SYSTEMATICS OF THE GENUS HYPOPTOPOMA GU¨ NTHER, 1868 (SILURIFORMES, LORICARIIDAE) ADRIANA E. AQUINO Division of Vertebrate Zoology American Museum of Natural History ([email protected]) SCOTT A. SCHAEFER Division of Vertebrate Zoology American Museum of Natural History ([email protected]) BULLETIN OF THE AMERICAN MUSEUM OF NATURAL HISTORY Number 336, 110 pp., 45 figures, 18 tables Issued June 3, 2010 Copyright E American Museum of Natural History 2010 ISSN 0003-0090 CONTENTS Abstract.......................................................... 3 Introduction . ...................................................... 3 Methods.......................................................... 4 Meristics . ...................................................... 4 Fin-rays....................................................... 4 Teeth......................................................... 5 Plates . ...................................................... 5 Morphometrics.................................................... 5 Anatomy........................................................ 5 PhylogeneticAnalysis............................................... 6 ScopeandOrganization............................................. 6 Abbreviations..................................................... 7 Systematics........................................................ 7 Hypoptopoma Gu¨nther,1868a......................................... 7 GeneralMorphology............................................... 14 Neurocranium.................................................. 16 Infraorbital series and laterosensory canals ............................. 17 Suspensorium and mandibular arch................................... 17 Opercularseries................................................. 17 Weberian apparatus and axial skeleton ................................ 18 Median fins ................................................... 20 Paired fins .................................................... 21 Key to the species of Hypoptopoma .................................... 22 Hypoptopoma baileyi, new species. ................................... 23 Hypoptopoma guianense Boeseman, 1974................................. 28 Hypoptopoma psilogaster Fowler, 1915 .................................. 32 Hypoptopoma thoracatum Gu¨nther, 1868a ................................ 38 Hypoptopoma brevirostratum,newspecies................................ 43 Hypoptopoma muzuspi, new species. ................................... 48 Hypoptopoma spectabile (Eigenmann,1914)............................... 52 Hypoptopoma sternoptychum (Schaefer, 1996) ............................. 55 Hypoptopoma bianale, new species . ................................... 59 Hypoptopoma inexspectatum (Holmberg,1893)............................ 60 Hypoptopoma elongatum,newspecies................................... 67 Hypoptopoma incognitum, new species................................... 72 Hypoptopoma steindachneri Boulenger, 1895 .............................. 77 Hypoptopoma gulare Cope, 1878 . ................................... 85 Hypoptopoma machadoi, new species. ................................... 91 Phylogenetic Analysis ................................................ 94 Character Descriptions and Coding . ................................... 94 Topology and Character Support . ................................... 99 Biogeographical Implications ........................................ 101 References....................................................... 104 Appendix........................................................ 109 ABSTRACT The systematics of Hypoptopoma Gu¨nther (1868a) is revised based on comprehensive evaluation of specimen collections and a phylogenetic analysis of the species. The genus Hypoptopoma comprises a distinctive assemblage of loricariid catfishes distributed in the lowland drainages of tropical, subtropical, and temperate latitudes of South America to the east of the Andes. Hypoptopoma is uniquely diagnosed among genera of the Loricariidae on the basis of the presence of a laterally expanded nuchal plate. Members of the genus can be further distinguished from all other loricariids, except the hypoptopomatin genus Oxyropsis, by the depressed head with eyes placed ventrolateral and visible from below. Hypoptopoma is further distinguished from all other Hypoptopomatini, including Oxyropsis, by the caudal peduncle posterior to the base of the anal fin ovoid in cross section and deeper in the dorsoventral axis. All species of Hypoptopoma, except H. spectabile, can be further distinguished among loricariids by the presence in adult stages of a column of variably enlarged and flattened odontodes positioned along the posterior margin of the trunk plates. Individuals of several