Revisão taxonômica das espécies de Phenacogaster Eigenmann, 1907 (Ostariophysi: Characiformes: Characidae) da Bacia do Rio Tocantins

Abstract

The Characiformes, which is represented by freshwater fishes of Neotropical and Ethiopian regions, is one of the most diverse orders with more than 1.800 valid species. In this order, 58% of the species belong to the family Characidae. Although several studies have focused on the phylogenetic relationships of Characidae, many of its members do not have a defined phylogenetic position and still have taxonomic issues to be resolved. The genus Phenacogaster is composed of small species, which do not exceed 60 mm standard length and are popularly known as tetra or glasstetra. They are distributed in most river systems of South America, occurring in the basins of the Amazonas, Orinoco, Tocantins, Paraguai, São Francisco, Paraná, coastal rivers of northern and northeastern Brazil and Guyana. The genus has 20 valid nominal species, however, the species of Phenacogaster from the Tocantins basin, an important system with high endemism, have not been properly studied yet. Thus, in order to elucidate taxonomic problems of the genus and to improve our knowledge about the family, this study aims to present a taxonomic revision of the species of Phenacogaster from the Tocantins basin. We also propose updated diagnoses, the description of two new species, the limits of their distributions and a key to the species of that drainage. After examinating 1.194 specimens deposited in Brazilian collections, we conclude that there are five species of Phenacogaster in the basin, which thus are new: the new species Phenacogaster sp. 1 e Phenacogaster sp. 2, both distributed through the upper and middle Tocantins river; P. franciscoensis, originally occurring only in the São Francisco river basin, occurs also in the Tocantins river basin with a wide distribution; P. retropinnus, originally occurring in the Negro, Madeira and Xingu basins, with a new record for the Araguaia river basin; and Complex P. pectinatus, distributed in the lower Tocantins river was here confirmed.