lymnaeidae are of major medical and veterinary importance since they act as vectors of parasites (helminths, mainly trematodes, e.g., "fasciola" liver flukes) that severely affect human populations and livestock, and cause important economic losses. lymnaeids serve as intermediate hosts of at least 71 trematode species distributed among 13 families, including some species of schistosomatidae and echinostomatidae, with implications for human health, and "paramphistomum daubneyi", which is of veterinary interest. the most emblematic case of parasite transmitted by lymnaeids is "fasciola hepatica" (digenea: fasciolidae), the agent of fascioliasis. mollusks, generally lymnaeids, are required as intermediate hosts to complete the life cycle of "fasciola hepatica". at least 20 species of lymnaeidae have been described as potential vectors of fascioliasis.