STERNOPYGUS XINGU, A NEW SPECIES OF ELECTRIC FISH FROM BRAZIL (TELEOSTEI, GYMNOTOIDEI), WITH COMMENTS ON THE PHYLOGENETIC POSITION OF STERNOPYGUS

A new species of gymnotoid knifefish in the genus Sternopygus is descr ibed from the Rio Xingu of Brazil. A data matrix of 52 characters for the four recognized species of Sternopygus and representative outgroup taxa is presented. The data include 12 characters diagnostic of the S ternopygidae, 11 characters supporting the monophyly of Sternopygus, a nd 15 characters structuring a hypothesis of relationships among the f our species of Sternopygus. Variation among and between populations of Sternopygus from many localities in South America remains to be analy zed for a robust hypothesis about numbers of species and their interre lationships. Characters of the genus thought to be plesiomorphic withi n the Gymnotoidei are discussed in relation to the proposed phylogeny. Implications of this phylogeny on the biogeographic history of Sterno pygus are noted. A key to the recognized species of Sternopygus is pro vided.