Although it is commonly assumed that all gastropod species serve as hosts for larval stages of one or more trematode species, the marine gastropod Crepidula fornicata seems not to serve as such a host. In this study, we sampled populations of the related species Crepidula plana and Crepidula convexa from Rhode Island and Massachusetts, U.S.A., to determine if any individuals served as hosts for larval trematodes. No signs of parasitic infection were found, although up to 14% of co-occurring periwinkles (Littorina littorea) were so infected. Although most research has focused on known associations between larval trematodes and their gastropod hosts, we suggest that additional work focus on understanding why some gastropod species seem immune, or at least relatively immune, to infection by larval trematodes.