Abstract
Characidium nana is described from the Rio Xingu and Rio Tapajós drainages. The new species is distinguished from all its congeners by the absence of the inner series of dentary teeth, the absence of the parietal branch of the supraorbital laterosensory canal, the incomplete lateral line, the lack of an adipose fin, the presence of a conspicuous dark blotch on caudal peduncle as well as an evident dark, midlateral stripe, and the presence of 12 circumpeduncular scales. The relationships of the new species and its inclusion among the species of clade C4 are discussed.