In the present paper the authors describe and illustrate a new species of proteocephalidean cestode, Monticellia belavistensis, sp.n., parasite of a freshwater siluriform fish (thorny catfish). Pterodoras granulosus (Valenciennes, 1833), from the Itaipu Reservoir and Paraná River, in the region of Porto Rico. This is the first reference of a proteocephalid in this host. The values of prevalence and mean intensity of infection are given and the life cycle is discussed.
Proteocephalidea; Monticellia belavistensis; new species; Pterodoras granulosus; Paraná River; Ecology; fish