpocketings in the Citharinidae,which is the sister group to distichodontids, and in all other distichodontids. Citharinus and Citharidium, in contrast, have greatly elaborated epibranchial organs. In thesegenera the diverticulae are expanded into lobulate muscular structures (Fig. 46) with ramifyinginternal chambers supported by spicules of bone (see Daget, 1962a, Figs 7, 8). Prominent epi-branchial organs also occur in the Neotropical characoid families Prochilodontidae andCurimatidae. In neither of those families, however, are these outpocketings as greatly developedas they are in citharinids. Neither do the epibranchial organs of the Neotropical groups have thedistinctive lobed forms of those in the Citharinidae. Thus the form of the citharinid epibranchialorgans is considered synapomorphous for Citharinus and Citharidium among characoids. Olfactory bulbs Among anotophysans and most characoids the olfactory bulb lies immediately anterior to, andin contact with, the telencephalon and is laterally enclosed by the orbitosphenoid. In this statethe olfactory nerve passes anteriorly either through the anteromedial opening in the orbito-sphenoid or through foramina in that bone, and extends anterolaterally to the olfactory foramen CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 323 of the lateral ethmoid. Citharinids and distichodontids, in contrast, have the olfactory bulbsshifted anteriorly to contact or nearly contact the posterior surface of the lateral ethmoid. Thisshift in olfactory bulb position results in a shortening of the olfactory nerve and an elongation ofthe olfactory tract. These alterations of the olfactory system are hypothesized apomorphous forthese families within characoids. This hypothesis is based both on the widespread distribution of aposterior position of the olfactory bulb among teleosts in general and characoids in particular,and on the ontogenetic anterior movement of the bulb that has been observed in variouscitharinids and distichodontids. Fig. 46 Citharidium ansorgei, epibranchial organ,left lateral view. Although an anterior position of the olfactory bulb is generalized for cyprinoids and siluroids,among characoids examined during this study such a forward location of the bulb has been foundonly in citharinids, distichodontids, the genus Salminus, some african characids and the familyParodontidae. Adults of Salminus maxillosus have the olfactory bulb immediately posterior ofthe lateral ethmoid, a shift evidently reflected in ontogeny since young S. hilarii have the olfactorybulb relatively more posteriorly located. The significance of the forward position of the olfactorybulb for an understanding of the relationships of these enigmatic South American characoidsto citharinids and distichodontids is difficult to ascertain. Indeed, it is notable that this genuslacks all other hypothesized derived characters synapomorphous for the Citharinidae andDistichodontidae. Within the African Characidae the hypothesized plesiomorphous posterior position of the bulbhas been found in Micralestes (M. acutidens, M. lualabae, M. voltae and M. occidental is),Phenacogrammus interruptus, Rhabdalestes tangensis, Virilia pabrensis and some Alestes species(A. sadleri and A. longipinnis). A slight separation between the bulb and telencephalon is found inAlestes lateralis and A. imberi, and the bulb has a distinct anterior shift in Hydrocynus, Bryconae-thiops and a variety of Alestes species (A. dentex, A. baremose, A. liebrechstii, A. macrophthalmus,A. macrolepidotus, A. nurse and A. rhodopleurd). This progressive anterior movement in theposition of the olfactory bulb within a group that forms a monophyletic unit within theCharacidae (see p. 341) was evidently acquired independently of that in citharinids and dis-tichodontids. Finally, within the Parodontidae a slight forward shift of the bulb has been found inParodon bimaculatus and Apareidon qffinis. The significance of the Parodontidae in the questionof the relationships of the families under discussion is reviewed later. 324 R. P. VARI Phylogenetic reconstruction The preceding descriptions of various osteological and soft anatomical systems have discusseda series of characters providing information relevant to a reconstruction of a hypothesis of genericrelationships within the assemblage consisting of the Citharinidae and Distichodontidae. Thefollowing discussion deals first with the synapomorphies for the complex formed by citharinidsand distichodontids, followed by those derived characters that distinguish subunits of decreasinglevels of universality within this assemblage. The resultant phylogeny and its implication for theclassification of these families is discussed subsequently. The most parsimonious hypothesis of relationships based on the derived characters analysedpreviously is presented in Fig. 47. The apomorphous characters defining the genera and supra-generic assemblages are numbered sequentially, since such a procedure simplifies the visualizationof character distribution and generic relationships. The numbering of the characters correspondsto the numbered synapomorphies of the cladogram in Fig. 47. Relationships at the subgenericlevel are discussed in detail for only five of the taxa recognized in this study (Neolebias, Ichthyborus,Distichodus, Nannocharax and Hemigrammocharax) in so far as the conclusions reached in thiswork are congruent with or at least fail to refute the hypotheses of relationships inherent in theprevious definitions of the remaining genera. The characters synapomorphous for subgenericunits in Neolebias and Ichthyborus are incorporated into the cladograms presented in Fig. 48 and49. Families Citharinidae and Distichodontidae The hypothesized monophyly of the assemblage formed by the Citharinidae and Distichodontidaeis supported by the following synapomorphies of these families: 1 the ventral elaborations of the second and third vertebrae and the ventral expansion ofthe os suspensorium. 2 the bicuspidate tooth form. 3 the fusion of postcleithra 2 and 3. 4 the bifurcate pelvic bone. 5 the fusion of hypurals 1 and 2. 6 the lack of a premaxillary ascending process. 7 the possession of a premaxillary articular fossa. 8 the lack of lateral supraethmoid wings. 9 the lack of a distinct supraethmoid spine. 10 the trifurcate articular complex at the anterior margin of the supraethmoid. 11 the large, ventrally ovate third posttemporal fossa bordered by the epioccipital andexoccipital. 12 the anterior shift of the olfactory lobe. 13 the possession of a suprapreopercle. 14 the lack of an interdigitating symphyseal hinge. As discussed in the anatomical descriptions, some of the above characters are evidently uniqueto these families among characoids, whereas others are approximated in characoid outgroups.On the basis of available information, the first four characters would appear to be autapo-morphous for the unit formed by the Citharinidae and Distichodontidae among characoids.Characters similar to five to twelve occur in other characoid groups. However, available evidenceindicates that their presence in these outgroups is a consequence of convergence rather than theresult of immediate common ancestry. Finally, characters 13 and 14, though hypothesized asderived, also occur in characoid groups whose affinities are uncertain at present and thus arepossibly sister groups to the unit consisting of citharinids and distichodontids. In addition tothe characters listed above, it should also be noted that citharinids and distichodontids have astraight lateral line and an elongate posterior swimbladder chamber, characters whose polarityis, however, presently undetermined. Within the hypothesized monophyletic assemblage defined by the characters detailed above,two families, the Citharinidae and Distichodontidae, are recognized in this study. Citharinids CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 325 BCDEFGHIJKLMNOPQ -.199-206197-198 Fig. 47 Cladogram of the most parsimonious hypothesis of relationships in the families Citharinidaeand Distichodontidae. Taxa (solid circles): A, Citharidium; B, Citharinus; C. Xenocharax; D,Nannaethiops; E, Neolebias; F, Parodist ichodus; G, Distichodus; H, Nannocharax; I, Hemigram-mocharax; J, Hemistichodus ; K, Ichthyborus; L, Microstomatichthyoborus ; M, Mesoborus; N,Eugnatichthys; O, Paraphago; P, Phago; and Q, Belonophago. Synapomorphies 1-206 correspondto those of the text. 326 R. p. VARI are a highly specialized group characterized by a series of distinctive synapomorphies, but havinglittle intrafamilial variation. Indeed, the differences between citharinid species are primarilymeristic and morphometric other than for the single character autapomorphous for each of thecontained genera. In contrast, the Distichodontidae, although characterized by few synapo-morphies, is very speciose and exhibits a pronounced degree of intrafamilial variation. Thesignificance of these diametrically opposed trends in citharinids and distichodontids is obscureand indeed may only be a function of the differing speciation and extinction rates in these familiesas viewed at this particular point in time. Family Citharinidae As mentioned above, the family Citharinidae is distinguished by a multitude of apomorphouscharacters. The derived features of citharinids are nearly all related to the pronounced re-structuring of the pars sustentaculum and the alterations in their ingestive and digestive systemscorrelated with their microphagous habits. These characters, in summary, are: 15 the marked expansion of the ventral processes of the second and third vertebrae and ossuspensorium. 