カワニナの生態学的研究

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The fresh water snail, Semisulcospira libertina was investigated ecologically at 3 stations with different ecological conditions in Sagamihara, Kanagawa Prefecture, from May 1967 to April 1968. Two hundred snails were randomly collected monthly by means of a 1 mm mesh sieve at each station. The snails collected were separated into groups according to the length of the penultimate whorl because the apex was usually eroded in older shells. Most of the juvenile snails under 1 mm in the length was delivered twice a year from May to July and from October to November. The juveniles appeared in greater number in autumn than in spring at stations 1 and 2 where water temperature was high in summer and low in winter, whereas their number was greater in spring in station 3 which was supplied with water by a spring and had no great thermal fluctuations through the year. Mature snails were generally above 3 mm in the length and those under 3 mm could not be differentiated sexually. The female snails with embryo shells in the brood pouch were observed abundantly in summer and winter, whereas they decreased abruptly in number in spring (April and May) and autumn (September and October), when the brood pouch contained only a small number of embryos and achieved a vesicular appearance. The snails grow very rapidly ; as observed in station 1, juvenile snails were 1 to 1.5 mm in shell length just after delivery and 20 to 25 mm one year after it ; and growth rate was greatest in station 2 where the water contained much organic matters, while it was smallest in station 3 which was supplied with water containing much less organic matters by a spring. Consequently, organic matters in the water seemed to have a great influence on shell growth. It will take about one year for female snails to become mature and pass offsprings, and the life span of the snail appeared to be 1 to 1.5 years, 2 years at the longest. The sex ratio of S. libertina was 1 : 1 in the stations examined.
日本貝類学会の論文
1978-07-31

カワニナの生態学的研究

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