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A new species of the rare genus Trichogenes is reported on the basis of specimens without locality and other associated data. The obvious distinctiveness, taxonomic relevance, and phylogenetic importance of the new taxon justify its description with material at hand. Trichogenes beagle, new species, differs from all congeners by the presence of tricuspidate teeth on its jaws; by the distribution of opercular odontodes along a wide area of the margin of the opercle; by the pale integumentary pigmentation, composed of few scattered small spots on dorsum and flanks, but lacking large spots near the base of the anal fin; and by the absence of differential concentration of dark chromatophores along the base of the dorsal fin. The new species differs further from each of its two congeners, T. longipinnis and T. claviger, by various additional traits of internal and external morphology and pigmentation. Trichogenes beagle seems to be the closest relative of T. claviger, the two species sharing a number of putatively derived traits not present in T. longipinnis, such as the presence of a large anterodorsal clawlike process on the neural arches of the anterior four free vertebrae. The three species now included in Trichogenes share all synapomorphies previously proposed for the genus, thus strongly supporting generic monophyly. The enigmatic disc-shaped orbital bone in T. beagle and congeners is homologous to a topologically equivalent rodlike structure in other trichomycterids. New comparative information corroborates the hypothesis that the bone is a neomorphic structure, here called the barbular bone. Previous proposals of its homology with the antorbital or supraorbital are refuted. Ontogenetic data demonstrate that the anterior element of the infraorbital series in trichomycterids is a fusion between the lacrimal and antorbital, as postulated—but previously poorly demonstrated—for other catfishes. The structure of the opercle in the new species is intermediate between the highly derived morphology in most trichomycterids and the plesiomorphic condition in other loricarioids, helping to understand the evolution of the opercle of trichomycterids. New information on T. claviger is reported on the basis of additional material.

Four new species of the trichomycterid subfamily Glanapteryginae are described from the Rio Orinoco basin of Venezuela. Two new species each in Pygidianops Myers 1944 and Typhlobelus Myers 1944 represent the first documented occurrence of these genera in Venezuela, and for Pygidianops the first occurrence outside the Rio Negro basin. The new species were captured from sand-bottom habitats in two disparate locations in the Orinoco River basin and display a remarkable suite of reductive features, such as loss of eyes, fins, and pigment, and reductions or absence of laterosensory canals and odontodes. Pygidianops cuao, n.sp. from the Rio Cuao, a clear-water tributary of the upper Orinoco River, is diagnosed from its congeners by the presence of diminutive eyes and a triangular skin flap at the corner of the mouth. Pygidianops magoi, n.sp., known from near the delta of the Orinoco River, is diagnosed from its congeners by the absence of pectoral and anal fins, presence of four laterosensory pores, an...

A well-developed second ural half-centrum is a peculiar characteristic of the caudal skeleton of certain siluriforms, not seen in other Recent ostariophysans. Although the character has been previously recorded in the literature, its exact taxonomic distribution, structure, ontogeny, and phylogenetic meaning within siluriforms are not yet determined. In this paper, the degree of development of the second ural half-centrum is surveyed across the order. The ontogeny of the relevant axial structures in the posterior region of the vertebral column is reported in representative siluriform taxa. The condition where the second ural centrum is well formed and forms a complete intervertebral joint anteriorly with the compound caudal centrum is considered derived within siluriforms, a character state homoplastic with the primitive state in more distant teleostean outgroups. Various catfishes display that derived condition, which is informative about relationships at different levels within the group. The most inclusive of those clades is the superfamily Sisoroidea, including the families Amblycipitidae, Akysidae, Sisoridae, Erethistidae, and Aspredinidae. The placement of the neotropical Aspredinidae into an otherwise exclusively Asian clade has important biogeographical implications and the structure of the second ural centrum provides additional support to that hypothesis. Based on the currently available knowledge on the relationships among catfishes, a well-developed second ural centrum is hypothesized to be a result of six different events in siluriforms.