Sternopygus castroi, a new species of Neotropical freshwaterelectric fish, with new synapomorphies to the genus (Sternopygidae: Gymnotiformes:Teleostei).

Sternopygus castroi n. sp. is described as a new species of sternopygid Neotropical freshwater fish from the Rio Cuieiras, tributary of Rio Negro, Amazonas State, Brazil. It differs from the other species of the genus by a combination of characters. Three new synapomorphies for Sternopygus are reported. Only Sternopygus species present a membranous integumental subopercular fold originating postero-ventrally in the opercular region, running anteriorly to the isthmus region. In Sternopygus, the membranous opercular opening is wide and S-shaped (wide but fleshy in Gymnotus). In Sternopygus there is also a medial cephalic fleshy fold at the ventral margin of the opercular membrane, directed forward and ventrally to the isthmus, surrounding the anal pore anteriorly, just behind the subopercular flap. [ABSTRACT FROM AUTHOR]