New Rhynchodoras

[Silurus]

Birindelli, JLO, MH Sabaj & DC Taphorn, 2007. New species of Rhynchodoras from the Río Orinoco, Venezuela, with comments on the genus (Siluriformes: Doradidae). Copeia 2007: 672–684.

Abstract

A new species of proboscoid thornycat, Rhynchodoras castilloi, is described from the Río Apure, Orinoco basin, Venezuela. The new species is distinguished from R. woodsi (Essequibo and Amazon basins minus Xingu and Tocantins basins) by having a simple gas bladder (vs. each posterior chamber of gas bladder expanded into elongate horn-like diverticulum) and tubercles punctate and abundant (vs. tubercles elongate, dash-like, and sparse). The new species is distinguished from R. xingui (Xingu and Tocantins basins) by having all three tympanal scutes weakly developed (vs. second and particularly third well developed, latter with medial carina), midlateral scutes modally 35 per side, range 34–36 (vs. 34, range 33–34), and anterior midlateral scutes relatively shallow, depth about one-fifth (vs. about one-third to one-quarter) of corresponding body depth, with weakly developed dorsal and ventral laminae lacking distinct serrations along posterior margins (vs. dorsal and ventral laminae of midlateral scutes well developed with conspicuously serrated posterior margins). The type species, R. xingui, is distinguished from R. woodsi by having a simple gas bladder (vs. with two posterior horn-like diverticula), midlateral scutes modally 34 per side, range 33–34 (vs. 35, range 34–37), and anterior midlateral scutes with conspicuous medial thorns (vs. thorns absent or weak, procumbent). Notable features of the genus are discussed, including jaw and gas bladder morphology, development of anterior nuchal plate, presence of multiple pores in skin beneath postcleithral process, and tubercle morphology and distribution. Shared derived characters suggest a sister-group relationship between Rhynchodoras and Rhinodoras plus Orinocodoras.