Life cycles of trematodes infecting six species of intertidal gastropods in Japan

A variety of larvae and parthenitae of trematodes have been detected in gastropods in the intertidal zone in Japan. However, because of the difficulty associated with the morphological identification of these stages, they have rarely been identified to the species or higher taxonomic levels. In this study, trematodes of these stages were sampled from intertidal gastropods in the Japanese coastal regions and were identified to the species, genus, or family levels morphologically and molecularly to elucidate or predict their life cycles. Investigation of 17 gastropod species (682 individuals in total) from 14 localities led to the detection of trematodes in 47 individuals belonging to six snail species. The infected gastropods were morphologically identified as <i>Nipponacmea fuscoviridis</i>, <i>Monodonta confusa</i>, <i>Trochus sacellum</i>, <i>Batillaria attramentaria</i>, <i>Littorina brevicula</i>, and <i>Purpuradusta gracilis.</i> Our molecular analyses revealed that sporocysts, rediae, and metacercariae from the gastropods were divided into 14 species belonging to nine families: Philophthalmidae, Fellodistomidae, Gymnophallidae, Lepocreadiidae, Heterophyidae, Opisthorchiidae, Notocotylidae, Microphallidae, and Opecoelidae. These trematodes were thought to use fishes, octopuses, seabirds, and marine mammals as their definitive hosts. Marine organisms such as jellyfishes, crustaceans, and fishes are also thought to act as the second intermediate and paratenic hosts of few present trematode species. As for the other trematode species, DNA barcodes of trematodes from various marine organisms will also illuminate the life cycles in future.