Cnesterodon pirai Aguilera, Mirande & Azpelicueta 2009

Cnesterodon pirai is diagnosed by the combination of the following characters: 6 to 8 irregular dashes on flanks, ranging from oval to vertical stripes on females and 7 to 9 irregular dashes ranging from oval to circular dots on males (dashes both on males and females covering 1 or 2 scales in transverse row); absence of a large post-gonopodium blotch on ventral profile in adult males; lack of a distal filament ongonopodium; absence of longitudinal dark-brown band along flank; snout pointed and long (16.7–28.7 %HL); possession of 12–13 epipleural ribs; medial surface of ascending process of premaxilla approximately straight; presence of teeth on fourth ceratobranchial; distal portion of third and fourth gonactinosts separate, except by tip of third gonactinost; fifth gonactinost free; and presence of a constriction on unpaired appendix of gonopodium (Ref. 82179).

The stream where the new species lives is narrow (2 m wide on its widest section) and shallow, with falls about 80 cm depth, and moderately slow current. It is a tributary of the Cuña-Pirú stream (above Salto Encantado, a fall with 40 m depth); the creek only has 700 m from its headwaters to the confluence with Cuñá-Pirú. The rocky stream bed, covered by detritus over 50% of its surface, presents small pools and glides. Cnesterodon pirai was especially found forming schools of juveniles and adults in pools (Ref. 82179).