16 the independent ossification along the anterior and lateral surfaces of the coeliac sheath. 17 the outwards rotation of the replacement tooth trenches, particularly that of the lowerjaw. 18 the posterior extension of the premaxilla medially, and the associated development ofstrong interpremaxillary interdigitations. 19 the ontogenetic reduction in the roof of the premaxillary fossa. 20 the reduction of the maxilla. 21 the loss of maxillary teeth. 22 the loss of the inner dentary tooth row. 23 the enlarged cartilage pad between the palatine and maxilla. 24 the development of a large cartilage pad between the palatine and premaxilla. 25 the ontogenetic reduction of the lateral articular processes of the supraethmoid and theirfusion with the enlarged median supraethmoid process. 26 the restructuring of the lower pharyngeal into a fenestrated, dorsally convex, edentulousbone. 27 the fusion of upper pharyngeal tooth plates 4 and 5, and the reduction or loss of theassociated dentition. 28 the loss of pharyngobranchial 1 . 29 the elongation and anterior shift of pharyngobranchials 2 and 3. 30 the possession of micro-gillrakers. 31 the large, elaborate epi branchial organ. 32 the pronounced flexure in the parasphenoid. 33 the ontogenetic development of a bulbous ventral parasphenoid process. 34 the two broad regions of contact between the lateral ethmoid and orbitosphenoid. 35 the prominent, horizontal bulge at the orbitosphenoid-pterosphenoid joint. 36 the loss of the dorsal posttemporal fossa. 37 the elongate fontanelle extending midway into the supraethmoid. 38 the prominent ridge on the elongate anterodorsal process of the opercle. 39 the extension of the suprapreopercle over the anterodorsal portion of the opercle. 40 the reduced dermosphenotic. 41 the expansion of the dilatator fossa onto the frontal. 42 the attachment of the lateral section of the A 2 portion of the adductor mandibulae ontothe A w . 43 the relative reduction of the A 3 portion of the adductor mandibulae. 44 the enlargement of the A w portion of the adductor mandibulae into a large muscleextending dorsal of the edge of the angulo-articular. 45 the marked enlargement of the dilatator operculi. CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 327 46 the elongation of the intestinal tract. 47 the pronounced outpocketings of the terminal portion of the intestine. Within citharinids, two genera, Citharinus and Citharidium, are recognized at present. Asdescribed previously, the form of the ctenoid scales in Citharidium (48) appears to be uniqueamong characoids to this monotypic genus. Traditionally, Citharinus has been distinguished fromCitharidium on the basis of the former taxons having cycloid scales. However, such a scale formis plesiomorphous for characoids and thus cannot serve to define a monophyletic group. Theonly autapomorphous character for Citharinus found during this study is its lack of the parietalportion of the supraoccipital sensory canal (49). Such a loss, which appears to be derived forcharacoids, was previously noted by Daget (19626, p. 95). Daget has also dealt with the ecologyand aspects of the anatomy and taxonomy of both Citharinus and Citharidium (\962a & b). Family Distichodontidae As defined in this study the family Distichodontidae is both the most speciose and morpho-logically diverse of the families under consideration. Perhaps as a consequence of these factors,the Distichodontidae was previously subdivided into four subfamilies by Eigenmann (1909)and Regan (1911). More recently two subfamilies (Distichodontinae and Ichthyborinae) orfamilies (Distichodontidae and Ichthyboridae) have been recognized within this assemblage.However, as will be discussed in the Conclusions section, the results of this study have led tothe retention of only a single family, the Distichodontidae, for the genera previously partitionedamong several subfamilies or families. Despite this extensive intrafamilial variation, the Distichodontidae is not characterized by alarge series of synapomorphous characters. The derived characters supporting the hypothesizedmonophyletic nature of the family Distichodontidae are: 50 the distinctive ctenoid scales having the ctenii formed by a series of independentossifications. 51 the posterior process of the lateral ethmoid which extends posteriorly to contact theanteromedial edge of the orbitosphenoid. 52 the deeply bifurcate pelvic bone. 53 the mobility of the premaxilla on the supraethmoid. 54 the anterior shift and reduction or loss of the supraorbital. 55 the attachment of the A x portion of the adductor mandibulae to the maxilla (this attach-ment is secondarily lost in some genera, see p. 320). These apomorphous characters define an assemblage of genera that is, in turn, divisible intotwo monophyletic subgroups. One unit consists of the genus Xenocharax, and the other ofNannaethiops, Neolebias, Parodist ichodus, Distichodus, Nannocharax, Hemigrammocharax,Hemistichodus, Ichthyborus, Microstomatichthyoborus, Mesoborus, Eugnatichthys, Paraphago,Phago and Belonophago. In terms of overall body form, myology, osteology and dentition, Xenocharax is the leastderived member of the monophyletic unit formed by citharinids and distichodontids. This general-ized morphology is reflected in the omnivorous diet of this monotypic genus (see Daget, 1960,p. 39). Although characterized by a generalized morphological plan, the genus, nonetheless,possesses a series of apomorphous characters, some of which are unique to Xenocharax amongcharacoids examined. These adaptations include: 56 the posterodorsal shift of the longitudinal axis of the vertebrae of the pars sustentaculum. 57 the marked reduction in the angle between the axis of the pars sustentaculum and theaxis of the os suspensorium. 58 the subdivision of the suprapreopercle into two bony tubes. 59 the reduction in the branchiostegal number to three. 60 the increase to two inner dentary tooth rows. Further information on the anatomy, biology and distribution of this genus is provided byDaget (1960). 328 R. P. VARI The subunit of distichodontids formed by Nannaethiops, Neolebias, Paradistichodus, Dis-tichodus, Nannocharax, Hemigrammocharax, Hemistichodus, Ichthyborus, Microstomatichthyo-borus, Eugnatichthys, Paraphago, Phago and Belonophago has a series of synapomorphies involvingalterations to the pterotic and dermosphenotic and their associated sensory canals, together withadaptations of the neurocranium and opercle. The synapomorphous characters shared by thesegenera are : 61 the posterior expansion of the dermosphenotic over the primitively exposed lateralsurface of the pterotic. 62 the shift of the contact of the suprapreopercle to the dermosphenotic. 63 the elaboration of the plesiomorphously Y-shaped dermosphenotic sensory canal systeminto an H-shaped complex. 64 the decrease in the laterally exposed portion of the pterotic and the reduction of thepterotic sensory canal system to a simple tube. 65 the possession of some form of fenestrated opercle. 66 the reduction of the cranial fontanelle so that it barely extends anterior of the epiphysealbar. Two subunits of the assemblage defined by characters 61-66 can in turn be distinguished by theirless universal apomorphous characters. The first subunit is formed by the genera Nannaethiopsand Neolebias, while the second consists of Paradistichodus, Distichodus, Nannocharax, Hemi-grammocharax, Hemistichodus, Ichthyborus, Microstomatichthyoborus, Mesoborus, Eugnatichthys,Paraphago, Phago and Belonophago. The complex formed by the genera Nannaethiops and Neolebias (the latter in this sense isequivalent to Neolebias, Congocharax and Dundocharax of previous authors) can be defined bythe following derived characters: 67 the expansion of the suprapreopercle into a flat plate fitting the posteroventrally concavedermosphenotic. 68 the loss of the suprapreopercular sensory canal segment. 69 the marked secondary reduction or loss of the lateral ethmoid process extending betweenthe lateral ethmoid and orbitosphenoid. 70 the reduction or loss of the portion of the dermosphenotic sensory canal communicatingwith the suprapreopercular sensory canal. 71 the possession of a ectopterygoid tooth patch. 