Four new species of the family Turbinidae and two new species of the family Trochidae all collected from bathyal depths and seamount in Japanese waters are described : Homalopoma bicolor, Cantrainea nuda, Bolma myrica, Liotina montamarina, Monilea cocoa, and Prothalotia boninensis.
A new species, Bathymodiolus marisindicus n. sp., is described based on specimens collected at a hydrothermal vent site in the Indian Ocean. This new species differs from B. thermophilus by the absence of the inner mantle fusion and a very short valvular siphonal membrane. Bathymodiolus marisindicus n. sp. resembles B. septemdierum and B. brevior from the western Pacific Ocean. However, it is distinguishable from these species by the height/length ratio, the length and strength of the ligament, the positions of the anterior retractor muscle scar and the anterior bundle scar of posterior byssal retractor muscle, the thickness of the pedal retractor muscle and by the shape of the intestine.
Seasonal changes in the distribution and mating behavior of the potamidid snail Cerithidea rhizophorarum A. Adams, 1855 were investigated on a tidal flat in the Atago River, Kyushu, the most northern mangrove forest in the world. Two potamidid species, Cerithideopsilla djadjariensis (K. Martin, 1899), and Cerithideopsilla cingulata (Gmelin, 1791), and one batillarid species Batillaria multiformis (Lischke, 1869) co-occurred with C. rhizophorarum in this area. Newly-recruited juveniles (3-6 mm shell width) of C. rhizophorarum appeared from November to March. Adults of C. rhizophorarum were found in higher tidal zones than the other potamidid and batillarid species. The distribution of juveniles of C. rhizophorarum, however, was limited to lower tidal zones. Copulating behavior was observed at daytime low tide from June to August. Courtship behavior of C. rhizophorarum follows a fixed pattern. First, one animal (the initiator) approaches another and mounts its shell. If the lower animal (the acceptor) accepts the courtship, the upper animal (the initiator) inserts its soft body into the body of the lower animal. In about 80 % of copulatory pairs, the upper animals were male and the lower ones female. However, male to male copulation accounted for about 20 % of copulatory pairs. Copulation lasted for 11 to 74 minutes (mean : 20 minutes). Mating of C. rhizophorarum was random with respect to shell size.