UNIVERSITY OF ILLINOIS LIBRARY AT URBANA-CHAMPAIGN BIOLOGY APR 0 9 1992 590.5 FI n.s. BIX nc.ki -^ VNA Zoology NEW SERIES, NO. 61 Hoplomyzon sexpapilostoma, a New Species of Venezuelan Catfish (Pisces: Aspredinidae), with Comments on the Hoplomyzontini Donald C. Taphorn Crispulo Marrero JN iovember 30, 1990 Publication 1417 PUBLISHED BY FIELD MUSEUM OF NATURAL HISTORY Information for Contributors to Fieldiana General: Fieldiana is primarily a journal for Field Museum staff members and research associates, although manuscripts from nonaffiliated authors may be considered as space permits. The Journal carries a page charge of $65.00 per printed page or fraction thereof. Payment of at least 50% of page charges qualifies a paper for expedited processing, which reduces the publication time. 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Changes in page proofs (as opposed to corrections) are very expensive. Author-generated changes in page proofs can only be made if the author agrees in advance to pay for them. THIS PUBLICATION IS PRINTED ON ACID-FREE PAPER. [ FIELDIANA Zoology NEW SERIES, NO. 61 Hoplomyzon sexpapilostoma, a New Species of Venezuelan Catfish (Pisces: Aspredinidae), with Comments on the Hoplomyzontini Donald C. Taphorn Crispulo Marrero Museo de Ciencias Naturales de Guanare Universidad National Experimental de los LLanos Occidentales Ezequiel Zamora, Programa de Recursos Naturales Renovables Guanare, Portuguesa Venezuela 3310 Accepted October 17, 1989 Published November 30, 1990 Publication 1417 PUBLISHED BY FIELD MUSEUM OF NATURAL HISTORY © 1 990 Field Museum of Natural History ISSN 0015-0754 PRINTED IN THE UNITED STATES OF AMERICA Table of Contents List of Tables Abstract 1 1 . Comparison of mensural characters for Resumen 1 type specimens of Hoplomyzon and para- Introduction 1 types of H. sexpapilostoma 2 Methods 2 2. Character comparison of the tribes Hoplo- Hoplomyzon Myers, 1 942 2 myzontini and Bunocephalini 9 Key to Species of Hoplomyzon Myers .... 3 Hoplomyzon sexpapilostoma, new species . . 4 Status of the Hoplomyzontini 8 Acknowledgments 9 Literature Cited 9 List of Illustrations 1 . Color patterns, caudal fin blotch, and ventral view of anterior of Hoplomyzon sexpapilostoma 3 2. Views of pectoral and pelvic girdles of Hop- lomyzon sexpapilostoma, Ernstichthys anduzei, Bunocephalus amaurus, and Xi- liphius cf. lepturus 4 3. Ventral elements of Hoplomyzon sexpa- pilostoma and Ernstichthys anduzei 6 4. Caudal vertebrae and caudal skeletons of Hoplomyzon sexpapilostoma, Bunocepha- lus amaurus, and Xiliphius cf. lepturus ... 7 in Hoplomyzon sexpapilostoma, a New Species of Venezuelan Catfish (Pisces: Aspredinidae), with Comments on the Hoplomyzontini Abstract A new species of aspredinid catfish belonging to the tribe Hoplomyzontini was collected as part of a general inventory of the fishes of the Apure River Drainage (Orinoco Basin) of western Venezuela. Hoplomyzon sexpapilostoma, new species, is dis- tinguished from all known aspredinids by the fol- lowing combination of characters: ( 1 ) The anterior border of the snout is slightly emarginate, vs. deep- ly emarginate in H. papillatus or straight in H. atrizona. (2) There are no barbels at the rictus of the mouth as in H. atrizona. (3) They have four papillae on the upper lip, instead of three as in H. papillatus (or five, including the rictal pair). (4) Dorsal rays i5 vs. i6 in H. atrizona, i3i in H. papil- latus. (5) Maxillary barbels long but not surpassing the pectoral fin origins (18.8% SL). (6) The ossified lateral line tubules are arranged in a zigzag pattern to a point beneath the center of the dorsal fin base, but are straight from there back to the caudal pe- duncle (in H. papillatus the zigzag pattern contin- ues to the caudal peduncle, and in H. atrizona it is completely straight). (7) The second pelvic ray is slightly longer than the rest (it forms a filament in H. papillatus and is short in H. atrizona). (8) The dorsal and anal fins are united to the dorsal midline of