72 the loss of the sixth hypural. Among the distichodontid genera with several species, the complex formed by Nannaethiopsand Neolebias is undoubtedly the best understood at the alpha-level. In their revision of thesegenera, Poll & Gosse (1963) dealt with all of the then known species in addition to describingseveral new forms. More recently Matthes (1964) described a new species, Neolebias gracilis.In the same publication that author removed N. spilotaenia to the genus Congocharax along withC. olbrechtsi which previously had been included in Hemigrammocharax. Poll & Lambert (1964),in turn, described a new species, Congocharax gossei, and Poll (1967) erected the genus Dundo-charax for D. bidentatus which he described at the same time. Both Congocharax and Dundocharax,however, share the distinguishing characters of Neolebias and as will be discussed are placed intosynonymy of that genus. The cladogram of Fig. 48 shows the hypothesized interrelationships of Nannaethiops andNeolebias species based on evidence of this study. Characters uniting Neolebias and the monotypicgenus Nannaethiops into a monophyletic unit were discussed above. Apomorphous characterscommon to subunits of this assemblage are: (A) the reduction of the lateral line. (B) the reduction or loss of the posteroventral and posterodorsal segments of the dermo-sphenotic sensory canal segment. (C) the loss of one of the infraorbitals at the posterior margin of the orbit. (D) the shift of the remaining infraorbitals so as to retain a fully ossified orbital rim. (E) the total loss of the sensory canal systems of the dermosphenotic and pterotic. (F) the loss of the remaining infraorbital element at the rear of the orbit. CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE Neolebias 329 Fig. 48 Cladogram of the most parsimonious hypothesis of relationships in the unit formed by thegenera Nannaethiops and Neolebias. Synapomorphies A-H correspond to those of the text. (G) the loss of the dermosphenotic. (H) the distinctive sensory pore system of the head. Relationships of those species whose hypothesized phylogenetic position is based solely oninformation from the literature is indicated by dotted lines. Neolebias phillipei, as noted by Poll& Gosse (1963), appears to be closely related to N. trilineatus with which it shares an increasednumber of body stripes, a reduced circumpeduncular scale series and a low transverse scalecount. Neolebias olbrechtsi and N. gossei share with N. spilotaenia a distinctive cranial sensorypore pattern which is unique to these species among distichodontids (see Poll & Lambert, 19646,p. 407). Whether the former species also have N. spilotaenia 's distinctive gill arch modificationsand loss of infraorbitals 2 and 3 awaits further study. Neolebias gracilis of Matthes (1964)cannot be more closely assigned on the basis of literature information. However, it is difficult tovisualize how the characters of this species could drastically alter the phylogeny arrived at here.The most parsimonious phylogeny resulting from the described characters necessitates severalmodifications to the previous taxonomy of species placed in Neolebias as a result of this study. Neolebias bidentatus was originally placed by Poll (1967, p. 129) in the genus Dundocharaxwhich was described at the same time. Despite Poll's statement that 'Ce genre est voisin du genreHemigrammocharax . . .', the evidence now available shows it to belong to Neolebias as definedin this study. In addition to having the various characters autapomorphous for Neolebias amongdistichodontids, Dundocharax also lacks the multitude of apomorphous characters unitingHemigrammocharax to Nannocharax and Distichodus. Neolebias spilotaenia, N. gossei and N.olbrechtsi, in turn, were placed in Congocharax by Matthes (1964) and Poll & Lambert (1964)on the basis of their distinctive cranial sensory pore patterns. Although available evidence supports 330 R. P. VARI the hypothesis of the monophyletic nature of the unit formed by these three species, it alsoindicates that they are assignable to the genus Neolebias as defined herein. Although both Congo-charax and Dundocharax from monophyletic subunits of the Distichodontidae (the latter byvirtue of its monotypy), reference to the cladogram in Fig. 48 shows that the recognition of bothDundocharax (Neolebias bidentatus) and Congocharax (N. spilotaenia, N. olbrechtsi and TV.gossei) as separate genera would result in Neolebias (sensu stricto) being a non-monophyleticassemblage. This is a consequence of the fact that Neolebias is such a sense would not containall descendants of its hypothesized common ancestor. In light of this inconsistency with a basictaxonomic principle of this study, and in so far as a uniqueness criterion for the determination ofgeneric rank is arbitrary, both Dundocharax and Congocharax are placed as synonyms ofNeolebias. Neolebias in this broader sense now constitutes a monophyletic subunit of theDistichodontidae. A difference between the findings of this study and published observations should also benoted. Matthes in his diagnosis of the genus Congocharax (1964, p. 76) stated that it has the'Maxillaire non dente . . .', a statement repeated by Poll & Lambert (1964, p. 336). However,this comment is contrary to the observed presence of three or four maxillary teeth throughoutthe type series of Neolebias spilotaenia (the Congocharax spilotaenia of the above workers).Furthermore, it conflicts with Poll & Gosse's statement that this species is characterized by'Presence de dents a Tangle superieur de maxillaire.' Whether the reported absence of teeth inNeolebias gossei and N. olbrechtsi is correct awaits further study. [Since this paper has gone topress, I have had the opportunity to examine specimens of N. olbrechtsi. That species has twobicuspidate maxillary teeth and derived characters 1-72 and A-H for Neolebias.] The sister group to the unit formed by Nannaethiops and Neolebias is the multigenericassemblage consisting of Paradistichodus, Distichodus, Nannocharax, Hemigrammocharax,Hemistichodus, Ichthyborus, Microstomatichthyoborus, Mesoborus, Eugnatichthys, Paraphago,Phago and Belonophago. These genera share a series of synapomorphous jaw and suspensoriummodifications including: 73 the lengthening of the horizontal extent of the suspensorium with a resultant forwardshift of the articulation between the angulo-articular and quadrate. 74 the pronounced expansion of the premaxillary and dentary replacement tooth trenches. 75 the distinct horizontal shelf on the lateral surface of the quadrate and preopercle. 76 the loss of maxillary teeth. 77 the elongation of the teeth in the outer tooth row of each jaw and their pleurodontattachment to the anterior surface of the replacement tooth trench. 78 the possession of a distinct opercular fenestra. The subunit of the Distichodontidae defined by these characters is, in turn, divisible into twomonophyletic subunits. The first of these consists solely of the genus Paradistichodus, whereas thesecond contains Distichodus, Hemigrammocharax, Nannocharax, Hemistichodus, Ichthyborus,Microstomatichthyoborus, Mesoborus, Eugnatichthys, Paraphago, Phago and Belonophago. The genus Paradistichodus contains two species characterized by the following hypothesizedapomorphous characters : 79 the reduction in the number of hypurals to five. 80 the elongation of the supraethmoid. 81 the reduction in the number of epurals to one. 82 the reduction of the muscular portion of the lateral section of the A 2 portion of theadductor mandibulae. Daget (1958) has discussed the biology, and aspects of the anatomy of the two nominal Para-distichodus species, P. elegans from the Chad and Benue systems and P. dimidiatus from the Nigerand Gambia drainages. However, as discussed by Daget the differences between these nominalspecies are slight and may be a function of geographic variation. The assemblage consisting of Distichodus, Nannocharax, Hemigrammocharax, Hemistichodus,Ichthyborus, Microstomatichthyoborus, Mesoborus, Eugnatichthys, Paraphago, Phago and Belono-phago is characterized by the following hypothesized apomorphous characters: 83 the mobile articulation of the angulo-articular with the dentary. CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 331 84 the increased mobility of the upper jaw on the supraethmoid. 85 the increased attachment of the mesopterygoid to the neurocranium. 86 the increased envelopment of the palatine by the ectopterygoid and mesopterygoid.The two subunits definable within the group of genera sharing characters 83 to 86 are the speciose assemblage formed by Distichodus, Nannocharax and Hemigrammocharax, and themultigeneric unit consisting of Hemistichodus, Ichthyborus, Microstomatichthyoborus, Mesoborus,Eugnatichthys, Paraphago, Phago and Belonophago. The hypothesized monophyletic group consisting of Distichodus, Nannocharax andHemigrammocharax forms a very distinctive unit within distichodontids on the basis of a seriesof apomorphous characters, some of which are unique to this assemblage within characoids.These characters are : 87 the pronounced restructuring of the overall form of the dentary and the antero ventralreorientation of its longitudinal axis. 88 the reduction or loss of the sensory canal segment in the dentary. 89 the anterior restructuring of the angulo-articular into an anterodorsally or dorsally-directed plate. 90 the marked overlap of the dentary and angulo-articular. 91 the elongation of the outer row of premaxillary and dentary teeth. 92 the reduction or loss of the anteromedial process of the supraethmoid. 93 the dorsal shift of the insertion of the lateral section of the A 2 portion of the adductormandibulae. 94 the origin of the A w portion of the adductor mandibulae from the dorsal edge of thetendon of the A 2 and A 3 sections of the muscle, and the pronounced extension of theA w posterior of the edge of the angulo-articular. 