Three species of Planorbidae have been reported from Korea, e.g., Gyraulus convexiusculus, Hippeutis (Helicorbis) cantori, and Segmentina (Polypylis) hemisphaerula. Of these, only H. cantori was reported as the first and second intermediate host for Echinostoma cinetorchis, an important human intestinal parasite in Korea. Segmentina hemisphaerula has also been found to be an intermediate host. In field-collected planorbids, only S. hemisphaerula was found shedding echinostome cercariae and infected with metacercariae of E. cinetorchis, whereas no G. convexiusculus and H. cantori were found to be infected. In experiments with laboratory-bred snails, G. convexiusculus and S. hemisphaerula were susceptible to infection by miracidia of E. cinetorchis, but H. cantori could not be infected. Tadpoles of Rana nigromaculata and laboratory-bred snails of the 3 planorbid species were exposed to E. cinetorchis cercariae shed from field-collected S. hemisphaerula. All tadpoles, S. hemisphaerula, and G. convexiusculus became infected, but no H. cantori were infected. Metacercariae from tadpoles, S. hemisphaerula, and G. convexiusculus were fed to rats per os, and eggs of E. cinetorchis were detected in the rat feces 1 wk later. The rats were killed, and adult E. cinetorchis were recovered from the small intestines. This is the first report of G. convexiusculus as a potential first and second intermediate host and of S. hemisphaerula as a new first and second intermediate host for E. cinetorchis in Korea.

Three species of freshwater pulmonate snails of Lymnaeidae have been reported from Korea, Radix auricularia coreana, Austropeplea ollula, and Fossaria truncatula. Of these 3 species, only A. ollula was naturally infected with Neodiplostomum seoulense cercariae (prevalence, 0.3%). In experiments with the laboratory-reared snails, A. ollula was found to be susceptible to the N. seoulense miracidia (prevalence, 10%). This is the first report of A. ollula as the first molluscan intermediate host for N. seoulense in Korea.