Abstract
A new species of bopyrid isopod, Probopyrus iriomotensis sp. nov. parasitizing palaemonid freshwater shrimps of the genus Macrobrachium, is described based on material from Iriomote Island, Ryukyu Islands, southwestern Japan. The new species most commonly infects the branchial chambers of Macrobrachium shokitai Fujino and Baba, 1973, but rarely also M.formosense (Bate, 1868). The new species is similar to Probopyrus ascendens (Semper, 1880), P.gangeticus Chopra, 1923, and P.giardi Weber, 1892, but can be distinguished from them by a combination of characters of the pleomere and pleotelson, relative body width, and the degree of deflection of the body axis. This is the first species of Bopyridae to be recorded from a freshwater environment in Japan. In addition, the generic assignment of two marine species of Probopyrus is questioned, and the date of authorship of P.marinus Nierstrasz and Brender a Brandis, 1923 is clarified.