95 the crossing at right angles of the ligamentum primordiale and the tendon of the A :portion of the adductor mandibulae. These characters are all either modifications of the jaws, or osteological and myologicalalterations correlated with the distinctive jaws and jaw action of these genera. Functionally,these alterations have resulted in a system permitting a degree of horizontal dentary motionthat is unique among characoids. Within the hypothesized monophyletic assemblage formed by Distichodus, Nannocharax andHemigrammocharax, a subunit consisting of Nannocharax and Hemigrammocharax is definableon the basis of the following synapomorphies : 96 the posteriorly-directed dentary processes flanking the dentary symphysis. 97 the loss of the inner premaxillary tooth row. 98 the loss of the sensory canal segment in the dentary. 99 the loss of the inner dentary tooth row. 100 the reduction or loss of the premaxillary articular fossa. 101 the vertical expansion of the posterior strut of the lateral ethmoid. 102 the horizontal expansion of the hyomandibula. 103 the loss of postcleithrum 1. 104 the development of anterior diverticulae of the anterior swimbladder chamber. 105 the restructuring of the ventral portion of the sphenotic spine into a posteroventrallysloping shelf. 106 the opening of the opercular fenestra to the dorsal margin of the bone. 107 the reduction of the metapterygoid-quadrate fenestra. Although both the assemblage formed by Distichodus, Nannocharax and Hemigrammocharax,and the unit consisting of Nannocharax and Hemigrammocharax are defined by a series ofapomorphous characters, the monophyly of the genera Distichodus, Hemigrammocharax andNannocharax is either refuted or brought into question by the results of this study. Previousclassifications utilized the larger size, higher dorsal fin-ray count and multiple rows of functionalpremaxillary and dentary teeth of Distichodus as the main characters distinguishing that genusfrom the unit formed by Nannocharax and Hemigrammocharax. However, in so far as allcitharinids and distichodontids are larger as adults than Nannocharax and Hemigrammocharax 332 R. P. VARI species, the larger size of Distichodus species relative to that of these genera appears to beplesiomorphous. Similarly, the high dorsal-fin ray count and inner row of premaxillary anddentary teeth are widespread among distichodontids (the former feature also occurs in citharinids).Thus both of these characters must be considered plesiomorphous for the group formed byDistichodus, Nannocharax and Hemigrammocharax. Consequently none of the characterspreviously used as distinguishing features of Distichodus relative to Nannocharax and Hemigram-mocharax is a valid basis for a hypothesis of the monophyly of Distichodus. Furthermore, noneof the apomorphous characters found during this study support such a hypothesis. Indeed theresults of this investigation indicate that as presently constituted Distichodus represents a gradelevel concept, with some Distichodus species more closely related to the unit formed by Nanno-charax and Hemigrammocharax than to their congeners. The characters refuting the hypothesisof the monophyly of Distichodus are: (A) the restructuring of the articular processes of the supraethmoid into pointed prong-likestructures in Distichodus lusosso, D. niloticus and D. fasciolatus. This approximatesto the hypothesized derived Nannocharax and Hemigrammocharax forms of thesestructures, but contrasts with the plesiomorphous flattened condition of the processes inDistichodus notospilus and D. brevipinnis. (B) the elongation of the supraethmoid in Distichodus lusosso, D. niloticus and D.fasciolatus. This feature is shared with Nannocharax and Hemigrammocharax butcontrasts with the plesiomorphous square supraethmoid in some Distichodus species. (C) the shift from the transversely elongate articular fossa on the rear of the pre maxillapresent in Distichodus notospilus and D. brevipinnis to a dorsally located pit in D.lusosso, D. niloticus and D. fasciolatus. The latter condition approximates to thederived articular fossa form of Nannocharax and Hemigrammocharax. (D) the ventral expansion of the sphenotic spine in Distichodus lusosso and D. niloticus, amodification carried further in Nannocharax and Hemigrammocharax. This conditioncontrasts with the plesiomorphous ventrally sharp-edged spine common to someDistichodus species. These characters and associated changes in neurocraninal form are congruent with thehypothesis that D. lusosso, D. niloticus and D. fasciolatus are more closely related to the unitformed by Nannocharax and Hemigrammocharax than to some of their congeners. It is thusconcluded that the genus Distichodus as presently defined is non-monophyletic. However, theexact distribution of these and other derived characters among the numerous nominal Distichodusspecies awaits further study as does a redefinition of Distichodus based on derived characters. As discussed previously Nannocharax and Hemmigrammocharax share a multitude ofapomorphous characters congruent with the hypothesized monophyly of the unit they formwithin distichodontids. However, the monophyly of each of these genera is open to question.Previous classificatory schemes differentiated these genera on the basis of the reduced lateral linein Hemigrammocharax, in contrast to the retention of the plesiomorphous complete lateral line inNannocharax. However, although it is most parsimonious to assume that a reduced lateral lineis derived within distichodontids, as discussed by Roberts (1967, p. 252) there is some doubt asto whether the reduced lateral line of the various Hemigrammocharax species results from commonancestry or multiple independent losses. Furthermore, the distribution of derived states of theinfraorbital series, fourth upper pharyngeal tooth plate and ossifications of the submaxillarycartilage are incongruent with the hypothesis of the monophyletic nature of both Nannocharaxand Hemigrammocharax as presently defined. A resolution of the question of the monophyletic nature of the genera Nannocharax andHemigrammocharax and of the relationships within the complex formed by Distichodus, Nanno-charax and Hemigrammocharax would necessitate a total revision of this speciose assemblage.Such an undertaking is beyond the aim of this study. Thus, until such a study is accomplished,these genera are tentatively retained as presently defined although the hypothesis of the mono-phyly of Distichodus is contraindicated and that of Nannocharax and Hemigrammocharax castin doubt. Further information on the ecology, anatomy and taxonomy of some Distichodus andNannocharax species can be found in Daget (1959, 1961). CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 333 The sister group to the assemblage formed by Distichodus, Nannocharax and Hemigrammo-charax consists of the genera Hemistichodus, Ichthyborus, Microstomatichthyoborus, Mesoborus,Eugnatichthys, Paraphago, Phago and Belonophago. These genera form a distinctive subunit ofdistichodontids sharing the following derived characters: 108 the marked reduction of the maxilla. 109 the loss of the medially-directed anterodorsal maxillary process. 110 the immovable articulation between the maxilla and premaxilla. 1 1 1 the prominent posterodorsal dentary process. 112 the elongation of the metapterygoid-quadrate fenestra and an increased contributionof the symplectic to its posterior border. 113 the markedly increased upper jaw mobility. 1 14 the medial shift of the position of the preopercular sensory canal. 115 the loss of the attachment of the A x portion of the adductor mandibulae to the maxilla. 1 16 the strongly developed teeth of the outer tooth row. The above adaptations are primarily associated with the functionally distinctive jaws character-istic of these genera. As noted earlier, the loss of the attachment of the A t portion of the adductormandibulae to the maxilla is considered an apomorphous secondary loss for this assemblage.Among other distichodontids such an attachment is advantageous in contributing to the greatermobility of the upper jaw. However, the restructuring of the jaws in the genera under discussionresults in a pronounced motion of the upper jaw without the necessity for an insertion of the A xon the maxilla. Indeed, in these genera the retention of such an attachment would be ineffectiveor of little advantage due to the drastically altered form of the maxilla and its immobile articula-tion with the premaxilla. Within the assemblage defined by apomorphies 108-116, two monophyletic subunits aredistinguishable on the basis of shared derived characters. These are the genus Hemistichodus andthe unit formed by Ichthyborus, Microstomatichthyoborus, Mesoborus, Eugnatichthys, Paraphago,Phago and Belonophago. The members of the genus Hemistichodus are distinguished by a series of jaw and dentalmodifications, most of which are unique among characoids examined. The apomorphies for thegenus are: 117 the greatly reduced maxilla which is totally excluded from the gape. 118 the pronounced development of the posterodorsal dentary ramus. 119 the great reduction and restructuring of the supraethmoid. 120 the modification of the premaxillary articular fossa into a rounded depression on thedorsal surface of the bone. 121 the loss of the inner tooth row on the dentary and premaxilla. 