Gymnodoris striata of Baba, 1937 is re-identified as Analogium amakusanum n. sp. It is re-described.

View full abstract

One new species of bivalve, Felaniella (Zemysia) ohtai Kase and Miyauchi, of the family Ungulinidae is described. This new species is common in shallow waters off the western coast of Wakkanai, Hokkaido and the first species of the subgenus Zemysia from the northwestern Pacific. The fossil forms of this species are known from the lower Pleistocene of Sado and the upper Pliocene of Akita, suggesting that this species provided into Japanese waters in late Pliocene age and extended its distribution more south than the living specimens.

View full abstract

Seasonal and vertical variations of size structure and recruitment of Monodonta labio (Gastropoda : Trochidae) were investigated by periodical quantitative sampling on a boulder shore in Amakusa, west Kyushu, Japan. Size frequency histograms are constructed using bimonthly data from October 1987 to October 1988 at 11 tide levels (TL). The size structure of M. labio differed between tide levels and fluctuated seasonally. Generally, juveniles (<5 mm in shell width) occurred in the mid zone (TL5-7) throughout the year. Small snails (5-9 mm) and middle sized snails (9-13 mm) occurred in the high zone (TL1-4) and large snails (&ge;13 mm) appeared mainly in the low zone (TL8-11). So the size structures in the high and the low zones tended to show unimodal distribution, the mode being around 10 mm and 12-14 mm, respectively. Bimodal distributions were generally observed in the mid zone, the modes corresponding to juveniles and large snails. Recruitment of juveniles was observed mainly in the mid zone from October to June. However, the average level distribution of juveniles fluctuated seasonally. Factors affecting the recruitment and size structure were discussed.

View full abstract

Two colour morphs of Facelinella quadrilineata spawned slightly different egg masses and the eggs enclosed were also different in colour and size. The time required for embryonic development of larger ova was always longer than that of smaller ones. Both of them hatched as lecithotrophic veliger larvae with relatively small vela, welldeveloped large eyespots and propodium, although the shell shape and size were fundamentally different between the two morphs. These findings, together with sympatric and simultaneous occurrence, strongly suggest that the two colour morphs represent two distinct species.

View full abstract

The distribution of the arboreal snail Euhadra amaliae was studied in relation to tree species and position on the tree in a small woodland garden. The snail occurred, from spring to autumn, more abundantly on some deciduous trees such as Cudrania tricuspidata and Poncirus trifoliata. The height above ground of the snail position was higher in the summer. The proportion of snails on branches was lower in the summer when foliage was thickest. The snails also occurred on branches in higher proportion on days when activity was greater. Most of the snails on leaves were recorded from the under side. Thus, the snails had some preference for tree species and position on the tree, with some daily and seasonal differences.

View full abstract

[in Japanese]

View full abstract