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Keywords:Brachylaima ezohelicis sp. nov. Ezohelix gainesiHokkaido -3 - IntroductionLand snails are terrestrial gastropod mollusks with or without shells, and the majority are hermaphroditic pulmonates. They have been highly diversified in the Japanese Archipelago, and the resulting fauna now includes approximately 800 species in spite of its small land area [Biodiversity Center of Japan (biodic.go.jp)]. Many of them are endemic species to Japan. Such a unique situation provides advantages to study evolutionary ecology in a geographic context. However, there have been few studies done concerning host-parasite ecological relationships between Japanese land snails and their internal organisms.As concerns trematode parasites, members of the families Brachylaimidae In this study, a small number of immature brachylaimids were found from intestines of Japanese toads (Bufo japonicus formosus) captured in a forest city park in Asahikawa, Hokkaido, the northernmost island of Japan. The infection seems to be accidental because the gravid adult worms were never seen in the other toad samples. The toad is an alien species from the Kanto region of Honshu island where there are no records of brachylaimid infections in amphibians [20]. A subsequent snail survey in the city park showed that land snails of Ezohelix gainesi (Bradybaenidae) are heavily infected with both sporocysts and metacercariae. A DNA sequence identification revealed that all the immature parasites detected from the toads and the snails belong to the same species. Fully matured adults were obtained through an experimental infection of immunosuppressed mice with metacercariae from E. gainesi. Based on morphological features of the adult specimens, we propose a new species of the genus Brachylaima. In this study, an additional description of Brachylaima sp., which has already been reported from the large Japanese field mouse Apodemus specious in Hokkaido [14], was also made for comparison with the new species.

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