A new vesicomyid bivalve, Calyptogena solidissima is described from the Minami-Ensei Knoll, west of the Amami-Oshima Island, where hydrothermal vents were discovered. C. solidissima n. sp. is close to C. soyoae in general appearance, but it is characterized in having a robust shell with very fine radiated threads, straight ventral margin and subumbonal pit.

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Among the gastropod specimens trawled from bathyal depths (450-780m) 18 species were identified. Four species, namely, Eosipho tosaensis, Neptunea kotakamaruae, Antiplanes delicatus, and Spergo nipponensis are recognized to be new species. Morphological characters, particularly radula, and distributions of "rare" species, e.g. Otukaia kiheiziebisu, Orectospira tectiformis, Trophonopsis soyoae, Buccinum koshikinum, Ptychosirynx bisinuata japonica among others are discussed. Bathyal gastropod fauna in Tosa Bay seems to represent a mixture of faunulae of intermediate (slope) water and undercurrent.

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Distribution and movement of Littoraria intermedia, L. scabra, and L. pallescens were investigated in the Fukido Mangal and on the coast of Miyara Bay on Ishigaki Island, Okinawa, southern Japan. Significant differences were detected between these three species in their vertical distribution, distribution on different mangrove trees, distribution on different kinds of substratum on the trees, and density on a concrete wall, but differences were not in most cases found between the two color types of L. pallescens. Obvious differences were also found between L. intermedia and L. pallescens in their patterns of vertical movement related to tide, and in their locomotive activity in rain. These ecological characteristics are consistent with the taxonomic scheme of mangrove littorinids by Reid (1986), and provides preliminary data on the diversification of littorinids in mangrove swamps.

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Seasonal changes in gametogenic activity and embryo composition in the brood pouch of the ovoviviparous freshwater prosobranch Semisulcospira libertina (Gould) were studied on the specimens collected bimonthly during a year from two different habitats in Gunma Prefecture, i. e., a channel for agriculture located at Hikita of Fujimi village at the foot of Mt. Akagi where water temperature shows fairly distinct seasonal changes and a fishpond in Hakoshima of Azuma village at the northern foot of Mt. Haruna where water temperature remains almost constant throughout the year. Histological observations on the testes revealed that in males from Hikita spermatogenesis was active from spring to summer when water temperature rises gradually, but in males from Hakoshima spermatogenesis occurred throughout the year. These results indicate that spermatogenesis is influenced by water temperature, that is, it begins with the rise of water temperature, it becomes inactive with the fall of water temperature, and it occurs continuously when water temperature is constant although it is low as at about 14℃. In all the males from both habitats, mature spermatozoa were contained in the vas deferens throughout the year. Histological observations on the ovaries indicated that oogenesis is also influenced by water temperature. In females from Hikita, oogenesis begins active from spring to summer when water temperature rises. But it does not show distinct seasonal changes as in the spermatogenesis, and occurs throughout the year with varying activities. On the other hand, in females from Hakoshima, oogenesis occurred throughout the year showing the largest development of the ovaries in March. The number of embryos in the brood pouch showed a tendency to increase with the size of mother shell, but showed a great individual variation. Snails from Hikita were larger in shell size than those from Hakoshima, having generally many embryos. In females from Hikita, the total number of embryos in each brood pouch was largest in February, having many late shelled-embryos but few early embryos. The total number of embryos decreased thereafter becoming smallest in August, but the number of early embryos was largest in August. From autumn to winter late shelled-embryos increased with the increase of total number of embryos. In Hakoshima, the total number of embryos was largest in March and smallest in September, but showed no distinct seasonal tendency. As to the embryo composition in females of this habitat, early embryos accounted for about 50% constantly throughout the year. In conclusion, it was considered that gametogenesis and embryonic development are greatly influenced by the change of water temperature. Increasing water temperature from spring to summer activates spermatogenesis and oogenesis as well as production of embryos and birth of newborns.

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The giant African snail, Achatina fulica (Ferussac), was introduced into and is now abundant in Ryukyu and Ogasawara Islands, Japan. Its clutch size varied from 13 to 137, and egg volume from 35 to 85 mm^3. There was no significant difference in clutch size or egg volume by season and by locality. The clutch size and egg volume were positively correlated with the shell lengths of parents. Snails with reproductive organs were divided into three age groups ; viz. "young-adult", "intermediate", and "old-adult", according to degree of peristome thickness. No "young-adult" had eggs. The "old-adult" produced larger clutches and eggs than the others. It was concluded that A. fulica had a great variability in reproductive performance.

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Infection experiment of the glochidium of a freshwater pearl mussel, Hyriopsis (Limnoscapha) myersiana in 11 species' of fish was carried out, using 4 levels of glochidia concentration. The mortality of the fish after infection was plotted against these exposure levels. After 30-days, the interpolated LE_<50> values (exposure concentration of glochidia that killed 50% of the fry) for Iridescent mystus (Mystus vittatus), Striped catfish (Pangasius sutchi), and Yellow mystus (M. nemurus), were 15, 000, 20, 000, and 50, 000, respectively. The mortalities were very low in Striped tiger nandid (Pristolepis fasciatus) and Temminck's kissing gourami (Helostoma temmincki). The most resistant were Sand goby (Oxyeleotris marmoratus) and Striped tiger nandid (Pristolepis fasciatus), which also gave the highest production of juveniles. Species of Rasbora were not resistant at all, and all specimens died soon after infection.

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Antigenic structures of Brazilian species of Biomphalaria glabrata pigmentado, B. glabrata albino and B. straminea were compared using immunoelectrophoresis. The results obtained were summarized as follows ; 1) In the cases of immunization with Biomphalaria snails, 22-23 precipitin bands were observed between the antigens and its homologous antisera, and 15-20 bands were showed in the heterologous reactions. 2) The common antigenicities between B. glabrata pigmentado and B. glabrata albino were proved to be more than that between B. glabrata pigmentado and B. straminea, and that between B. glabrata albino and B. straminea. 3) Some residual bands were observed by absorption procedure showed different patterns of immunoelectrophoretic bands.

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Copulation frequency and mating system of the simultaneously hermaphroditic land snail Acusta despecta sieboldiana (Pfeiffer) were observed under the laboratory condition. Mode of copulation was considered to be the simultaneously reciprocal type. Copulation was first observed on late March, 250 days after the hatching, and continued till early December. The frequency of copulation was highest in April. The snails randomly copulated with each other, and there was no significant difference in either choice of the partner or size correlation between the pairs, although the theory of evolutionary ecology has predicted that the size homogamy should be seen between pairs in simultaneously hermaphroditic species.

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