123 the lateral orientation of the replacement tooth trenches. Hemistichodus consists of three west African and Congo basin species which have a relativelysmall adult size. Within the genus, Hemistichodus mesmaekersi and H. lootensi are hypothesizedto form a monophyletic group on the basis of their apomorphous medially interrupted lateralline (see Daget, 1968, Fig. 1). These species, in turn, constitute the sister group to the thirdHemistichodus species, H. vaillanti. Daget (1968) has reviewed aspects of the anatomy, biologyand taxomony of the members of Hemistichodus. The sister group to Hemistichodus within the Distichodontidae is formed by the assemblageconsisting of Ichthyborus, Microstomatichthyoborus, Mesoborus, Eugnatichthys, Paraphago,Phago and Belonophago. These genera have a series of synapomorphous modifications of thejaws, neurocranium and dermal head bones including: 124 the loss of the posteroventral process of the dentary. 125 the reduction of the infraorbital series to four elements. 126 the interdigitating premaxillary joint or a further derived condition of such a symphysis. 127 the horizontal elongation of the sphenotic and the reorientation of the sphenotic spineinto a posteroventrally sloping or horizontal shelf having a reduced lateral extent. 128 the loss of the lateral ridge on the lateral commissure and on portions of the sphenoticand parasphenoid. 334 R. p. VARI 129 the reduced contribution of the prootic to the lip of the opening to the posteriormyodome. 130 the transverse ridge on the ventral surface of the frontal. 131 the posterior shift of the hyomandibular fossa and lateral commissure. 132 the slender, anteriorly concave hyomandibular. 133 the reduction of the cranial fontanelle to posterior to the epiphyseal bar. 134 the lateral and posterior expansion of the horizontal shelf on the lateral surface of thepreopercle. 135 the expansion of the origin of the adductor mandibulae onto the medial face of thehyomandibula and lateral surface of the sphenotic and pterotic. 136 the expansion of the origin of the levator arcus palatini onto the anterior surface of thesphenotic spine. These modifications, which are primarily related to the jaws and jaw action, result in a lowerjaw motion unique to these genera among characoids (see p. 271). Within this assemblage adichotomous sister group relationship is hypothesized between Ichthyborus (the Ichthyborus,Phagoborus and Gavialocharax of previous authors) and the multigeneric unit consisting ofMicrostomatichthyoborus, Mesoborus, Eugnatichthys, Paraphago, Phago and Belonophago. The genus Ichthyborus as herein defined is a distinctive assemblage of four species characterizedby the following synapomorphous characters : 137 the symphyseal fusion of the dentaries. 138 the enlargement of the anterior tooth cusp. 139 the possession of a median dentary tooth. 140 the form of the angulo-articular-dentary joint. 141 the posterodorsal expansion of infraorbital 4 and the congruent separation of thedermosphenotic from the orbital rim. 142 the marked median shift of the preopercular sensory canal segment in the verticalportion of the bone. 143 the loss of the ligamentous attachment of the palatine to the maxilla. 144 the insertion of the A x portion of the adductor mandibulae on the angulo-articular.Together these adaptations result in a distinctive subunit of distichodontids specialized for an ichthyovorous diet, although one subspecies of Ichthyborus besse is reported to be a fin eater(see Lek & Lek, 1978). The taxonomic concept of Ichthyborus in this work is, however, muchbroader than that of earlier workers. Figure 49 illustrates the hypothesized relationships of thefour species assigned to Ichthyborus in this study. The characters synapomorphous for Ichthyboruswere discussed above. Apomorphous characters common to subunits of this genus are: (A) the greater relative enlargement of the anterior tooth cusp. (B) the enlarged canine-like teeth at the front of each jaw. (C) the loss of the inner dentary tooth row. (D) the loss of the inner premaxillary tooth row. (E) the elongation of the jaws. Previous classifications placed Ichthyborus monodi and /. besse in the monotypic generaGavialocharax and Ichthyborus respectively, whereas /. ornatus and /. quadrilineatus were assignedto Phagoborus. However, in light of the phylogeny arrived at here, such a subdivision is untenablesince in such a system Phagoborus (the /. ornatus and I. quadrilineatus of this study) does notform a monophyletic unit. In order to resolve this inconsistency both Phagoborus and Gavialo-charax are synonymized with Ichthyborus. This results in Ichthyborus (sensu lato) forming amonophyletic multispecific subunit of distichodontids. In contrast, the alternative possibility,the erection of a new genus to contain /. quadrilineatus, fails to indicate the relationship of itssole species to other members of this complex and further subdivides an already greatly splitassemblage. Finally, a discrepancy between the findings of this study and published information should benoted. Pellegrin (1904) and Boulenger (1909) described Ichthyborus quadrilineatus (the Neoborusquadrilineatus of those authors) as having a single series of teeth in each jaw. However, in all /.quadrilineatus specimens examined an inner row of premaxillary teeth is also present. CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 335 The genera Microstomatichthyoborus, Mesoborus, Eugnatichthys, Paraphago, Phago andBelonophago are hypothesized as forming a monophyletic unit on the basis of their commonpossession of the following derived characters: 145 the enlargement of the posterior tooth cusp. 146 the possession of an immobile interdigitating joint at the rear of the dentary symphysis. 147 the anterior and posterior expansion of the third infraorbital. 148 the form of the angulo-articular-dentary articulation. 149 the loss of the supraorbital. 150 the reduction of the anteromedial supraethmoid process. 151 the possession of a posterodorsal preopercular flange. C Fig. 49 -137-144 Cladogram of the most parsimonious hypothesis of relationships in the genus Ichthyborus.Synapomorphies A-E correspond to those of the text Within the subunit of distichodontids defined by apomorphous characters 145-151, a dichotomyis hypothesized between Microstomatichthyoborus and the group formed by Mesoborus,Eugnatichthys, Paraphago, Phago and Belonophago. However, whereas the latter genera share aseries of apomorphous characters, no derived feature unique to Microstomatichthyoborus inthe Distichodontidae has been found in this study. Nonetheless, because of the lack of evidencecontraindicating the monophyly of the unit formed by the two nominal Microstomatichthyoborusspecies (bashforddeani and katangae), the genus is retained for the present. The genera Mesoborus, Eugnatichthys, Paraphago, Phago and Belonophago, in contrast, sharethe following apomorphous characters: 152 the reorientation of the sphenotic spine into an horizontal shelf. 153 the lateral reduction of the sphenotic spine so as to barely reach laterally to the frontal. 154 the loss of the cartilaginous rod joining the palatine to th0 .maxilla. 155 the pronounced reduction of the laterally exposed portion of the pterotic and ashortening of the pterotic sensory canal. 156 the elongation of the pterosphenoid and orbitosphenoid. 157 the ventral shift of the attachment of the gill arches to the parasphenoid. 158 the pronounced reduction of the cranial fontanelle. 159 the presence of a fossa on the rear of the hyomandibula to receive the dorsal tip of thepreopercle. Characters 152-158 distinguish a generic assemblage which can in turn be divided dicho-tomously. One subunit consists of the genus Mesoborus, whereas the other is formed by the generaEugnatichthys, Paraphago, Phago and Belonophago. 336 R. P. VARI Mesoborus is a distinctive genus whose single contained species, M. crocodilus, is a voraciouspredator (Matthes, 1964, p. 65). This life style is reflected in the following autapomor-phousmodifications: 160 the ontogenetic loss of the anterior tooth cusp resulting in a nearly unicuspidatedentition. 161 the enlarged second to fourth dentary teeth. 162 the development of the anterior premaxillary teeth into canines. 163 the reduction of the second to fourth premaxillary teeth which arise from a distinctlyconcave region of the premaxilla. The sister group to Mesoborus among distichodontids is formed by the genera Eugnatichthys,Paraphago, Phago and Belonophago. This assemblage is characterized by the following apo-morphies: 164 the transversely thickened and horizontally shortened angulo-articular. 165 the posteroventral recontouring of the maxilla into a rounded knob. 166 the development of a groove on the lateral surface of the posterodorsal dentary ramus. 167 the marked reduction of the anteromedial supraethmoid process. 168 the expanded, laterally-orientated supraethmoid articular processes. 169 the restructuring of the premaxillary articular fossa into a laterally directed pit. 170 the laterally reduced sphenotic spine which falls short of the edge of the frontal. 171 the reduction of the anterior sphenotic process capping the transverse ridge of thefrontal. 172 the pronounced dorsal process of the hyomandibula. 173 the possession of a ventromedial parasphenoid ridge. 