A new species of the curimatid genus Cyphocharax is described from the Rio Xingu, Amazon basin. This species is readily distinguished from congeners by the presence of a dark, round blotch on the caudal peduncle and by the high density of iridophores on the ventrolateral portion of the body, resulting in a strongly countershaded pattern. Molecular phylogenetic analyses support the recognition of the new species and suggest that it is nested within the Curimatella alburna clade. Ancestral state reconstruction suggests independent evolutionary origins of the blotched caudal peduncle and the countershaded ventrolateral flanks among curimatid fishes.