the body by membranes (united in H. papillatus, free in H. atrizona). Hoplomyzon is redefined to include the new species. Apure (Cuenca Rio Orinoco) de Venezuela occi- dental. Se distingue de las otras especies del genero (H. atrizona y H. papillatus), porque tiene la sig- uiente combination de caracteres: ( 1 ) El borde an- terior del hocico es ligeramente bilobulado (vs. visiblemente bilobulado en H. papillatus y recto en H. atrizona). (2) No posee barbillas en el rictus como H. atrizona. (3) Posee cuatro papilas en el labio superior, a diferencia de H. papillatus que posee tres (o cinco si incluimos el par rictal). (4) Radios dorsales i5 (vs. i6 en H. atrizona e i3i en H. papillatus). (5) Las barbillas maxilares son lar- gas pero no sobrepasan el punto de nacimiento de la aleta pectoral (18.8% de el largo estandar). (6) Los escudos de la linea lateral describen un zigzag moderado hasta un punto ubicado aproximada- mente en la mitad de la aleta dorsal, pero de ahi en adelante forman una linea recta hasta el pe- dunculo caudal (en H. papillatus se presentan en zigzag a lo largo de toda la linea lateral, y en H. atrizona forman una linea recta sobre toda la linea lateral). (7) El segundo radio de la aleta pelvica es ligeramente mayor que los restantes (forma un fi- lamento en H. papillatus y es corto en H. atrizona). (8) Las aletas dorsal y anal, estan unidas a la linea media del cuerpo mediante unas membranas (es- tan unidas en H. papillatus y no unidas en H. atrizona). Hoplomyzon esta redefinido para incluir la especie nueva. Resumen Una especie nueva de bagre aspredinido de la tribu Hoplomyzontini, Hoplomyzon sexpapilos- toma, especie nueva, fue colectado durante un in- ventario general de los peces de la cuenca del Rio Introduction Since 1978, one of us (D.C.T.) has made col- lections of fishes in the Apure River drainage of western Venezuela as part of a general inventory of the ichthyofauna. While working up the aspre- dinid material, we identified two new records for TAPHORN & MARRERO: HOPLOMYZON SEXPAPILOSTOMA Table 1. Comparison of mensural characters for the type specimens of the three species of Hoplomyzon and ten paratypes of H. sexpapilostoma (as thousandths of SL). H. atrizond* H. papillatus* KM Nil //. papilostoma CAS MCNG Paratypest Character 36495 94908 18669 Min. Max. Mean Standard length, mm 24.0 16.9 22.7 16.3 32.0 22.7 Body depth 142 136 132 96 153 125 Predorsal length 400 408 414 382 434 410 Dorsal fin height 179 147 181 148 245 195 Caudal peduncle length 250 254 303 275 310 296 Caudal peduncle depth 42 47 35 27 40 32 Caudal fin length — 207 189 165 227 196 Pre-anal fin length 529 527 509 495 569 528 Anal fin base length 225 224 145 104 209 157 Anal fin height 200 154 215 226 280 252 Pre-pelvic fin length 300 325 290 287 346 322 Pelvic fin length 221 183 167 153 203 170 Pelvic fin interspace 83 83 68 70 137 86 Pectoral spine length 212 189 156 159 216 187 Anterior branched pectoral ray length 246 195 150 160 184 168 Posterior cleithral process length 125 101 62 31 85 55 Posterior coracoid process length 108 89 99 63 103 81 Dorsomedian head length 263 272 246 231 288 260 Width between pectoral insertions 296 237 227 184 234 208 Head depth at occiput 138 136 107 106 134 119 Snout length 108 107 99 12 30 19 Eye diameter 25 12 18 11 20 14 Interorbital width 75 95 55 65 100 79 Width between anterior nostrils 67 83 46 35 61 52 Mouth width 79 83 73 61 86 74 Barbel lengths Maxillary 195 130 198 152 211 182 Lateral mental 92 71 46 34 69 59 Medial mental 50 41 40 26 52 41 ♦From Stewart (1985). t Based on mcng 5376 (6), mcng 6439 (2), and mcng 18741 (2). the genus Xiliphius, tentatively identified as X. lep- turus and X. melanopterus; three species ofBuno- cephalus, including possibly two new species; Ernstichthys anduzei; and the new species of Hop- lomyzon described herein. Methods Counts, measurements and terminology follow Stewart (1985). As part of a review of the family Aspredinidae in Venezuela, we have prepared cleared, alizarin- stained