Endemic land snail fauna (Mollusca) on a remote Peninsula in the Ogasawara Archipelago, northwestern Pacific

摘要

Historically, the Ogasawara Archipelago harbored more than 90 native land snail species, 90 of which were endemic. Unfortunately, about 40 of the species have already gone extinct across the entire archipelago. On Hahajima, the second-largest island and the one on which the greatest number of species was recorded, more than 50 of species are thought to have been lost. We report here the results of a recent survey of the snails of a remote peninsula, Higashizaki, on the eastern coast of Hahajima. Although the peninsula is small (similar to 0.3 km(2)) and only part is covered by forest (< 0.1 km(2)), we found 12 land snail species, all of which are endemic to Ogasawara. Among these species, five had been thought to already be extinct on Hahajima, including Ogasawarana yoshiwarana and Hirasea acutissima. Of the former, there has been no record since its original description in 1902. Except for the much larger island of Anijima and the main part of Hahajima, no single region on the Ogasawara Archipelago maintains as great a number of native land snail species. It is probable that the land snail fauna of the Higashizaki Peninsula is exceptionally well preserved because of a lack of anthropogenic disturbance and introduced species. In some circumstances, even an extremely small area can be an important and effective refuge for threatened land snail faunas.