奄美大島と伊豆半島におけるカワニナの分布と成貝および新生貝の種内変異
2000 年 59 巻 2 号 p. 149-163
詳細
2000 年 59 巻 2 号 p. 149-163
The distribution of a freshwater snail, Semisulcospira libertina was surveyed at 26 localities including the type locality in Japan. Intraspecific variations in the shell feature of adult snails, the size of newborns and the number of births in a year were investigated. Surface of adult shells from Amami-Oshima (type locality) and Izu Peninsula was similarly smooth, but that at Lake Ashinoko, the lake type of S. libertina, had prominent ribs. Intraspecific variations of the size and the microsculpture of the newborns between Amami-Oshima and Izu Peninsula were found. Microsculpture on the newborn shells at 12 localities was classified into 3 types, smooth type in Amami-Oshima, keel type in Izu Peninsula and developed nodes type in Lake Ashinoko. The mean sizes of newborns at 12 localities were classified into 2 types, medium and small type. The mean size of the newborns in the medium type, i.e. 0.8 mm of shell diameter and 1.1-1.2 mm of shell height, showed only a little variation at Amami-Oshima and Izu Peninsula. The mean size in the small type collected at 2 localities in Izu Peninsula, were 0.6mm of shell diameter and 0.8 mm of shell height. Average numbers of newborns during one year in the medium type were estimated 400-531, which were less than that in the small type as previously reported in Tokai District.
