A new species of naticid snail is described from Okinawa Island, East China Sea : Naticarius pumilus n. sp. It is the smallest species found so far in the family Naticidae and has a multisulcate operculum, the outermost spiral rib of which is bevelled and has tile-shaped projections. This species is morphologically different from all of its congeners by shell size, shell color pattern and sculpture of operculum.

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Trophon eversoni n. sp. is described. The new species is morphologically close to T. geversianus (Pallas, 1774), T. scotianus Powell, 1951, T. plicatus (Lightfoot, 1786), T. longstaffi Smith, 1907, T. leptocharteres Oliver & Picken, 1984, and T. albolabratus Smith, 1875, but differs in having a larger shell, more numerous and regularly shaped spiral cords, and high, thin, abaperturally sloping axial lamellae.

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Experiments on the climbing behaviour and tolerance to aerial exposure of a freshwater mussel, Limnoperna fortunei (Dunker), were carried out in the laboratory with virtually constant temperature and humidity. Two hundred mussels with 4 to 34 mm in shell length were individually placed on the bottom of the cylindrical plastic vessels with water of 10 cm deep, and they were left in the dark during 23 hours. Fifty six mussels (28%) showed a negative geotaxis, climbing the vertical walls of the vessels and attaching above the bottom with their byssal threads. Mean height of the attachment sites from the bottom was 6.8 cm. Smaller mussels tended to exhibit this climbing behaviour with greater frequency than larger mussels. Mussels showing this climbing behaviour were then exposed to air of 26-30℃ and ca. 75% humidity for 10 days. Seven out of the 56 mussels returned to the bottom within 2 days after exposure, but all other mussels stayed above the bottom throughout the experiment and died within 10 days. Mussels not showing the climbing behaviour were individually put in empty glass Petri dishes and exposed to air of ca 28℃ and 75% humidity, and their survival was checked every day. All small mussels with 5-10 mm shell length died within 5 days after exposure, but mean survival days increased with increasing shell length. All mussels died within 10 days after aerial exposure. The adaptive significance of this climbing behaviour and difference in the tolerance to exposure to air between small and large mussels are discussed with a focus on the effective escape response against siltation, predation or brackish water in the field.

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Limnoperna fortunei fortunei (Dunker, 1856) and L. fortunei kikuchii Habe, 1981 were introduced in Japan in the 1990's and 1970's, respectively. The latter has been recognized as a subspecies on the basis of features of shell morphology. However, validity of its subspecific status has been questioned, because these two mytilids are clearly distinguished also by several other characteristics. In the present study, genetic differences were examined between these two mytilids, which were collected from two sites in the Nagara River flowing into Ise Bay along the Pacific coast of central Japan. The sample of L. fortunei fortunei was from an upstream site while that of L. fortunei kikuchii was from a downstream site. Examination of these samples for 10 enzymes using gel electrophoresis showed genetic variation to be found at 14 loci, 13 of which indicated complete allelic substitution between the two samples. No hybrid was observed in samples containing the two mytilids. Nei's genetic distance (D) was very high (2.78) between the two. The observed average heterozygosity (Ho) was 0.0048 in L. fortunei fortunei and 0.0783 in L. fortunei kikuchii, the values being significantly different between the samples. These support that their genetic difference would be in the specific level.

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Bradybaena pellucida exhibits shell color and banding polymorphism. We have found four shell types : yellow-unbanded (YU), yellow-banded (YS), brown-unbanded (BU), and brown-banded (BS), in Tateyama, Chiba. Asami et al. (1993) has shown the genetic dominance of the banded morph to the unbanded. In the present study, we tested the mode of inheritance of the shell color by crossing experiments. The results indicate that the brown allele (C^B) is dominant to the yellow allele (C^y). In a testcross of BS and YU, offspring segregated in two phenotypes, YS and BU. This suggests that loci for shell color and banding are tightly linked and the BS parent was a double-heterozygote with domonant alleles at the trans-position.

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There are two species belonging to the genus Unio in Japan. They resemble each other in the shell morphology, but color of glochidia is different : buff in Unio douglasiae nipponensis and milky white in U. biwae. In the present study, species identification was carried out based on this character. Although the pseudocardinal tooth on the right valve was thicker in U. biwae than in U. douglasiae nipponensis on the average, the ranges of variation were overlapped largely. Moreover, experiments proved that hybridization between them occurred easily when they reared together. U. biwae was only found in and around Lake Biwa, while U. douglasiae nipponensis was never found there, though it was distributed in the lower reaches of the water system of Lake Biwa. As there was no distinct difference in the shell morphology and no overlap of distribution between them, it may be better to regard U. biwae as another subspecies of U. douglasiae. This subspecies U. douglasiae biwae is endemic in Omi Basin.

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The cephalopods removed from 16 stomachs of Gasterochisma melampus collected in the eastern South Pacific were examined. Sixteen species of 12 families were identified from the materials, the most of which were mesopelagic species. A chiroteuthid squid Planktoteuthis oligobessa was newly recorded from the South Pacific. Almost of all species were common to the California Current fauna.

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[in Japanese]

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