skeletons of Xiliphius cf. lepturus, Ernst- ichthys anduzei, and Bunocephalus amaurus. These were compared with seven similarly prepared skel- etons of//, sexpapilostoma. Abbreviations for institutions are: Field Mu- seum of Natural History, Chicago, fmnh; Florida Natural History Museum, Gainesville, uf; Museo de Biologia, Universidad Central de Venezuela, mbucv; Museo de Ciencias Naturales de Guanare, mcng; Museu de Zoologia da Universidade de Sao Paulo, Sao Paulo, mzxjsp; Swedish Museum of Natural History, Stockholm, nrm; Zoologisch Museum Amsterdam, zma; California Academy of Sciences, cas. Hoplomyzon Myers, 1942 Hoplomyzon Myers, 1942, pp. 94-95; Hoplomyzon atrizona Myers, 1 942, type species by original des- ignation. Stewart, 1985, p. 5 (redefinition). FIELDIANA: ZOOLOGY Fig. 1. Hoplomyzon sexpapilostoma. A, Most common color pattern (holotype). B, Color pattern of large adults, in this case a male (mcng 18741). C, Caudal fin blotch, lateral view (holotype). D, Ventral view of the anterior part of Hoplomyzon sexpapilostoma (holotype). Scale bars are 2 mm. Diagnosis— (Stewart, 1 985, modified to include new species.) Distinguished from all known as- predinids by having four or five stout, fleshy pa- pillae on upper lip. Differs further from other gen- era of Hoplomyzontini in having 9 or 1 1 pre-anal fin plates, with three or four "paired elements"; the pectoral spine length (excluding flexible tip) less than 25% standard length; and relatively short posterior cleithral and coracoid processes; resem- bles Dupouyichthys, but differs from Ernstichthys in having relatively deeper caudal peduncle, great- er width between anterior nostrils, and wider in- terorbital (table 1). Key to Species of Hoplomyzon Myers la. Dorsal rays i3i; upper lip with three stout, fleshy papillae plus one at each rictus of mouth for a total of five; rictal barbels lacking; os- sified lateral-line tubules arranged in a zigzag pattern from near opercle to base of caudal fin . . . Hoplomyzon papillatus Stewart, 1985 1 b. Dorsal rays i5 or i6; upper lip with four stout, fleshy papillae plus either a slender barbel or a stout fleshy papilla at each rictus for a total of six; ossified lateral-line tubules arranged in a straight line or zigzag to beneath dorsal fin and then continuing posteriorly in a straight line 2 2a. Each rictus with a slender barbel; dorsal rays i6; ossified lateral line tubules arranged in straight line Hoplomyzon atrizona Schultz, 1 944 2b. Each rictus with a stout fleshy papilla; dorsal rays i5; ossified lateral-line tubules arranged in a zigzag to beneath dorsal fin . . Hoplomyzon sexpapilostoma, new species TAPHORN & MARRERO: HOPLOMYZON SEXPAPILOSTOMA Fig. 2. A, B, Hoplomyzon sexpapilostoma (mcng 5376). C, D, Ernstichthys anduzei (mcng 1 3845). E, F, Bunoceph- alus amaurus (mcng 6038). G, H, Xiliphius cf. lepturus (mcng 5547). A, C, E, and G show ventral views of the pectoral and pelvic girdles (with elements of right pectoral fin omitted). B, D, F, and H show dorsal views of pectoral girdle and left cleithral process. Scale bars are 2 mm. abf = abductor fossa; bpt = basipterygium; cl = cleithrum; co = coracoid; pc = posterior cleithral process; pfr = pectoral fin radials (after Schaefer, 1987). Hoplomyzon sexpapilostoma, new species, Figures 1-4. Holotype— mcng 18669, 22.70 mm standard length, Venezuela, Barinas State, Apure River Drainage, Rio Masparro at site of Masparro Dam, 70°06'00"W, 8°50'40"N, bottom rock rubble, gravel and sand with large exposed boulders. While we were fishing, the river was diverted through tun- nels to expose the dam site and the reach was rapidly drying up. Specimens were collected with hand nets from the remaining puddles between 1430 and 1645 by D. Taphorn and C. Lilyestrom, 13 November 1983. Paratypes— mcng 5376 (70 specimens); mzusp 38894 (5); fmnh 97762 (5); mbucv 17791 (7); and nrm A88/ 1983457.4231 (5); all taken with holotype. Unless in- dicated otherwise, following lots are all from Venezuela, Portuguesa state (field