Crepidula fornicata is not a first intermediate host for trematodes: who is?

Trematode larvae must generally invade a molluscan intermediate host, usual ly a gastropod, before they can reach reproductive maturity in another defi nitive host. The research literature to date has focused almost exclusively on the documented specificity between particular trematode species and par ticular molluscan hosts; little attention has been paid to gastropod specie s that do not appear to serve as hosts. We sampled Rhode Island and Massach usetts populations of the marine gastropod Crepidula fornicata to determine whether this widespread species serves as a first intermediate host for tr ematodes. We also sampled from the same habitat populations of Littorina li ttorea and Ilyanassa obsoleta, gastropods known to serve as first intermedi ate hosts for several trematode species. All individuals were examined by d issection for the presence of sporocysts, rediae, or developing cercariae. Although 4-28% of L. littorea (N = 112) and I. obsoleta (N = 84) were infec ted by larvae of at least one trematode species, no individuals of C. forni cata sampled from the same locations were so infected (N = 136). A survey o f the Biological Abstracts computer database indicates that snails in only about 10% of marine gastropod families are known to serve as first intermed iate hosts for trematodes. We suggest that more attention be paid to marine gastropods that appear not tu be infected by trematode miracidia. Such spe cies may productively serve as new models for understanding trematode host specificity and gastropod resistance to infection. (C) 2001 Elsevier Scienc e B.V. All rights reserved.