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.

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A new neritiliid species Neritilia mimotoi is described from an anchialine lake on Kamikoshiki Island, Kyushu and estuaries on Shikoku Island, southwestern Japan. This is the second species of the genus described from anchialine habitats. The great variation in shell form and radular morphology of this species has not been previously documented in the family. Anatomical characteristics unique to the species are the presence of a flap-like projection posterior to the left eye and a rudimentary seminal receptacle, both found in females. The egg capsules are reinforced by diatom fragments. They are widely scattered over stones and leaves, as well as laid on shells of other individuals, most frequently on the inner lip callus of males.

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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.

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Two new species of Goniodorididae, one of which belongs to a new genus, have recently been collected from southwestern Japan. They are described in this paper.

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The activity patterns of 9 co-occurring species of molluscan grazers were observed on a gently sloping boulder shore at Amakusa, west Kyushu, Japan. Surveys on their activity were carried out four times in summer : twice during neap tides and twice during spring tides. Snails (Lunella coronata, Nerita japonica and Littorina brevicula) moving on the upper surface of the boulders were considered as 'active', and those not moving but staying on the surface as 'stationary'. With limpets (Nipponacmea concinna, N. nigrans, N. schrenckii, N. teramachii and Patelloida pygmaea) and chitons (Acanthochitona defilippi), all individuals on the upper surface of the boulders were considered as 'active', irrespective of whether they were moving or staying. Interspecific variations related to day/night and tidal conditions were recognized. Two species of snail, N. japonica and L. brevicula, were mainly active when 'emerged' (exposed to air) in the nighttime. Chitons and Nipponacmea limpets were active mainly when 'awash' (affected by wave action) and emerged in the nighttime. L. coronata and P. pygmaea were active in the nighttime irrespective of the tidal conditions. Relationships between the activity patterns and inorganic contents of faeces were observed ; 'limited activity species' (A. defilippi, Nipponacmea spp., L. brevicula and N. japonica), which are active mainly during the 'emerged' and 'awash' conditions in the nighttime, produce faeces of low inorganic content, while 'broad activity species' (P. pygmaea and L. coronata, including Monodonta labio), which are active in the nighttime irrespective of the tidal conditions, produce faeces of high inorganic content. Probably, the 'broad activity species' have more chance to ingest fine inorganic particles accumulated on the surface of boulders during their feeding excursions when submerged than the 'limited activity species'.

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The reproductive cycle and spawning of Modiolus philippinarum were studied in a seagrass bed in Kin Bay, Okinawa Island, southern Japan, based on histological observations of gonads throughout the year. Active gametogenesis occurred in the period from July to October, during which three peaks of spawning were observed at intervals of about 45 days. Drastic declines in water temperature driven by the passing of typhoons were observed several times in the same period. However, the peaks of spawning did not correspond to physical disturbances caused by the passing of typhoons, nor to any particular lunar phase.

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The structures of gonadal tissues of Pisidium (Odhneripisidium) parvum and P. casertanum were studied. In P. (O.) parvum, the testis is located to the right and the ovary is located to the left. P. casertanum has a paired gonad, with both testis located on the outer side and the ovaries located on the inner side. The number of nucleoli in mature oocytes and the shape of sperm heads of both species were different. Ovary activity of P. (O.) parvum increased twice a year in April and August, and testis activity was high in winter.

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Vesicomya kawadai (Aoki) and Calyptogena sp. (Bivalvia : Vesicomyidae) were first obtained from the lower middle Miocene Higashibessho Formation in Toyama Prefecture. This is the oldest record of vesicomyids in the Japan Sea borderland. The Higashibessho Formation at the fossil locality consists of mudstone and alternating beds of sandstone and mudstone which deposited in the bathyal depths of the Hokuriku-Sanin-oki Trough. The deep-sea basin was formed by the early middle Miocene rapid subsidence in relation to the back-arc opening of the Japan Sea. Vesicomya kawadai (Aoki) first occurred from the lower Miocene of the Pacific side and invaded into the Japan Sea just after the formation of the deep-sea basin, maybe together with Calyptogena sp. Both species of vesicomyids may be formed a chemosynthetic community in the deep-sea basin of the Japan Sea.

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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.

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