A new South American darter (Crenuchidae: Characidium) from rivers draining the Northeastern Mata Atlantica Freshwater Ecoregion, Brazil: morphological and molecular evidence.

Characidium tupi, a new species from rivers draining the southern portion of the Northeastern Mata Atlantica Freshwater Ecoregion, is described. The new species can be distinguished from all congeners by its colour pattern, including 7-14 dark bars enlarged and more conspicuous on their ventralmost portion, resulting in a longitudinal series of conspicuous dark blotches positioned around the midlateral line of the body, and the presence of a conspicuous 3-shaped black band approximately at the midlength of the caudal-fin rays. In addition, the new species differs from most congeners by having a dark band below the midlength of the dorsal-fin rays initiating on the third or fourth branched rays and isthmus, and large areas around the pectoral-fin bases scaleless, but with a broad central patch of scales. Both sexes possess a vestigial swimbladder, which was slightly longer in the males examined. Species delimitation analyses were based on the mitochondrial cytochrome c oxidase subunit I marker and the genetic distances obtained reinforce the recognition of C. tupi as a distinct species, with divergences exceeding 6% in relation to its closely related species.