numbers follow dates): mcng 38 1 (6), Guanare River in La Raya, about 28 km N of Gua- nare, 6 June 1979, DCT79-70, D. Taphorn, C. Lilyes- trom. mcng 382(12), Tucupido River about 2 km south of Highway 5 bridge, 27 Feb. 1979, DCT79-30, D. Ta- phorn, C. Lilyestrom, E. Salas, R. Feo, G. Feo. mcng 5480 (4), border of Barinas and Portuguesa states, Bo- cono River about 1 km below dam site, 5 Nov. 1982, DCT82-72, D. Taphorn, C. Lilyestrom, C. Olds, S. Reid, J. Reid, M., L. and W. Lilyestrom. mcng 6439 (2), state of Tachira, Frio or Torbes River, about 35 km southeast of San Cristobal, 27 May 1982, DCT82-46, D. Taphorn, C. Lilyestrom, C. Olds, mcng 8530 (4), Tucupido River at dam site, 15 Jan. 1981, DCT81-1, D. Taphorn, C. Lilyestrom, A. Fernandez, mcng 8968 (1), Tucupido River near town of Tucupido, 16 Jul. 1980, DCT80-73, D. Taphorn, C. Lilyestrom, L. Nico. mcng 9805 (5), creek at bridge 30 km north of Guanare on road to FIELDIANA: ZOOLOGY Fig. 2. Continued. Biscucuy, 3 1 May 1980, DCT80-66, D. Taphom, S. Reid, C. Staver, J. Karr. mcng 11825 (1), Moroturo River about 1 5 km north of Aparicion, 1 2 Aug. 1 983, DCT83- 28, D. Taphorn, C. Lilyestrom, E. Sutton, J. Sanchez. mcng 15507 (2), Guanare River at Guanare just below dam for irrigation system, 1 7 Jan. 1 984, KW84-2, K. Winemiller. mcng 18741 (2), Saguas River, near bridge, in park on road to Chabasquen, 1 May 1988, ASF88-2, A. Flecker, mcng 18905 (2), Guache River, 2 May 1988, ASF88-3, A. Flecker, mcng 18906 (7), Barinas, Yuca River, 3 May 1988, ASF88-4, A. Flecker, mcng 19279 (1), Bocono River below dam, 1 1 Jul. 1988, MC88-1, A. Barbarino. mcng 19780 (4) Rio Las Marias about 5 km NW of El Potrero, 1 8 Dec. 1 988, ASF88-9, A. Beck- er, B. Feifarek, C. Marrero, N. Camargo, M. Jimenez. Diagnosis— Hop lomyzon sexpapilostoma is distinguished from all known aspredinids by the following combination of characters: (1) Anterior border of snout but slightly emarginate (figs. 1 a, b, d) vs. deeply emarginate in H. papillatus or nearly straight in H. atrizona. (2) No barbels at rictus of mouth as in H. atrizona (fig. Id). (3) Four papillae on upper lip (fig. Id) instead of three as in H. papillatus. (4) Dorsal rays i5 vs. i6 in H. atrizona and i3i in H. papillatus. (5) Maxillary barbels long but not surpassing pectoral origins (18.8% SL). (6) Ossified lateral-line tubules ar- ranged in zigzag pattern to point beneath the center of dorsal fin base, but straight from there back to caudal peduncle (in H. papillatus the zigzag pattern continues to caudal peduncle, in H. atrizona the line is completely straight). (7) Second pelvic ray slightly longer than other pelvic rays (it forms a filament in H. papillatus and is short in H. atri- TAPHORN & MARRERO: HOPLOMYZON SEXPAPILOSTOMA Fig. 3. Ventral elements of cleared and stained specimens. A, A 17.9 mm SL of Hoplomyzon sexpapilostoma (mcng 5376). B, A 26.2 mm SL of Hoplomyzon sexpapilostoma (mcng 5376). C, Ernstichthys anduzei (mcng 1 3845). The black dots represent the anus. Scale bars are 2 mm. zona). (8) Dorsal and anal fins united to dorsal midline of body by membranes (united in H. pa- pillatus, free in H. atrizona). Description— Mensural characters are present- ed in Table 1 for comparison with other species of Hoplomyzon. Anterior nostril on short tube, situated just behind anterior margin of snout and directed anteriorly (figs, la, b). Posterior nostril not very close to eye, about equidistant from an- terior nostril and the eye, with lunate opening much smaller than eye diameter. Maxillary barbel sup- ported by a bony element that extends for about one fourth of its length. Posterior coracoid pro- cesses extend far back and form lyre within which anterolateral processes of pelvic bone are included (fig. 2a). Lower caudal fin lobe longer than upper (fig. lc). Meristic Data— Dorsal fin i5; pectoral I5i; pec- toral spine with 4—5 teeth on posterior margin, anterior margin smooth (fig. 2a); flexible part of pectoral spine 3 1 .7% of its total length; pel vies i4i, none of