Gametogenic activity in three internally fertilized prosobranchs from southern Africa, with notes on the egg capsules of Burnupena lagenaria

Abstract

Patterns of gametogenic activity in three prosobranchs with internal fertilization, Burnupena lagenaria, Nerita albicilla, and N. plicata, were determined. No seasonal trends were evident in the histological appearance of N. albicilla gonads, indicating that gametogenesis was a continuous process. Four distinct reproductive phases, inactivity, gametogenic build up, active vitellogenesis or spermiogenesis, and postspawning were recognizable in B. lagenaria and N. plicata. Although mature gametes could be found throughout the year in the gonads of N. plicata the prevalence of post-spawned individuals between March and September suggested that the breeding period may be less protracted. Gametogenic development in B. lagenaria was found to be poorly synchronized, although an intensification in reproductive activity was evident between April and November. Egg cases were also found in the field during this period. A brief description of these cases plus their contents is presented. Since gamete accumulation and storage prior to copulation could not be ruled out it is suggested that the time spans identified be regarded as ‘potential’ rather than ‘effective’ breeding periods.