Kritskyia annakohnae n. sp. (Dactylogyridae, Ancyrocephalinae) is described from the ureters and urinary bladder of the piranhas, Serrasalmus marginatus Valenciennes, 1836 and S. spilopleura Kner, 1858 (Characiformes, Serrasalmidae) from the Rio Baia, Paraná, Brazil. The new species is characterized by having a keel-like projection on the left margin of the trunk and an accessory piece comprising two parallel subunits, proximally and distally fused. An emended diagnosis of Kritskyia Kohn, 1990 is provided to accommodate the new species. Although previously suggested, Kritskyia is probably not closely related to other Dactylogyridae lacking haptoral anchors and bars. Present knowledge on morphology and phylogeny indicates that the loss of these sclerites has occurred independently several times within the family.
Platyhelminthes, Monogenea, Monogenoidea, Dactylogyridae, Ancyrocephalinae, Kritskyia, Kritskyia annakohnae n. sp., Teleostei, Serrasalmidae, Serrasalmus marginatus, Serrasalmus spilopleura, Rio Baia, Paraná, Brazil, new species, parasitology.