Updated distribution and morphological variation of the genus Pseudanos in the Río de la Plata basin (Characiformes: Anostomidae).

Pseudanos is a fish genus with cis-Andean distribution in South America. Pseudanos trimaculatus is originally known from the Amazon and Orinoco basins. Three decades ago, a few specimens collected in the Río de la Plata basin were identified as P. trimaculatus, what remained to be confirmed and understood. The aim of this contribution is to analyze these specimens. Consequently, the morphological variation of P. trimaculatus is discussed and updated. Morphometric and meristic data were taken from the specimens and compared with those of the type and non-type specimens of the species. Multivariate analyses of the size-corrected measurements were used to explore the morphological variation. Size-corrected PCA revealed that the specimens collected in the Río de la Plata basin nested with the remaining specimens, being slightly closer to those from the Guaporé, Napo and Uatumã rivers. Measurements such as caudal peduncle depth, body depth, and body width affected more heavily the first components. Cluster analysis did not show well-defined groups based on the hydrogeographic basins. The studied specimens from the Río de la Plata basin are herein confirmed as conspecific with P. trimaculatus. The species is added to the list of fish species shared between the Amazon and Río de la Plata basins.

A new species of Ancistrus (Siluriformes: Loricariidae) from Tapajós and Xingu basins, Brazil

A new Ancistrus species is described from Tapajós and Xingu river basins. It is distinguished from its congeners by the singular body color pattern, consisting of dark vermiculated stripes almost all over the body, and also by combination of features as a narrow head, large internostril distance, and absence of rows of enlarged odontodes on the lateral plates. In addition, the new species is distinguished from congeners that inhabit the rio Tapajós basin by the presence of a fully-developed adipose fin (vs. adipose fin absent in Ancistrus parecis and A. tombador, and vestigial adipose fin or absent in A. krenakarore). It differs from A. ranunculus, also from the rio Xingu, by the color pattern, smaller body size, smaller gill opening, and narrower cleithral width. The new taxon adds a new record to the list of species shared among the Xingu and Tapajós basins.(AU)

Uma nova espécie de Ancistrus é descrita das bacias dos rios Tapajós e Xingu. Distingue-se de suas congêneres pelo padrão de colorido único, que consiste em listras vermiculadas escuras em quase todo o corpo, e também pela combinação de características como cabeça estreita, maior distância entre as narinas e ausência de séries de grandes odontódeos nas placas laterais. Adicionalmente, a nova espécie pode ser diferenciada de suas congêneres da bacia do rio Tapajós pela presença de uma nadadeira adiposa totalmente desenvolvida (vs. nadadeira adiposa ausente em Ancistrus parecis e A. tombador, nadadeira adiposa vestigial ou ausente em A. krenakarore). Ela difere de A. ranunculus, a única outra espécie do rio Xingu, pelo padrão de colorido, menor tamanho corporal, menor abertura branquial e menor largura entre os cleitros. O novo táxon adiciona um novo registro à lista de espécies compartilhadas entre as bacias do Xingu e Tapajós.(AU)