Morphology and molecular evidence of a new species of <i>Characidium</i> (<scp>Characiformes: Crenuchidae</scp>) from the edges of a protected area at <scp>Rio Itararé</scp>, upper <scp>Rio Paraná</scp>, southern <scp>Brazil</scp>

A new species of Characidium is described from the headwaters of the Rio Itararé, upper Rio Paraná basin, at the boundaries of the Ponta Grossa Arch and the Devonian Escarpment Environmental Protection Area. The new species is supported by both morphological and molecular data, including species delimitation methods (Assemble Species by Automatic Partitioning, Barcode Index Number, Poisson Tree Process and its Bayesian implementation, and Generalized Mixed Yule Coalescent). The species is genetically close to other species that also exhibit the presence of scales on the isthmus, including Characidium litorale, Characidium satoi, Characidium xanthopterum, and Characidium aff. zebra. The high genetic diversity among Characidium species underscores the necessity of employing a complementary perspective in studies of this group. The discovery of a new species in the headwaters of the Rio Itararé further reinforces the importance of this biogeographic region for the conservation of ichthyofauna.