174 the reduction of the vertical extent of the levator arcus palatini and its attachment tothe hyomandibula via an aponeurosis. Most of these characters are either changes in the form of the jaws or alterations in theirrelationships to each other, the neurocranium and the suspensorium. These adaptations resultin a close meshing of the upper and lower jaws during closure of the mouth. This tight fit togetherwith the pronounced gape characteristic of these genera and their enlarged adductor mandibulaemuscles results in a system well adapted for the fin-nipping habits previously reported for Phago,Belonophago and Eugnatichthys (see Matthes, 1961; Gosse, 1963; Burchard, 1968) and foundin Paraphago during this study. This assemblage of genera can, in turn, be dichotomously divided into two monophyleticsubunits. These are the genus Eugnatichthys and the unit consisting of Paraphago, Phago andBelonophago. Eugnatichthys is a distinctive genus of distichodontids characterized by the following auta-pomorphous characters: 175 the massive development of the premaxilla and dentary. 176 the transverse expansion of the maxilla. 177 the transversely expanded angulo-articular. 178 the subdivision of the A 3 portion of the adductor mandibulae muscle. 179 the horizontal elongation of the sphenotic, with an associated shift posteriorly of thelateral commissure and hyomandibular fossa. 180 the pronounced development of the median parasphenoid ridge into a knife-likeprocess. 181 the reduction of the dorsal posttemporal fossa. Eugnatichthys is composed of only two species (eetveldii and macroterolepis} but is one of themost distinctive genera among distichodontids as a consequence of its relatively massive jaws.These adaptations of the jaws and associated osteological systems, together with the pronounceddevelopment of the adductor mandibulae muscles, permit these species to bite off relativelythicker fin segments than can any other fin-eaters examined. The hypothesized sister group to Eugnatichthys is formed by the unit consisting of Paraphago,Phago and Belonophago. This assemblage is characterized by the following hypothesized apo-morphous characters: CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 337 182 the reduction or loss of infraorbital 4. 183 the expansion ventrally of the dermosphenotic. 184 the contact of the posteroventral border of the pterosphenoid with the ascendingprocess of the parasphenoid. 185 the elongation of the jaws. 186 the loss of the anterior sphenotic process plesiomorphously capping the transverseridge of the frontal. It should be noted, however, that because Paraphago is known only from its syntypes, it wasnot possible to study the genus myologically, or to analyse those internal osteological charactersnot amenable to examination by radiographs. It is thus possible that some of the characterslisted below as synapomorphies for Phago and Belonophago are shared with Paraphago. Althoughno characters autapomorphous for Paraphago within distichodontids were found during thisstudy, the genus is, nonetheless, monophyletic by virtue of its monotypy. The remaining distichodontid genera, Phago and Belonophago, share the following hypothesizedsynapomorphies : 187 the marked expansion of the supraethmoid articular processes into rounded, laterally-directed structures. 188 the extensive horizontal elongation of the symplectic, metapterygoid and meta-pterygoid-quadrate fenestra. 189 the loss of infraorbital 4. 190 the pronounced ventral expansion of the dermosphenotic. 191 the pronounced dorsal expansion of infraorbital 3. 192 the heavy bony scales having a prominent bump over the scale focus. 193 the single epural. 194 the very wide contact of the posteroventral margin of the pterosphenoid with theascending process of the parasphenoid. 195 the ventral expansion of the fused postcleithra 2 and 3. 196 the expansion of the origin of the levator arcus palatini onto the ventral surface of thefrontal. Phago and Belonophago are, in turn, each characterized by several autapomorphous characters.Derived features of Phago are : 197 the thickened, vertically elongate scales. 198 the anteroventrally curved premaxilla that overlaps the anterior end of the dentaries.Presently four nominal species of Phago (boulengeri, inter medius, loricatus and maculatus} occur in the literature. However, P. maculatus of the Niger drainage is questionably distinct fromP. loricatus of the same system. Belonophago is a very distinctive genus having the following autapomorphies: 199 the marked elongation of the jaws. 200 the expansion of the pterosphenoid so as to form the entire anterior surface of thebraincase. 201 the median contact between the pterosphenoid and parasphenoid. 202 the extreme elongation of the metapterygoid and symplectic. 203 the loss of the sensory canal system in the dermosphenotic. 204 the loss of the sensory canal system in infraorbital 3. 205 the posteriorly-directed spinous processes on the scales. 206 the secondary loss of the transverse ridge on the ventral surface of the frontal. The two nominal Belonophago species (tinanti and hutsebouti) are characterized by a markedlyelongate, cylindriform shape (see Poll, 1957, Fig. 142). The fin-nipping habits of this genus werereported on by Matthes (1961, p. 78) and confirmed in this study by stomach content analyses. Convergent characters The hypothesis of relationships presented above is the most parsimonious derivable fromavailable information on character distribution and polarity in the systems analysed amongcitharinids and distichodontids. However, as might be expected in such a large diverse assemblage, 338 R. P. VARI there occur a number of hypothesized apomorphous characters whose distribution is incongruentwith that of the overall most parsimonious hypothesis of relationships. The majority of theseincongruities are loss characters. Although loss characters provide useful information for aphylogenetic reconstruction, they can sometimes be misleading in so far as the non-homologyof losses can be difficult to ascertain. Apomorphous loss characters which have a distributionincongruent with that of a majority of the derived characters among citharinids and disticho-dontids are: (A) the loss of the maxillary teeth in citharinids and all distichodontids other thanXenocharax, Nannaethiops and Neolebias. (B) the loss of the inner dentary tooth row in citharinids, Hemistichodus, some Ichthyborusspecies and the unit formed of Nannocharax and Hemigrammocharax. (C) the loss of the inner premaxillary tooth row in Hemistichodus, some Ichthyborusspecies and the unit consisting of Nannocharax and Hemigrammocharax. (D) the loss of the sixth hypural in Paradistichodus and the unit formed by Neolebias andNannaethiops. (E) the loss of one epural in Paradistichodus and the group consisting of Phago andBelonophago (F) the loss of the cartilaginous connection between the palatine and maxilla in Ichthyborusand the assemblage containing Mesoborus, Eugnatichthys, Paraphago, Phago andBelonophago. (G) the reduction of the anteromedian supraethmoid process in the group formed byDistichodus, Nannocharax and Hemigrammocharax, and the unit consisting ofMicrostomatichthyoborus, Mesoborus, Eugnatichthys, Paraphago, Phago and Belono-phago. (H) the loss of the dermosphenotic sensory canal segment in some Neolebias species and the genus Belonophago. (I) the reduction of the lateral line in Neolebias and Hemigrammocharax.(J) the reduction of the maxilla in citharinids and the distichodontid genera Hemistichodus, Ichthyborus, Microstomatichthyoborus, Mesoborus, Eugnatichthys, Paraphago, Phago and Belonophago. Apomorphous gain characters evidently acquired independently several times in the assemblageformed by the Citharinidae and Distichodontidae are: (A) the elongation of the jaws in some Ichthyborus species and the assemblage formed byParaphago, Phago and Belonophago. (B) the presence of a second inner dentary tooth row in Xenocharax and some Neolebiastrilineatus specimens. (C) the elongation of the supraethmoid in Paradistichodus and the unit consisting ofNannocharax, Hemigrammocharax and some Distichodus species. (D) the interpremaxillary interdigitations of citharinids and the group formed byIchthyborus, Microstomatichthyoborus, Mesoborus, Eugnatichthys, Paraphago, Phagoand Belonophago. In addition to the characters listed above there is also a series of apomorphies which althoughseemingly convergent within citharinids and distichodontids can, nonetheless, be shown to benon-homologous. Foremost among these is the loss of infraorbitals 4 and 5 in some Neolebiasspecies, some Nannocharax species and the subunit of distichodontids formed by Ichthyborus,Microstomatichthyoborus, Mesoborus, Eugnatichthys, Paraphago, Phago and Belonophago. Asdiscussed earlier the loss of these bones in each of these groups is achieved by an independentnon-homologous method. Similarly, the mode of reduction or loss of the metapterygoid-quadratefenestra differs between Neolebias spilotaenia and the unit formed by Nannocharax and Hemi-grammocharax. In the former the opening is eliminated by an expansion of the symplectic, whereasin the latter genera the fenestra is reduced or lost as a consequence of the approximation of thesymplectic and metapterygoid. Similarly, the medially interrupted