RESUMO
Myleus pachyodus, a new serrasalmid species, is described from the Rio Teles Pires and Rio Jamanxim, both tributaries of the Rio Tapajós in Mato Grosso and Pará states, Brazil. The new species differs from all congeners by having a remarkable ontogenetic thickening of the teeth shifting from slender incisiform in juveniles to thick bulky teeth at standard length ≥ 100 mm, whereas congeners present slender, antero-posteriorly flat teeth throughout all life stages. The new species further differs from congeners by having 18-20 branched dorsal-fin rays, by the lack of a diastema between contralateral outer series of premaxillary teeth and by the presence of 16-25 prepelvic spines, with the anteriormost spine never reaching the vertical through the pectoral-fin origin.
Assuntos
Caraciformes/anatomia & histologia , Caraciformes/classificação , Animais , Biodiversidade , Brasil , Conservação dos Recursos Naturais , Feminino , Masculino , Pigmentação , Rios , Caracteres Sexuais , Dente/anatomia & histologiaRESUMO
Two new species of Tometes from the Brazilian Shield rapids are described. Tometes kranponhah is endemic to the Xingu River basin, whereas Tometes ancylorhynchus occurs both in the Xingu and the Tocantins-Araguaia River basins. The two species are sympatric in the Xingu drainages and have many similarities in morphology and colouration. Major diagnostic differences are the dark pigmentation on the opercle of T. kranponhah and its distinct snout shape and arrangement of premaxillary teeth. In addition, T. kranponhah is a large fish that is abundant in the Xingu River, whereas T. ancylorhynchus is a medium-sized fish for which there are few records.