New species of bumblebee catfish of the genus Batrochoglanis Gill, 1858 (Siluriformes: Pseudopimelodidae) from the Aripuanã River basin, Mato Grosso, Brazil.

A new species, Batrochoglanis castaneus, is described from the Aripuanã River basin, Brazil. It differs from congeners, except B. raninus and B. transmontanus, by the dark brown color of the body and a dark brown stripe on the caudal fin. The new species differs from B. raninus by the longer maxillary barbel, longer prepelvic length, greater prepectoral length, smaller anal-fin base length, and smaller head depth. The new species differs from B. transmontanus by the longer caudal-fin dorsal lobe, presence of a hyaline spot or stripe on pelvic, dorsal, and anal fins, longer maxillary barbel, longer pectoral-fin, and dorsal-fin spines, greater eye diameter, smaller head depth, and larger mouth width. A metapterygoid anteriorly bifurcated and the lateral line reaching the adipose fin present in the new species are interpreted as synapomorphies of Batrochoglanis. On the other hand, the distribution of pore and neuromasts of the laterosensory system of the head seems to be very conservative in the family. The new species is known only from the Aripuanã River basin, reinforcing its characteristics as an area of endemism for fishes in the Amazon basin.