Drepanotrema kermatoides (Orbigny, 1835) (Mollusca, Planorbidae), hospedeiro de um paranfistomídeo (Trematoda), no Rio Grande do Sul, Brasil

Morphological descriptions and illustrations of the redia, the imature cercaria and mature cercaria, and encysted metacercaria, found in a infected specimen of Drepanotrema kermatoides (Orbigny, 1835) are presented. The infected mollusk was found in Chico Luma creek (29o56'03"S and 50o35'59"W), Santo Antonio County, Rio Grande do Sul State, in May of 1983. These larval stages probably are part of a cycle of a rumen parasite of the genus Paramphistomum (Fischoeder, 1901).