rays filamentous; anal fin ii5 or iii5; caudal i7i, with five rays attached to upper hypural and four to lower (this characteristic apparently unique to the Hoplomyzontini among all known catfish- es); branch iostegal rays four; dorsal plates 2 1 ; pre- anal plates nine (figs. 3a, b); ventral plates 14; ossified lateral-line tubules 4 1 . Pigmentation— Three dark conspicuous cross- bands on dorsum— first begins at point near dorsal origin and other two cross body between the dorsal fin and tail (fig. la); caudal fin with dark blotch at base that covers bases of upper eight rays but does not extend onto bottom ray (fig. lc). Females (and probably immatures of both sexes) with thin, black, masklike band that passes vertically through eyes (fig. la). Band is wider in some adults and whole anterior portion of head dark (fig. lb). Pectoral spine with small black central blotch, extending onto membrane that unites spine with first branched ray (fig. la); spot larger and darker in males (fig. 1 b). Areas between dark bands on body, anterior band through eyes, and maxillary barbels light tan. Area posterior to mask, and dorsum to just anterior to first dark band across body brown. Venter beige except where dark lateral bands con- tinue ventrally. Distribution— So far found only in the Apure River drainage in Andean rivers and streams at altitudes from about 90 to 600 m. They have been found living sympatrically with Ernstichthys an- duzei at the localities given by Stewart (1985). Comments— Hoplomyzon sexpapilostoma is in- termediate between the two described species for some characters; however, its several unique char- acters, and the morphometric and meristic difler- FIELDIANA: ZOOLOGY A B Fig. 4. Caudal vertebra in lateral (a) and frontal (b) views, and caudal skeletons. A, D, Hoplomyzon sexpapilostoma (mcng 5376). B, E, Bunocephalus amaurus (mcng 6038). C, F, Xiliphius cf. lepturus (mcng 5547). Ct = centrum, He = hemal canals, HY = hypurals, Nc = neural canals, PH = posterohyal. Scale bars are 2 mm. ences, justify species status. We believe that the character given as typical for the genus Hoplomy- zon by Stewart (1985), 1 1 preanal plates with only four paired elements, should be modified to 9 or 1 1 preanal plates to include Hoplomyzon sexpa- pilostoma. Comparison of the osteology of Hoplomyzon sexpapilostoma with that of other aspredinids has revealed several important features. The so-called dermal plates along the dorsum and venter, and the "paired elements" of the belly (figs. 3a, b), are actually the expanded, flattened tips of bony struts (probably modified neural and hemal spines) that extend from the highly compressed vertebrae to the skin. They extend both dorsally and ventrally to join the vertebrae to the external plates and form a sort of X-shaped girder (fig. 4a) with two centers (the neural and hemal canals). We have found these girders in Hoplomyzon sexpapilosto- ma and Ernstichthys anduzei but they are absent in Bunocephalus amaurus (fig. 4b) and Xiliphius cf. lepturus (fig. 4c). Thus the vertebrae and struts form a solid bony connection from the top to bottom of the fish. Opposing plates are separate from each other in front of and next to the dorsal and anal fin bases, but fuse on the dorsal and ventral midlines behind the dorsal and anal fin bases, respectively. The pairs are larger and closer to each other behind the dorsal and anal fin bases. The attachment of bifid neural spines to dermal plates in the loricariid Hypostomus plecostomus described by Schaefer ( 1 987) is similar to the condition observed in Hop- lomyzon sexpapilostoma. However, H. plecosto- mus lacks bifid hemal spines, and the single hemal spines are expanded on the posterior vertebrae, not unlike the condition observed in Bunocephalus and Xiliphius. In Hoplomyzon sexpapilostoma (figs. 2a, b) and Ernstichthys anduzei (figs. 2c, d) the pelvic girdle and fins are situated between the elongated pos- teriorly projecting processes of the pectoral girdle (inside the "lyre"). This