Redescription of Microsternarchus bilineatus (Fernández-Yépez, 1968) (Gymnotiformes: Hypopomidae, Microsternarchini), with the designation of a neotype

ABSTRACT. Microsternarchus bilineatus Fernández-Yépez, 1968 is a small, inconspicuous electric fish distributed in the Orinoco, Amazon and Tocantins basins. Its holotype and paratypes from Río San José, a tributary of Río Guariquito, Orinoco basin, Venezuela, are apparently lost. We examined 14 specimens collected in Río San Bartolo, also a tributary of Río Guariquito, 110 km by river from Río San José. Because of its proximity to the type locality and apparent conformity to the original description, we used these newly collected specimens to redescribe M. bilineatus using external morphology, morphometrics, meristics, and osteology including high-resolution X-ray computed tomography. In order to address geographic variation we compared Río San Bartolo specimens with others of, or close to, M. bilineatus from Casiquiare river and from two streams in Roraima state, Brazil. In our analysis specimens from distant localities differ in the interobital distance and mouth size, number of anal-fin rays and skeletal features in the dentary and cranial fontanelles. Detailed revision of the genus will require a stable description of type species. Therefore, we designate INHS 111262 as neotype for M. bilineatus.