Approximately 400 specimens of a previously undescribed species of Pseudosonsinotrema sp. (Digenea: Pleurogenidae) were collected from a Paramo marsupial frog, Gastrotheca pseustes (Anura: Hemiphractidae), from the Museo de Zoología of the Pontificia Universidad Católica del Ecuador, Quito, Ecuador. The new digenean species, Pseudosonsinotrema megalorchis n. sp., can be distinguished from others in the genus primarily by its large testes. Flukes attached to the mucosa of the host's intestine cause ulcerative enteritis and become embedded in the intestinal wall, eliciting a severe granulomatous enteritis. This is the first report of this digenean genus from Ecuador and the first report of helminths from G. pseustes. Pseudosonsinotrema saudii is transferred to the genus Pleurogenoides as Pleurogenoides saudii (Ramadan, Banaja, and Saoud, 1980) n. comb. The intense host inflammatory reaction and the relatively low fecundity of specimens suggest that G. pseustes is not the natural host of P. megalorchis.