contrasts greatly with the condition observed in Bunocephalus amaurus (figs. 2e, f) and Xiliphius cf. lepturus (figs. 2g, h), in which the pelvic girdle is situated much farther posteri- orly. The greatly reduced number of caudal rays i7i, TAPHORN & MARRERO: HOPLOMYZON SEXPAPILOSTOMA with five attached to the dorsal hypural plate (fig. 4d), is unique among known catfishes (Lundberg & Baskin, 1969). Bunocephalus and Xiliphius have i8i with five on each hypural (figs. 4e, f). Ecology— Hoplomyzon sexpapilostoma typi- cally inhabit small Andean rivers or creeks with a gravel to boulder substrate and moderate to high current. Water temperatures are usually between 24 and 28° C. Water is typically clear and flow is greatly reduced during the dry season (November- May), but flow is violent and turbidity high during the rainy season. We speculate that their peculiar skeletal struc- tures are an adaptation to living in the interstices of a constantly shifting substrate of gravel. These fish may have evolved structural struts that serve to protect them from being crushed when trapped inside an "avalanche" of small stones. Among the aspredinids we have examined, we have found this condition only in the Hoplomyzontini, all of which live in similar habitats. In contrast, Xiliphius live buried in the bottoms of larger rivers in sand or mud substrates. Bunocephalus are usually taken from among leaf litter in small forest streams. This new species and all other members of the Hoplomyzontini are cryptically colored, with al- ternating light and dark disruptive bands. This distinct, alternating pattern is not known among other aspredinids, though all are cryptically col- ored to some degree. Nothing is known about the reproduction of this species, although the females of the type series were ripe with relatively large, yellowish eggs in November (beginning of the dry season). The ob- served sexual dimorphism (mature males were consistently larger and had a different color pat- tern) suggests that some sort of courtship might be expected. Although H. sexpapilostoma is small in size, and a seemingly insignificant species, it may play an important role in the trophic continuum of trop- ical Andean rivers. The collection of some 70 spec- imens when a section of the Masparro River was dried indicates that they are present in fairly high density, and that their rarity in collections is due to the usually inaccessible habitat that they occupy (we were able to collect hundreds of Xiliphius cf. lepturus under similar circumstances when a dam was closed on the neighboring Bocono River). Stomach content analyses revealed a diet of ben- thic macroin vertebrates, mainly aquatic insect lar- vae (Ephemeroptera). These insects probably shred leaves (Vannote et al., 1 980) as a food source. Thus this catfish is a predator on the organisms that capture and introduce fine particulate organic mat- ter into the riverine foodweb. Etymology— From the Latin sex = six and pa- pilo = papilla (tubercle), the Greek stoma = mouth. The name refers to the presence of six buccal pa- pillae (four on upper lip, one at each corner of mouth) that distinguish the species from its con- geners. Status of the Hoplomyzontini In the description of Ernstichthys anduzei, Fer- nandez Y. (1953) recognized two families in the order Asprediformes: the Aspredidae (to include Aspredo and other long anal fin-based aspredin- ids), and the Bunocephalidae (for most other gen- era) and proposed the division of the Bunoce- phalidae into two subfamilies: Bunocephalinae for Bunocephalus, Xiliphius, Agmus, etc. and Hop- lomizontinae for Hoplomyzon, Dupouyichthys, and Ernstichthys. As presently defined, the clas- sification of these fishes is essentially the same, but Asprediformes is not used, and each subordinate level has been "demoted" one notch so that the family Aspredinidae comprises the subfamilies Aspredininae (e.g., Aspredo) and Bunocephalinae, with the latter subdivided into the tribes Buno- cephalini (Bunocephalus, Xiliphius, etc.) and Hop- lomyzontini (Hoplomyzon, Ernstichthys, and Du- pouyichthys) as defined by Myers (1942) and Stewart (1985). Both Fernandez Y. (1953) and Stewart (1985) considered the "superficial" bony plates as unique derived features that provide ev- idence for the monophyletic status of the Hoplo- myzontini. Our observations on structure of the vertebrae, position of the pelvic girdle, the unique reduction of caudal elements, and banded pig- mentation (table 2) are further evidence for mono- phyly of the Hoplomyzontini and widen the mor- phological gap that separates these tiny catfishes from other aspredinids. Further osteological anal- yses will probably reveal that the currently rec- ognized genera should be regrouped into subfam- ilies distinct from those currently recognized. Because we lack comparative material on Aspre- dininae at this time, we cannot resolve phyloge- netic relationships. However, based on our find- ings noted above, and the overall morphological similarity apparent in the few illustrations of As- predininae available, we suggest as a working hy- pothesis of relationship that the Aspredininae will prove to be more closely related to the Buno- FIELDIANA: ZOOLOGY Table 2. Character comparison of the tribes Hoplo- myzontini and Bunocephalini. 1 1 o p In m y/o n t i n i — Hoplo- myzon, Ernstichthys, and Dupouyichthys (not yet seen) Bll 11 hi epha I i ii i Huno- cephalus and Xiliphius 1) Caudal vertebrae in form of an "X." 2) Pelvic girdle anterior; anterior extensions of the pelvic bone includ- ed inside arch formed by posterior coracoid processes. 3) Preanal plates present. 4) Principal caudal rays 5+4. 5) Pigmentation pattern of alternating light and dark bands. 6) Dorsum and venter with series of paired dermal plates. Vertebrae in form of a cross. Pelvic girdle posterior; anterior extensions of the pelvic not included in arch formed by pos- terior coracoid process- es. No preanal plates. Principal caudal rays 5 + 5. Pigmentation uniform or mottled, not banded. No dermal plates. cephalini, sharing the characters of a posterior pelvic girdle placement and a nonbanded color pattern (although these characters may prove to be plesiomorphous once the character states have been polarized with outgroup comparisons), as well as the relatively simple cross-shaped vertebrae that lack the dorsal and ventral extensions. Acknowledgments We thank the many collectors listed above who helped collect the types. Drs. John Lundberg and Donald Stewart, Mr. Leo Nico, and one anony- mous reviewer reviewed the manuscript and pro- vided many useful suggestions. The Research Of- fice of unellez and FUNDACiTE provided funds for the Apure River Ichthyological Inventory. Cris- pulo Marrero drew the illustrations. Literature Cited Fernandez Yepez, A. 1953. Algunas notas sobre los peces Asprediformes con description de Ernstichthys anduzei, nuevo e interesante Bunocephalido. Nove- dades Cientificas, Ser. Zool., Museo de Historia Nat- ural La Salle, 11: 1-7. Lundberg, J., and J. Baskin. 1969. The caudal skel- eton of the catfishes, order Siluriformes. American Museum Novitates, 2398: 3-49. Myers, G. 1942. Studies on South American fresh- water fishes. I. Stanford Ichthyological Bulletin, 2(4): 89-1 14. Schaefer, S. 1987. Osteology of Hypostomus plecos- tomus (Linnaeus), with a phylogenetic analysis of the loricariid subfamilies (Pisces: Siluroidei). Contribu- tions in Science, Natural History Museum of Los An- geles County, 394: 1-31. Stewart, D. 1985. A review of the South American catfish tribe Hoplomyzontini (Pisces, Aspredinidae), with descriptions of new species from Ecuador. Fieldi- ana: Zoology (New Series), 25: 1-19. Vannote, R., G. Minshall, K. Cummins, J. Sedell, and C. CusHrNG. 1 980. The river continuum con- cept. Canadian Journal of Fisheries and Aquatic Sci- ences, 37: 130-137. TAPHORN & MARRERO: HOPLOMYZON SEXPAPILOSTOMA Field Museum of Natural History Roosevelt Road at Lake Shore Drive Chicago, Illinois 60605-2496 Telephone: (312)922-9410