The Reproduction, Growth and Distribution of Calyptraea chinensis (L.)

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Abstract
Samples of this protandrous mollusk were collected from the Yealm Estuary, Plymouth. The sexual phases are defined. Males, immature and functional females were separated by analysis with probability paper and by examination of the yearly growth rings. The methods were compared and analysis with probability paper was shown to be satisfactory. Sexual association was greatest from October to March, during which time there was no growth. Growth rates are shown for each age group. The mean diameters of associating males and females are shown. Spawning occurred from May to October and commenced when the sea temperature reached 10[degree]C. Embryos were found until October. Functional females spawned twice in the summer and laid an average of 250 embryos in the second spawning. Further spawning was precipitated by removal of spawn. Periodic spawning at the new moon occurred in 1952, 1953 and 1954 and at other times in 1954. At the end of the breeding period, many functional females died before the temperature fell. In their first year all animals were males. All became females during their second year and spawned when 2 years old. Association of the newly functional females began suddenly at the end of September. The distribution is reviewed. Animals introduced on oysters breed in a Scottish Loch, but have not survived in Essex. Distribution is not limited by summer temperatures affecting spawning directly. At Plymouth, the few associations in the winter of 1954-1955 and the higher percentage (70%) of unfertilised eggs in 1955 are linked with reduced shell growth in the summer of 1954, to unusually low sea temperatures in July and August, 1954.

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