South American freshwater needlefishes (Belonidae) of the genus Pseudotylosurus

Pseudotylosurus Fernández Yépez is considered a valid genus of Belonidae based on the following combination of characters: depressed caudal peduncle; long narrow side branches to lateral line; pleural ribs attached to fourth vertebra; nasal papilla spatulate; lower pharyngeal plate and upper pharyngeal bones two and three elongate. Two species are recognized: Ps. microps (Günther) and Ps. angusticeps (Günther). Belone amazonica Steindachner and Deltatylosurus guayoensis Martin are synonyms of Ps. microps; Ps. brasiliensis Fernández Yépez is a synonym of Ps. angusticeps. Ps. microps reaches a larger size than Ps. angusticeps and occurs primarily in the Orinoco, the Guianas, and the lower Amazon. Ps. angusticeps is primarily a species of the upper Amazon in Peru and Ecuador, Parana and the Paraguay. Ps. angusticeps differs from the more generalized Ps. microps in having ctenoid scales; more anal fin rays (usually 17-19 compared to usually 14-16); a much narrower interorbital region that lacks scales; fewer branchiostegal rays (usually 9 compared to usually 10 or 11); shorter postorbital distance (13.3-15.0 vs. 15.3-18.3% BL); and a shorter preopercle length (9.3-10.7 vs. 10.5-12.7% BL).