RESUMO
Leptodactylus paraensis Heyer, is a Neotropical anuran species that inhabits Rainforest habitats in the eastern Amazon, but because it has only been recently separated from the Leptodactylus pentadactylus (Laurenti) species group, little is known about its helminth fauna. This study describes a new species of Oswaldocruzia Travassos, 1917 and records the first occurrence of this genus parasitising L. paraensis and the second species for the Caxiuanã National Forest in the eastern Amazon, Brazil. Oswaldocruzia lanfrediae n. sp. is characterised by having an anterior extremity with a smooth cephalic vesicle divided into two portions, a claviform oesophagus, well-developed cuticular longitudinal ridges and lateral alae. Females have a well-developed ovojector, with didelphic and amphidelphic uteri. Males show complex robust spicules divided into a slightly curved shoe, a bifurcated fork and a blade terminating in 2-3 processes. The new species differs from its congeners especially regarding the lateral alae and the morphology of the spicules, in addition to morphometric characters such as body size, oesophagus length, deirid position, nerve-ring position and relative position of the vulva in females.