A new species of Diapoma (Characiformes, Characidae, Stevardiinae) from the Rio Paraná basin, with an identification key to the species of the genus

Diapoma nandi is described from the Piray‐Miní stream, a tributary of the Rio Paraná in Argentina. It is characterized among the Stevardiinae by having a terminal mouth, two unbranched and eight branched dorsal‐fin rays, one unbranched and six branched pelvic‐fin rays and the absence of a caudal‐fin organ and is distinguished from all congeners by the following combination of characters: unmodified scales on the lower caudal‐fin lobe, lack of enlarged opercle and subopercle, incomplete lateral line, hyaline adipose fin, anal‐fin distal border straight or slightly convex in adult males, large tricuspid teeth on anterior region of the dentary, distal arrangements of the anal‐fin bony hooks in adult males, middle caudal‐fin rays lacking large round blotch and several morphometric variables associated with body shape. Additionally, we conducted a morphometric comparison focused on the congeners that co‐occur in the Paraná basin.