Four new species of Bathymodiolus, B. platifrons n. sp., B. japonicus n. sp., B. aduloides n. sp., and B. septemdierum n. sp., are described from materials collected at hydrothermal vent and cold seep sites around Japan. These deepsea mussels have extremely thick and large ctenidia with long demibranchs. In addition, these new species have no extreme mantle fusion which restricts the incurrent aperture to a short byssal-pedal gape in the ventral mid-region, the typical feature of the genus Bathymodiolus Kenk and Wilson, 1985.

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Intra- and interspecific variation in activity patterns of intertidal limpets was analysed focusing on the relationship between level of activity and height of their resting sites under several tidal conditions. At a study site in the upper intertidal zone where night emersion occurred, two species resting highter on the shore tended to be more active during the night emersion than two other species resting lower on the shore. In regard to all ten groups of six species at three study sites covering the upper to lower intertidal zones as a whole, level of activity during the daytime submersion was negatively correlated with height of their resting sites ; lower zone-dwelling limpets were more active than upward-dwelling limpets during the period. Among four groups of Cellana toreuma inhabiting the mid to lower shores, lower populations showed greater activity than upper populations during the day and night submersion. These results were obtained both at spring and neap tides, and causes of this variation are discussed in relation to vertical gradients in intensity of desiccation and predation.

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Reproduction was studied for the neptune whelk Neptunea arthritica in Lagoon Saroma. Fishery of the whelk has been prohibited in the lagoon since 1986 because of depleting resource, however, only few egg masses were observed. Histological examination and gonado-somatic index (GSI) showed the distinct annual reproductive cycle. The cycle is as follows : in ovaries, recovery period (Aug.-Nov.), growing period (Oct.-Apr.), mature period (Apr.-July) and spent period (May-Aug.) : in testes, recovery period (Apr.-May), growing period (Apr.-July), mature period (Aug.-Dec.) and spent period (Nov.-Apr.) : in seminal vesicles, resting period (July-Aug.), accumulating period (Sep.-Apr.) and spent period (Apr.-June). Copulating and spawning periods were from April to August and from May to August, respectively. Whelks infected by digenean trematodes were observed in the lagoon. GSI and histological feature in infected and uninfected females were different. Infected females could not develop the ovaries. Infected males also showed lower values in both testis and seminal vesicle indexes, although their annual trends were similar to that of uninfected males. Influence of parasites on the females was stronger than on the males. Because the infection rate of the whole area was very low and GSI value was high even after spawning time in the place where infection rate was low, infection of parasites was not the main factor which prevented the neptune whelk from spawning in the lagoon.

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The two forms of Thais clavigera (Forms C and P) differ morphologically and ecologically. Form C grows larger than Form P. Form C change diets from the small barnacle Chthamalus challengeri to larger prey such as Tetraclita squamosa japonica as they grow while Form P exclusively prey upon Chthamalus challengeri irrespective of their sizes. To know whether the differences in growth and prey preference between the two forms are based on their genetic differences, small individuals of both forms, which seem to have feed mostly upon C. challengeri in the field, were reared on several prey conditions for 10 months. Growth and feeding rates of Form C were larger than those of Form P during rearing irrespective of prey species given. Individuals of Form C and Form P reared with a single prey species selected that prey more frequently than those reared with other prey species in the prey selection experiment conducted after 10 months rearing, but Form P always preferred C. challengeri more strongly than Form C as in the field. The differences in growth and prey preference between the two forms were thus suggested to reflect some genetic difference between them.

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The two genera with two subgenera each are recognized for the squid family Mastigoteuthidae. The genus Mastigoteuthis contains two subgenera, Mastigoteuthis s. str. and Echinoteuthis. The genus Idioteuthis is here resurected, and it is divisible into two subgenera, Idioteuthis s. str. and Magnoteuthis nov.

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Holotype specimens of four lottiid species described from Hong Kong by Christiaens (1980) are illustrated with comments on their taxonomic status. Close reexamination on them revealed that all species are identical or closely related to Japanese ones, but none of Japanese species are affected by those names.

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