A new genus and species of small characid (Ostariophysi, Characidae) from the upper rio Bermejo basin, northwestern Argentina

A new genus and species of small characid is described in this paper. The new genus, Nans gen. n., is diagnosed by the combination of: ii,7-8 dorsal-fin rays, 10-15 branched anal-fin rays, 5 teeth in the inner premaxillary row, rotation of the pelvic bone about 90degrees, rotation of the pelvic fin muscles, pelvic fin curved and forming a complete tube in mature males, incomplete foramen for exit of the olfactory nerve in the lateral ethmoid. Other characters which help in the identification of Nans are the large subcircular foramen in the dorsal vomerine lamella which articulates with the mesethmoid, the absence of an extrascapular sensory canal in the postemporal, and a laterosensory canal in the anguloarticular. The type species, Nans inde-fessus sp. n. was collected in the rio Anta Muerta and arroyo Colorado, tributaries of the rio Blanco, and in the rio Pescado, upper rio Bermejo basin, Salta, Argentina.