A new species of freshwater ariid catfish has been described from the Usumacincta River draiange in Guatemala and Mexico.
Naming the new catfish Potamarius usumacinctae after the river drainage in which the fish is found in the latest issue of Copeia, Ricardo Betancur-R and Philip Willink distinguish it from other Central American freshwater ariids by a combination of the following features: 17"20 lateral gill rakers on the first gill arch, well developed mesial gill rakers on the first two gill arches, presence of accessory tooth patches on palate, premaxillary tooth band length 2.4"2.9 in its width, snout length 1.4"1.8 in postorbital length, maxillary barbel not extending behind the gill membrane, and the absence of a dorsomedian fleshy groove on head.
There are two other species of Potamarius from Central America: P. izabalensis (from the Izabal Lake drainage) and P. nelsoni (from the Usumacincta River drainage), both of which differ from P. usumacinctae in lacking palatal teeth and having a narrower premaxillary tooth band and longer snout.
For more information, see the paper: Betancur-R, R and PW Willink (2007) A new freshwater ariid (Otophysi: Siluriformes) from the Ro Usumacinta basin. Copeia 2007, pp. 818"828.