Abstract
A new species of the hitherto monotypic bivalve genus Peregrinamor (Galeommatidae) was found attached to the ventral side of the cephalothorax of a small thalassinidean shrimp, Upogebia carinicauda (Stimpson, 1860) (Upogebiidae) collected from tidal flats of Amami-Ohshima Island, Ryukyu Archipelago in Japan. The bivalve is dorso-ventrally flattened and pilfers suspended matter intercepted by the host's filtering basket. This new species, Peregrinamor gastrochaenans, can be discriminated from the type species of the genus, P. ohshimai Shoji, 1938, by its laterally more inflated shell with a permanent postero-ventral gape and by the expanded, fleshy posterior mantle protruding from the gape. Adaptations of the bivalve to the small host species and possible functions of the postero-ventral gape are discussed.
