3Departamento de Parasitologia Animal, Universidade Federal Rural do Rio de Janeiro,

205 Species of Prochilodus Agassiz 1829 are among the most abundant fishes of South America basins and has good potential for pisciculture. During a study of the helminth parasites of Prochilodus lineatus (Valenciennes, 1837) (Characiformes) from Mogi Guaçu River, Brazil, a new species of Tereancistrum was collected. Tereancistrum pirassununguensis n. sp. can be distinguished from the other Tereancistrium species mainly by having a reduced accessory anchor sclerite with a little groove at the end; MCO as a sclerotized coiled tube forming two counterclockwise rings; an accessory piece as an inverted C, rod-like, not articulated at the base of the MCO; curved ventral bar; hooks similar with erect thumb and slightly curved shaft and point, slightly expanded shank proximally. This is th