A new species of Characidium (Characiformes: Crenuchidae) from the Iguaçu National Park, Rio Iguaçu basin, Paraná, Brazil.

A new species of Characidium is described from the Iguaçu National Park, Brazil. The new species can be diagnosed from the congeners by the absence of conspicuous vertical bars, blotches and spots along the sides of the body, the presence of a scaled isthmus and adipose fin, a series of scales below lateral line and the presence of a thin dark midlateral stripe. The reticulated colour pattern of melanophores along the posterior edge of scales found in the new species is similar to that found in C. xanthopterum, with which it presents 4.2% of genetic distance. Morphological and molecular analyses showed that it is a new species, supported by multiple species delimitation methods (Assemble Species by Automatic Partitioning, the General Mixed Yule Coalescent method, and the Poisson Tree Process and its Bayesian implementation). The new species is a sister group of C. itarare, a species that occurs in the Paranapanema river basin (upper Paraná river). Despite being located within a conservation unit, the new species is known from only two creeks, raising concerns about its long-term conservation.