Tetragonopterus Cuvier, 1816

Tetragonopterus Cuvier, 1816: 166 . Type species: Tetragonopterus argenteus Cuvier, 1816 . Type by monotypy. Gender: masculine.

Diagnosis. Tetragonopterus is diagnosed within the Characidae [except the Stethaprioninae and Stichonodon insignis (Steindachner, 1876)] by the presence of only three supraneurals (vs. more than three supraneurals) and a branched laterosensory canal in the sixth infraorbital (vs. unbranched laterosensory canal). In addition, Tetragonopterus can be diagnosed from other characids, including Stethaprioninae and S. insignis, by the presence of a lateral line strongly bent downward anteriorly (vs. lateral line straight or only slightly curved), its relative deep body, absence of a predorsal spine, a complete lateral line, and the presence of five multicuspidate teeth in the inner row of the premaxilla.

Distribution. Tetragonopterus is widely distributed across the cis-Andean South American freshwaters, including the Amazon, Orinoco, Guianas, Parnaíba, Jaguaribe, Itapicuru, Paraguaçu, São Francisco, Paraguay, and lower Paraná river basins (Fig. 2).

Etymology. Tetra from Greek, meaning four; gonia from Greek, meaning angle; pteron from Greek, meaning fin, in a clear allusion to the evident tetragonal shape of the body.