Two chromodorid species, Glossodoris pallida (Ruppell & Leuckart, 1828) and Hypselodoris purpureomaculosa n. sp., are described. The specimens of both species were collected separately from the eastern coast of Middle Japan.

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Although most of the larger Turbo species were described in the 18th and 19th centuries, the authors describe a new species from West Irian, formerly Dutch New Guinea. The species is compared to related congeners, most of them living sympartrically.

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Anatomical features of "Trochochlamys" praealta (Pilsbry, 1902) was examined and the soft part morphology is described. "T." praealta is characterized by having simple male genitalia lacking any accessory organ, minute radulae, slender central teeth, reduction of lateral teeth and numerous marginal teeth with serrated ectocones. Although the present species has been placed in the genus Trochochlamys, the observed anatomical features, especially the unique radular features, agree with those of the genus Coneuplecta. Taxonomic position of the present species is therefore transferred from the Trochochlamys to the genus Coneuplecta. C. praealta collected from Mt. Izuru, Tochigi Pref. exhibits unusual genitalia with deficient male genital organs, which is called a hemiphallic sexual morph. These hemiphallic snails exhibit reduction not only in the male organs but also in some presumed female organs, such as bursa copulatrix and carrefour gland. Although the hemiphallic sexual morph has not been recorded in the subfamily Euconulinae of the family Helicarionidae, previous descriptions of euconuline genitalia suggest that hemiphally is not rare in these taxa. Taxonomic significance of the hemiphallic sexual morph in euconuline helicarionids is discussed. Possible convergent evolution of the Coneuplecta-type radulae is also discussed.

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Growth and number of newborns in Semisulcospira kurodai reared during 48-52 months under the laboratory conditions were studied. The newborns, which were produced in July 1988 and August 1989, grew up to 10.3mm in mean shell diameter by the age of 1, 11.0mm by the age of 2, 11.5-11.8mm by the age of 3, and 12.0mm by the age of 4. The maximum size of S. kurodai is 13.3mm in shell diameter, 52.0mm in shell height, 7.7g in wet weight with shell at the age of 4. The production of newborns has begun in snails grown up over 9mm in mean shell diameter at the 8-10th months after the birth. Birth of newborns occurred at a water temperature between 12℃ and 24℃. Large number of newborns were produced at a water temperature over 20℃. Number of newborns produced during a month per female is estimated 10-20 individuals at water temperature between 20℃ and 24℃. Large number of newborns during a year were produced by mature females larger than 10mm in mean shell diameter at 1-3 ages. Mean number of newborns produced during a year per female at 1-3 ages is estimated 62-79 individuals.

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The behaviour of the outer epithelial cells of a mantle allograft implanted into the mantle connective tissue of the mussel Hyriopsis schlegeli was examined using light and transmission electron microscope. Ultrastructural observations revealed that the outer epithelial cells of an implanted allograft separated from their original basement membrane, emerged from the periphery of graft, very soon flattened and emigrated crawling in contact with the plasma membrane of agranular hemocytes in the recipient hemocyte capsule surrounding the graft. In this behaviour the emigrating outer epithelial cells spread out as a monolayer of continuous cell sheet of flattened cells which connected each other by desmosome. It seems that the marginal cells situated in the growth front of the continuous epithelial cell sheet stretch some filopodia from their leading edge, emigrate recognizing the plasma membrane of recipient agranular hemocytes by contact and regenerate into a monolayer of pearl-sac epithelium which aligns on the inside of hemocyte capsule.

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Two Miocene species, Thracia kamayasikiensis Hatai and T. higasinodonoensis Oinomikado were found as the relict species from the Pliocene Ogikubo Formation in Nagano Prefecture, Central Japan. From this formation, Thracia kakumana (Yokoyama) which is a common species in the Pliocene to Recent boreal faunas was also occurred. In spite of the extinction of the most Miocene thraciids by the latest Miocene cooling, the above two species survived in the studied area by the Middle Pliocene, owing to the cold embayment conditions.

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Nucleotide sequences of mitochondrial genes of Calyptogena laubieri, that had been thought to be a synonym of sympatric congeneric species, C. kaikoi, were compared with those of C. kaikoi and another sympatric congeneric species, C. nautilei. Large differences among their sequences showed that C. laubieri should be treated as a valid species. The phylogenetic analysis of the Calyptogena species collected around Japan suggests that the subgenus Ectenagena is not a monophyletic group.

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Sinking rates of the intact eggs and the hull-removed eggs of Acanthopleura japonica were measured. The mean sinking rate of eggs with hulls was 0.275mm/s, while that without hulls was 0.794mm/s. Results indicate that hulls reduce the sinking rate of eggs, thus suspending them longer in seawater, presumably for increasing the chances of successful fertilization.

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