A new genus and species of South American fishes (Teleostei : Characidae :Cheirodontinae) with a derived caudal fin, including comments about inseminating cheirodontines

Acinocheriodon melanogramma from tributaries of the rio Sao Francisco and t he rio Jequitinhonha, Minas Gerais, Brazil, is described as a new genus and species of inseminating cheirodontines. The adult males are distinguished by possession of modified thirteenth to fifteenth, ventral caudalfin rays b earing dorsally directed hooks surrounded by fleshy, possibly glandular, st ructures. These structures appear similar to, but are here hypothesized as convergent with some of the derived caudal glandular organs of certain glan dulocaudine characids and the species of the incertae sedis characid genus Brittanichthys. Putative relationships of these taxa to the new genus are e xplored and rejected. The new species is referred to the Cheirodontinae on the basis of a cladistic diagnosis of this subfamily. Hypotheses of relatio nships with other inseminating cheirodontines bearing modified caudal fins are explored.