Hypoptopoma species attain the largest body size for the subfamily Hypoptopomatinae, with standard length reaching 105 mm. Species of Hypoptopoma typically occur in streams of slow to moderate current and muddy to sandy bottom with marginal emergent vegetation. Based on verified specimen records, the species is distributed in the Rı´o Amazonas basin, including the Ucayali, Madeira, and Tapajos rivers, as well as in the rivers east to the Ilha Marajo drainage (Para, Brazil), in the Tocantins and smaller coastal river drainages in northeastern Brazil (Mearim), the upper Rı´o Orinoco basin, the Essequibo and Nickerie river basins of the Guiana Shield, and in the rı´os Paraguay and lower Parana´. There are no records of Hypoptopoma in the Rı´o Uruguay, the Atlantic coastal drainages of Uruguay and Brazil south of Rio Mearim (Marana˜o), the upper Parana´, and Rio Sa˜o Francisco systems. Fifteen species are recognized in Hypoptopoma, seven of which are newly described herein. Phylogenetic analysis of Hypoptopoma species, based on analysis of 26 characters drawn from aspects of external morphology and internal osteology, recovered a well-supported but incompletely resolved nested set of clade relationships that suggests a widespread ancestral distribution for the group in central Amazonia, plus at least four instances of divergence of a species having a peripheral distribution from an Amazonian sister group. Relationships at the basal node were unresolved. There was insufficient evidence to resolve the relationships among H. baileyi, n. sp., of the Madeira river basin, an unresolved clade comprised of H. guianense Boesemann, 1974, of the Essequibo and Nickerie basins in Guyana and Surinam; H. psilogaster Fowler, 1915, of the upper Amazon basin in Brazil and Peru; and H. thoracatum Gu¨nther, 1868a, of the upper and middle Amazon basin; and a well-supported clade that includes all other Hypoptopoma species. The latter clade was supported by four synapomorphies and includes H. brevirostratum, n. sp., of the upper Amazon basin in Brazil and Peru, H. muzuspi, n. sp., of the Tocantins basin, and a more restricted clade supported by six character-state changes comprising the remainder of the subfamily. Two species, H. spectabile (Eigenmann, 1914) of the upland Amazon and upper Orinoco river basins of Venezuela, Colombia, Ecuador, and Peru and H. sternoptychum (Schaefer, 1996a) of the lowland reaches of the Amazon river, formerly placed in the genus Nannoptopoma Schaefer, 1996, represent a clade most closely related to a nested subset of Hypoptopoma species. These former Nannoptopoma species are reassigned to Hypoptopoma, thus rendering the former generic name a subjective junior synonym of Hypoptopoma. Hypoptopoma bianale, n. sp., of the upper Amazon River basin in Brazil and Peru represents the sister group to a largely unresolved clade comprised of H. inexspectatum (Holmberg, 1893a) of the Paraguay-Parana´ basin, H. steindachneri Boulenger, 1895, of the upper Amazon basin in Brazil and Peru, H. gulare Cope, 1878, of the upper Amazon basin, H. machadoi, n. sp., of the Orinoco basin, and a clade comprised of H. elongatum, n. sp., of the lower Tapajos and lower Trombetas rivers plus H. incognitum, n. sp., of the middle Amazon basin, Tocantins, and Mearim rivers. A key to the species of Hypoptopoma is provided. INTRODUCTION of tropical South America to the east of the Andes. Among the 716 recognized species of Species of the genus Hypoptopoma com- armored catfishes (Ferraris, 2007), represen- pose a distinctive group of loricariid catfishes tatives of Hypoptopoma are easily recognized distributed throughout the lowland drainages by their seemingly incongruous combination 4 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 336 of a robust trunk, greatly depressed head and al., 2008), but members of the group have not pointed snout, yielding a spatulate form to been the subject of investigation at the species the anterior third of the body. A further level. Moreover, very few of the more consequence of the extreme depresssion of speciose genera of the Loricariidae have been the head and snout in these species is the the subject of taxonomic revisionary studies ventrolateral displacement of the eyes, which involving comprehensive examination of ma- typically occupy a more dorsal position on terial, and even fewer involve taxa with the head in other loricariid catfishes, the species having a geographic distribution on ventrolateral position of the opercle, and a continentwide or international scale (e.g., ventral position of the canal-bearing plate. Parotocinclus—Garavello, 1977; Pterygo- Gu¨nther (1868a, b) erroneously interpreted plichthys—Weber, 1992; Panaque dentex these two latter as a two-bone gill cover, clade—Schaefer and Stewart,