Priocharax nanus, new species, is described from the rio Negro, Brazil. It is a miniature fish that retains as an adult the larval rayless pectoral fin, a diagnostic character of the genus. Priocharax nanus possesses fewer reductive features compared to congeners, P. ariel and P. pygmaeus, from which it can be distinguished by the presence of i,6 pelvic-fin rays (vs. i,5), the presence of the claustrum (vs. claustrum absent) and the presence of two postcleithra (vs. postcleithra absent). An updated list of 213 species of miniature Neotropical freshwater fishes is presented. The greatest diversity among them is represented by
the Characiformes with 87 miniature species.
Key words: Heterocharacinae, Miniaturization, Reductive characters.
Etymology. The species name is derived from the Latin, nanus, meaning a dwarf and alludes to the tiny size of adult specimens of the species. A noun in apposition.
Mônica Toledo-Piza, George M. T. Mattox and Ralf Britz. 2014. Priocharax nanus, A New Miniature characid from the rio Negro, Amazon basin (Ostariophysi: Characiformes), with an updated list of miniature Neotropical freshwater fishes. Neotropical Ichthyology. 12(2): 229-246. DOI: dx.doi.org/10.1590/1982-0224-20130171 [ufrgs.br/ni]