Neotropical monogenoidea. 25. Anacanthorus penilabiatus n. sp. (Dactylogyridae, Anacanthorinae) from Piaractus mesopotamicus (Osteichthyes, Serrasalmidae), cultivated in the State of S？o Paulo, Brazil

anacanthorus penilabiatus n. sp. is described from the serrasalmid fish, piaractus mesopotamicus (holmberg, 1887), cultivated in the centro de aqüicultura, universidade estadual paulista. the new species is characterized by having a relatively straight copulatory organ with a long "lip" on the distal margin and a median longitudinal flap, and a copulatory ligament. the large size of the infrapopulations of this species of parasite indicates that it should be considered a potential agent causing losses in aquaculture of the fish host.