ナカセコカワニナとハベカワニナの産仔数と新生貝の大きさ

概要

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The number and size of newborns in Semisulcospira nakasekoae and S. habei were studied under the laboratory conditions. The number of newborns released by each mother was recorded daily under the laboratory conditions where mother snails were reared individually during 15 months. Average number of newborns released during one year in S. nakasekoae and S. habei was estimated at 26-53 (max. 83) and 74-145 (max. 161), respectively. Birth of newborns in these two species occurred at a water temperature between 12℃ and 24℃. Mean size (shell diameter) of newborns in S. nakasekoae and S. habei was estimated at 1.6-2.2 mm (max. 3.0 mm) and 1.4-1.5 mm (max. 2.5 mm), respectively. Maximum shell height of newborns in these two species was 3.6 mm and 2.9 mm. Mean number of whorls of newborns in these two species was 2.8-3.5 and 2.9-3.0. The large size of females in S. nakasekoae showed a tendency to produce the large size of newborns. But, the large size of females in S. habei showed a tendency to produce the large number of newborns. The number and size of newborns in the two species were discussed in relation to the number of shelled embryos and the size of adult females.
1994-10-31