RESUMO
A new species of Spectracanthicus is described from the Rio Javaés, Rio Araguaia basin. The new species is distinguished from its congeners (except Spectracanthicus immaculatus) by colour pattern: body dark grey to dark brown without dots or blotches (v. body colour with yellowish small dots in Spectracanthicus murinus, Spectracanthicus punctatissimus and Spectracanthicus tocantinensis and large white dots in Spectracanthicus zuanoni). It can be further distinguished from S. immaculatus by having thicker and less numerous teeth, with up to eight premaxillary and 20 dentary teeth (v. teeth thinner and more numerous with up to 22 premaxillary and 30 dentary teeth); dorsal and caudal fins without curved spines (v. dorsal and caudal fins with curved spines). Other osteological characters can also diagnose the new species from its congeners. In addition, a gross brain description and brief comments on the new species' ecological habitat are given.
Assuntos
Encéfalo/anatomia & histologia , Peixes-Gato/anatomia & histologia , Animais , Biodiversidade , Brasil , Cor , Ecossistema , DenteRESUMO
New data are presented on the sex chromosomes of the fish species Eigenmannia virescens (Gymnotiformes, Sternopygidae). A new finding, involving the occurrence of ZZ/ZW sex chromosomes, is described in specimens sampled from the São Francisco and Amazon river basins in Brazil. All individuals had a chromosome number of 2n = 38. The homologs of the sex chromosome pair from the São Francisco river basin sample differed only in their morphology, while those from the Amazonian sample differed both in morphology and heterochromatin pattern. A possible model for the evolution of the sex chromosomes in E. virescens is proposed, including data from populations from the Paraná (Brazil) river basin, in which male heterogamety has already been described. The occurrence of different sex chromosome systems in species and populations of the neotropical freshwater fish fauna is discussed.