Taxonomy of the Terrestrial Crab Geothelphusa tenuimanus (Crustacea: Decapoda: Brachyura: Potamidae) of Okinawa Island, Central Ryukyus, Japan

The Okinawan terrestrial crab Geothelphusa tenuimanus is redescribed and its intraspecific variation is discussed. The geographically isolated Tamagusuku (� southern) population tends to have a more laterally-directed curvature of the anterolateral margins of the carapace and relatively shorter fourth ambulatory legs. However, these differences are not very significant and the diagnostic male first gonopod shows no differences. Therefore, all the populations on Okinawa Island are here regarded as conspecific. Habitats and morphological adaptations of the species are also discussed.