マルタニシの生活状態

概要

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The present paper is dealt with the life of Viviparus malleatus found in Niwa-gun of the northwestern part of Aichi Prefecture. The relation between the diameter of opercle and the body weight indicates the primary function. In larger specimen, the female is heavier than the male. The specimens with the opercle measuring less than 20mm in diameter are very common. The sex ratio indicates that the female is more numerous than the male among larger specimens, and the male is more abundant among smaller specimens. In general, however, specimens with opercle less than 25mm in diameter are predominantly males. The maximum life year is four years in the male and seven years in the females. In the natural state one to two year old specimens are commonly found in the field and four year ones are distinctly few. The young are born from April to August and found throughout year. The growth of young 20 days after hatching is rather rapid and then gradually becomes slow. When the water temperature is lower than 15°C, the growth may cease. The growth rate during the second year is slower than the first and still so in the third year.