lateral line is Hemistichodusdiffers from the reduced lateral line of Neolebias and Hemigrammocharax. In the latter genera, CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 339 the lateral line is lacking both medially and posteriorly with this reduction limited to the posteriorpart of the body in some Hemigrammocharax species (see H. angolensis, Poll, 1967, Fig. 51). As noted earlier, the canine dentition of the lower jaws of Mesoboms and some Ichthyborusspecies differs in which teeth are enlarged. Although both of these taxa have the anterior teethof the premaxilla enlarged, these canines are non-homologous. In Mesoboms the enlarged anteriorpremaxillary teeth are a consequence of the great expansion of the posterior tooth cusp. InIchthyborus, in contrast, the canines are formed by an enlarged anterior cusp. Finally, it should be noted that the differences between the reduced maxilla of citharinids andsome distichodontids (loss character J) are such as to cast doubt in the homology of thesereductions. Similarly, the interpremaxillary interdigitations occurring in citharinids and a subunitof distichodontids (gain character D) are rather different and may have arisen independently. Thus many of the seemingly convergent characters are, on closer examination, found to benon-homologous. Even in those cases where the homology of the convergencies is not refuted,the overall distribution of apomorphous characters is such that any alterations made to theproposed phylogeny, in order to resolve some or all of these evident convergencies, results in aless parsimonious theory of interrelationships. Conclusions The translation of the proposed phylogeny into a classification has necessitated several majorchanges in the previous generic and suprageneric taxonomy of the genera herein assigned to thefamilies Citharinidae and Distichodontidae. Most previous classifications (Boulenger, 1909;Monod, 1950; Greenwood et al., 1966) recognize three families or subfamilies for this group ofgenera. Although the taxonomic level applied to any group of organisms is arbitrary, the familiallevel ranking of Greenwood et al., which is most widely used in the modern literature, is retained. The family Citharinidae of Greenwood et al. (1966) remains unchanged in so far as it was foundto represent a monophyletic unit. In contrast, the previous concepts of the Distichodontidae (orsubfamily Distichodontinae) included the genera Xenocharax, Nannaethiops, Neolebias (theNeolebias, Congocharax and Dundocharax of previous authors), Paradistichodus, Distichodus,Nannocharax and Hemigrammocharax in the family (or subfamily). Reference to the proposedphylogeny shows, however, that such a classification results in the family representing a gradelevel assemblage. This gradal taxon forms a series of sister groups to a unit composed ofHemistichodus, Ichthyborus (the Ichthyborus, Phagoborus and Gavialocharax of previous authors),Microstomatichthyoborus, Mesoboms, Eugnatichthys, Paraphago, Phago and Belonophago. Thislatter assemblage constitutes the family Ichthyboridae or subfamily Ichthyborinae of earlierclassifications. In light of the proposed phylogeny we can see that under previous classifications,some distichodontids would be more closely related to ichthyborids than to members of their ownfamily. However, the retention of a gradistic, non-monophyletic taxon is untenable under thesystematic procedures adopted as a basis for this study. Consequently, the family Ichthyboridaeof Greenwood et al. (1966) (the Ichthyborinae of various authors) is sunk into the familyDistichodontidae. The family Distichodontidae in this broader sense now forms a monophyleticgroup within characoids. As discussed previously, the genera Congocharax and Dundocharax are placed as synonyms ofNeolebias in order to resolve the previously non-monophyletic nature of Neolebias. The generaPhagoborus and Gavialocharax, in turn are synonymized into Ichthyborus as a consequence ofthe previous non-monophyly of Phagoborus. Finally, although the monophyly of Distichodus,Nannocharax and Hemigrammocharax is refuted or cast into doubt by the results of this study,these taxa are tentatively retained until such time as the subunit they form in the Distichodontidaecan be studied in depth. To summarize, the proposed classification of these families is as follows :Family Citharinidae Genus Citharinus Cuvier, 1817Genus Citharidium Boulenger, 1902 340 R. P. VARI Family Distichodontidae Genus Xenocharax Giinther, 1867 Genus Nannaethiops Giinther, 1871 Genus Neolebias Steindachner, 1894 Genus Paradistichodus Pellegrin, 1922 Genus Distichodus Miiller and Troschel, 1845 Genus Nannocharax Giinther 1867 Genus Hemigrammocharax Pellegrin, 1922 Genus Hemistichodus Pellegrin, 1900 Genus Ichthyborus Giinther, 1864 Genus Microstomatichthyoborus Nichols and Griscom, 1917 Genus Mesoborus Pellegrin, 1900 Genus Eugnatichthys Boulenger, 1898 Genus Paraphago Boulenger, 1 899 Genus Phago Giinther, 1865 Genus Belonophago Giltay, 1929 The question of the relationship of the unit formed by citharinids and distichodontids to othercharacoids has not been resolved within this study. Various characters, such as the possessionof a suprapreopercle, the lack of an interdigitating symphyseal dentary hinge and the anteriorshift of the olfactory lobe, occur in groups outside of these families. However, in most casesthese outgroups can be shown to be part of larger assemblages whose other members lack theapomorphous character in question. The characoid outgroup that has the greatest number ofhypothesized apomorphous characters similar to those of, or occurring within, the unit formedby citharinids and distichodontids, is the Neotropical family Parodontidae. These bottom-dwelling fish, whose sister group is presently undetermined, have an anteriorly trifurcate supraeth-moid articulating with the premaxillary articular fossae of the posteroventrally shifted upper jaw.Furthermore, parodontids have a slight anterior shift of the olfactory lobes and a distichodontidtype of contact between the lateral ethmoid and orbitosphenoid. Such characters in isolationplace parodontids close to the distichodontid genus Nannocharax. However, an overall analysisof parodontid anatomy reveals a series of inconsistencies with such an hypothesis. The Paro-dontidae lack a series of the synpapomorphies defining the unit formed by citharinids anddistichodontids including: the modifications of the pars sustentaculum of the Weberian apparatus,the fusion of hypurals 1 and 2, the bicuspidate tooth form, the fusion of postcleithra 2 and 3, theseparate suprapreopercle, the ovoid third posttemporal fossa bordered by the epioccipital andexoccipitals and the bifurcate pelvic bone. Furthermore, parodontids lack most of the numeroussynapomorphies for distichodontids and for subunits of the Distichodontidae that includeNannocharax. Because of the absence of these characters in parodontids and because of otherincongruities, it is impossible either to place the Parodontidae as part of a unit formed by theCitharinidae and Distichodontidae within characoids or to consider them as a sister group to thatunit. A resolution of this problem posed by the seemingly independent acquisition of variousapomorphous characters in parodontids and certain subunits of citharinids and distichodontidsawaits a better understanding of characoid interrelationships. Comparisons with previous classifications As noted above, the classification arrived at in this study differs from those of Boulenger (1909)and Greenwood et al. (1966) which recognized two families or subfamilies within the groupforming the family Distichodontidae of this study. Whereas such a division was the mostcommonly accepted classificatory scheme for the last three-quarters of a century, some workersdivided citharinids and distichodontids along different lines. Regan (1911, pp. 21-23) recognizedfive subfamilies, one of which, his Xenocharacinae, was non-monophyletic according to thephylogeny proposed in this work. Eigenmann (1909, pp. 253-255) also recognized five subfamilies,but with different limits. Although he did not specifically list the genera assigned to each of thetaxa, Eigenmann's key shows both his Neolebiinae and Ichthyborinae to be non-monophyletic, CLASSIFICATION OF CITHARINIDAE AND DISTICHODONTIDAE 341 even allowing for the fewer species and genera described at that time. Subsequently, Gregory &Conrad (1938, p. 350) expanded the subfamily Citharininae to include Citharinus, Citharidium,Nannaethiops, Neolebias, Xenocharax and Hemistichodus. Their Distichodontinae, in turn, wascomposed of the genera Distichodus, Nannocharax, Ichthyborus, Mesoborus, Phagoborus,Eugnatichthys, Paraphago and Phago. However, a comparison of the limits of these taxa with thephylogeny here proposed shows that neither of Gregory & Conrad's subfamilies represents amonophyletic unit. That is, neither contains all the descendants of its hypothesized commonancestor. Monod (1950, p. 58) recognized three subfamilies, Citharininae, Distichodontinae andIchthyborinae, within the group under discussion. However, his definition of the Distichodontinae(characterized by the 'Articulaire et dentaire articules par chevauchement lateral . . .' - theDistichodus form of lower jaw) excludes