A new species of Hedruris Nitzsch, 1821 (Nematoda: Hedruridae) parasitic in the freshwater fish Oligosarcus jenynsii (Günther, 1864) (Characidae) from Argentina.

Nematodes belonging to genus Hedruris Nitzsch, 1821 (Nematoda: Hedruridae) were found in the stomach of the freshwater fish Oligosarcus jenynsii (Günther, 1864) (Characidae) from a shallow eutrophic lake in Argentina. Morphological comparisons with congeneric relatives showed that these nematodes belong to a new species, for which H. bifida n. sp. is proposed. Hedruris bifida n. sp. can be distinguished from its congeners by the following combination of characters: bifid deirids, absence of precloacal papillae and nine pairs of postcloacal papillae and non-mammillated eggs. The new species closely resembles Hedruris suttonae Brugni & Viozzi, 2010¸ the only known species from Argentina; however, the bifid deirids in the new species and the distribution pattern of perianal spines in females clearly distinguish both species. Hedruris bifida n. sp. represents the second nominal species of the genus in Argentina and the eighth species described in the Neotropical region.