The phylogenetic relationships of the poorly known nominal heptapterid genera Nemuroglanis, Imparales, and Medemichthys, and the validity of their species, are examined on the basis of type- and recently discovered material. These genera are known from the Amazon River basin of Brazil, Ecuador, Peru, and Venezuela, and the Orinoco River basin of Venezuela. Two species were described in Nemuroglanis, Nemuroglanis lanceolatus, its type species, from the Amazon River, and Nemuroglanis pauciradiatus, from the Orinoco and Negro River basins. Imparales includes its type species, Imparales mariai, from the Orinoco River basin, and Imparales panamensis, from Panama. Medemichthys, also known from Orinoco River basin, is monotypic, with Medemichthys guayaberensis as its type species. Based on the study of morphological characters, we conclude that (1) N. lanceolatus, N. pauciradiatus, and I. mariai constitute a monophyletic group within the Heptapteridae, but I. panamensis is not a member of this clade and is instead part of a currently unresolved clade that includes the genera Chasmocranus, Pariolius, and Phenacorhamdia; (2) N. lanceolatus, N. pauciradiatus, and I. mariai are valid species, but M. guayberensis is a junior synonym of I. mariai; (3) N. lanceolatus and N. pauciradiatus are sister species, and I. mariai is sister to that clade; and (4) the distinctions between I. mariai and the two species of Nemuroglanis render the recognition of both Nemuroglanis and Imparales problematic, prompting us to include I. mariai in an expanded Nemuroglanis. (AU) |