Pomphorhynchus omarsegundoi sp. n. (Acanthocephala:Pomphorhynchidae), parasite of the banded knifefish Gymnotus carapo (Gymnotiformes:Gymnotidae) from the Paraná River basin, Argentina.

Pomphorhynchus omarsegundoi sp. n. from Gymnotus carapo Linnaeus from the Paraná River basin in Argentina is described in this paper. The new species is characterised by having a small body; a non-spirally twisted long neck forming an inconspicuous asymmetrical bulb more developed dorsally than ventrally; a proboscis almost cylindrical, with 11 to 12 longitudinal rows of 5 to 7 (usually 6) hooks each; presence of an apical organ; a mean neck/body ratio of about 1/8; and a post-equatorial male reproductive system, occupying 35-42% of total length. The new species can be easily distinguished from the other four South American pomphorhynchid species by the inconspicuous asymmetrical bulb and the lower number of hooks per row. Pomphorhynchus omarsegundoi is the second acanthocephalan recorded from G. carapo in the Paraná River basin.