Relation of growth rings to reproductive cycle in Cryptopecten vesiculosus, a dimorphic pectinid bivalve

Abstract

The relation between growth rings and reproductive cycle in a dimorphic pectinid bivalve, Cryptopecten vesiculosus (Dunker, 1877) was examined histologically on the basis of semi-regularly collected samples from Sagami Bay. This pectinid is hermaphroditic. Male and female gonads ripen between June and September, and spawning occurs during July to November. A strong growth ring is formed just before spawning, and the first ring indicates that the specimens has reached the stage of sexual maturity. This means that growth rings are formed once a year after the individual reaches sexual maturity. No visual difference was detected in the gonad development between the two phenotypes; their gonadal weight indices are statistically identical throughout the year. Therefore the previous interpretation that the dimorphism represents discontinous intrapopulational variation is upheld. The results of this study are applicable to life history analysis in extant and fossil populations.