Reproductive biology of two species of Turbinidae (Mollusca : Gastropoda)

Abstract

Turbo intercostalis Menke, 1843 and Turbo torquatus Gmelin, 1791 were found to be dioecous with 1:1 sex ratios. In both species, the testis was creamy-white and the ovary green, although infection of the gonad of T. intercostalis by trematodes resulted in abnormal gonad colours. The right kidney opening of both female and male T. intercostalis was developed into a sexually dimorphic papilla. while the tissues around the genital opening of both sexes of T. torquatus were only formed into small lips. The histology and histochemistry of the papillae and lips were examined with regard to the possible mode of spawning in these species. The evidence indicated that both species spawned their eggs to the plankton. Reproductive cycles were investigated by histological examination of regular gonad samples and the number of mature and immature oocytes in a subsample of the ovary determined. The testes were not examined quantitatively but the presence of fully spawned males in the samples was noted. Gametogenesis was continuous in both species. T. torquatus showed several spawnings per year. with a peak of activity in summer. Spawning of T. intercostalis occurred from autumn to spring, although in one year a summer spawning occurred. Examination of populations of T. intercostalis near the extremes of the species' range suggested that reproductive difficulties may contribute to limiting the distribution of the species at the southern (low temperature) end of its range.