Neolebias, Nannaethiops, Xenocharax and Paradistichodusfrom that subfamily. Furthermore, these genera are similarly excluded from the Citharininae andIchthyborinae under Monod's definition of those subfamilies. Finally, Poll (1973, Fig. 1) listshis Citharininae as consisting of Citharinus, Citharidium, Xenocharax, Nannaethiops, Neolebias,Dundocharax, Paradistichodus, Distichodus, Nannocharax and Hemigrammocharax (on p. 114of his paper he stated that there are eleven citharinid genera. The missing genus of his Fig. 1appears to be Congocharax). The expansion of the family Citharinidae by this group of nominaldistichodontid genera, although resolving the non-monophyly of the Distichodontidae (sensuGreenwood et al., 1966), as a consequence of the elimination of the taxon, simultaneously convertsthe previously monophyletic Citharinidae into a gradal non-monophyletic group. Comments on the African Characidae In the course of outgroup comparisons involved in this study of the Citharinidae and Dis-tichodontidae, several characters of relevance to an understanding of the hypothesis of themonophyly of the African Characidae and to relationships within African characids were found.As noted by Roberts (1969, p. 441) the shape of the upper jaw and dentition is distinctive forAfrican characids among characoids. Furthermore, all African characids examined during thisstudy, with the exception of Lepidarchus, have a small third posttemporal fossa totally containedwithin the epioccipital. The possession of this apomorphous character together with the uniquejaw and dental modifications described above is consistent with the hypothesis that the AfricanCharacidae forms a monophyletic subunit of characoids. Thus on the basis of available information, African characoids can be assigned to three mono-phyletic groups: the unit formed by the Citharinidae and Distichodontidae; the assemblageformed by the members of the African Characidae; and the monotypic family Hepsetidae.However, relationships of these groups to each other and to Neotropical characoids are presentlyundetermined. Several other characters are of relevance for an understanding of the relationships within theAfrican Characidae and for questions on the validity of the presently recognized generic andsuprageneric taxa in this group. In the course of the discussion on the morphology of the anteriororbital region, it was noted that a bony tube surrounding the olfactory tract and bulb wasdescribed by Starks (1926, p. 167) for Alestes liebrechstii and A. grandisquamis. More recentlyRoberts (1969, p. 441) also noted this orbitosphenoid process in Alestes baremose, A. imberi, A.marcolepidotus, Bryconaethiops and Hydrocynus, and it has also been found in Alestes dentexand A. macrophthalmus during this study. This bony tube, which is lacking in all other Africancharacids examined, is hypothesized as being apomorphous for these taxa among characoidson the basis of ontogenetic and outgroup comparisons. Those species with an orbitosphenoidtube also have the premaxillae joined by interpremaxillary interdigitations. As discussed earlier,both the broadened contact of the premaxillae anterior to the supraethmoid spine, and theassociated symphyseal interdigitations are considered apomorphous and thus indicative of themonophyletic nature of the assemblage formed by the taxa possessing them. Congruent withthese apomorphic modifications of the premaxillae and orbitosphenoid is the forward shift ofthe olfactory bulb in Hydrocynus, Bryconaethiops and various Alestes species (imberi, dentex,liebrechstii, macrophthalmus, macrolepidotus, nurse, rhodopleura and lateralis; the condition of 342 R. P. VARI the orbitosphenoid and premaxillae is unknown for the last three species). Such a derived anteriorshift of the olfactory bulb is lacking among the other Alestes species and African characid generaexamined. On the basis of these characters (the orbitosphenoid tube, the anterior shift of theolfactory bulb and the interdigitation of the premaxillae) it appears that the above Alestes speciesand the genera Bryconaethiops and Hydrocynus form a monophyletic subunit of the AfricanCharacidae. Further studies are required to determine the exact distribution of the above derived osteologyand neurological characters within African characids. Nonetheless, the available evidencecontraindicates the inherent hypotheses of the monophyly of the genus Alestes and the subfamilyAlestiinae as now defined. The genus Alestes, in its present sense, does not form a monophyleticunit in so far as the distribution of apomorphous characters indicates that some of its membersare more closely related to species of the genera Bryconaethiops and Hydrocynus than to theremaining Alestes species. A redefinition of Alestes as a monophyletic unit must, however, awaita detailed anatomical study of African characids and a phylogenetic analysis based on informationfrom derived characters, both those discussed previously and others. Roberts (1969, p. 442) divided the African Characidae into two subfamilies. These were theHydrocyninae limited to the genus Hydrocynus and the Alestiinae for all other African characids.However, although the Hydrocyninae of such a classificatory scheme represents a monophyleticunit, the Alestiinae of that system is an unnatural grouping. As detailed above, the generaHydrocynus and Bryconaethiops share a series of derived characters and form a monophyleticassemblage with some Alestes species. Consequently, a subdivision of African characids intotwo subfamilies along the lines proposed by Roberts results in some members of the subfamilyAlestiinae (Bryconaethiops and various Alestes species) being more closely related to members ofanother subfamily (Hydrocyninae) than they are to the remaining taxa within their own subfamily.Thus the Alestiinae of Roberts must be considered a gradal non-monophyletic assemblage.Although the exact distribution of the derived characters discussed above is undetermined, theevidence is sufficient to indicate that the Hydrocyninae of Roberts (1969) should be sunk into theAlestiinae in order to resolve the present non-monophyly of the latter subfamily. The Alestiinaein this broader sense forms an evidently monophyletic assemblage within the Characoidea. Acknowledgements A number of individuals and institutions have been instrumental to the completion of this study. I thank Dr Donn E. Rosen for directing my interests towards questions of characoid inter-relationships. Dr P. Humphry Greenwood and Mr Gordon J. Howes contributed significantlyto this study by their informative comments on characoid morphology and interrelationships,together with helpful criticisms of earlier drafts of the manuscript. Mr Howes and Mrs MargaretClarke were most helpful in locating specimens, preparing radiographs and other assistanceduring this study. The majority of the research associated with this project, together with the synthesis of theresults, was undertaken in the Department of Zoology, British Museum (Natural History).Research at that institution was supported by a NATO Postdoctoral Fellowship to the author.Supplemental studies were undertaken at the American Museum of Natural History and the finaldraft of the paper was prepared at the Smithsonian Institution, Washington D.C. under aSmithsonian Postdoctoral Fellowship. Drs D. F. 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A descriptive synonymy of the striated muscles of the teleostei. Proc. Acad. nat. Sci. Phi lad. 125:225-317. Manuscript submitted for publication 20 July 1978 British Museum (Natural History)Publication on fishes The Cicblid fishes of Lake Victoria, East Africa. The biology and evolution of a species flock. P. H. Greenwood. Bull. British Museum (Natural History) Zool. Suppl. No. 6, 1974 vi + 134 pp, 1 coloured plate, 77 text figures, 4to, (paper) 6.00 (boards) 8.25 The feeding mechanisms of a deep sea fish, Chautiodus sloani Schneider. V. V. Tchernavin 1953, viii-f 101 pp, 10 plates, 36 text figures, 4to paper, 3.85 Forty drawings of fishes, made by the artists who accompanied Captain James Cook. P. J. P. Whitehead 1968, xxvii pp, 36 collotype colour plates, demy folio boards, 55.00 The Clupeoid fishes described by Lacepede, Cuvier andValenciennes. P. J. P. Whitehead Bull. British Museum (Natural History) Zool. Suppl. No. 2, 1967,180 pp, 11 plates, 15 text figures, 4to paper, 7.00 The Clupeoid fishes of the Guianas. P. J. P. Whitehead Bull. British Museum (Natural History) Zool. Suppl. No. 5, 1973, 227 pp, 72 text figures, 6 tables, 4to paper, 13.50 Lists are available free on request to : Publications Sales British Museum (Natural History) Cromwell Road London SW7 5BD Standing orders placed by educational institutions earn a discountof 10% off our published price. Titles to be published in Volume 36 A guide to the species of the genus Aspidisca.By Irene C. H. Wu & C. R. Curds. The Hemiuroidea : terminology, systematics and evolution.By D. I. Gibson & R. A. Bray. Notes on the anatomy of Macrochirichthys macrochirusValenciennes, 1844, with comments on the Cultrinae (Pisces,Cyprinidae). By G. J. Howes. Miscellanea Anatomy, relationships and classification of the familiesCitharinidae and Distichodontidae (Pisces, Characoidea),By R. P. Vari. Printed by Henry Ling Ltd, Dorchester