Geothelphusa miyakoensis, a new species of freshwater crab (Crustacea: Decapoda: Brachyura: Potamidae) from Miyako Island, Southern Ryukyus, Japan.

Geothelphusa miyakoensis, new species, from Miyako Island, Southern Ryukyus, Japan, is described. The new species is closest to G. levicervix (Rathbun, 1898) (sensu Minei, 1973), but is distinguished by a number of characters of carapace, male abdomen, first gonopod, cheliped, and second ambulatory leg. The new species is also similar to the Taiwanese G. bicolor Shy, Ng & Yu, 1994, G. caesia Shy, Ng & Yu, 1994, and G. yangmingshan Shy, Ng & Yu, 1994, but differs in characters of the carapace, first gonopod, male abdomen, ambulatory legs, and colour. The present work is the first finding of potamid crab from Miyako Island, and brings the total number of Geothelphusa species known to 42.