Abstract
Distribution pattern of the porcelain crab, Petrolisthes japonicus found in the intertidal boulder beaches of an oceanic island, Chichijima, Ogasawara (Bonin) was compared with that in a continental island, Zamami, Okinawa (Ryukyu). P. japonicus occupied widely over the entire intertidal boulder beaches in Ogasawara, where only one species of the porcelain crab inhabits. In Okinawa, however, P. japonicus was restricted in the middle intertidal zone and its habitat was significantly narrower and higher than those on Chichijima. In Okinawa, six other species of porcelain crabs, P. hastatus. P. lamarckii, P. fimbriatus, P. tomentosus, P. carinipes and P, asiaticus coexisted there, and the distribution patterns of them can be clearly divided into two types: the middle intertidal type, (P. japonicus and P. hastatus) and the lower intertidal type (P. asiaticus, P. tomentosus, P. lamarckii. P, fimbriatus and P. carinipes.
