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

Abstract

Patterns of gametogenic activity in three prosobranchs with internal fertilization, Bumupena 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 pnor to copulation could not be ruled out it is suggested that the time spans identified be regarded as 'potential' rather than 'effective' breeding periods. Patrone van gametogeniese aktiwiteit in drie prosobranche, Burnupena lagenaria, Nerita albicilla, en N. plicata, wat interne bevrugters is, is bepaal. Geen seisoenale patrone is gevind in die histologiese voorkoms van die gonades van N. albicilla en dit blyk dat gametogenese 'n aaneenlopende proses is. Vier duidelike reproduktiewe fases, onaktiwiteit, gametogeniese opbou, aktiewe dooiervorming of spermiogenese, en 'n post-kuitskiet-fase was egter waarneembaar in B. lagenaria en N. plicata. Alhoewel volwasse gamete reg deur die jaar gevind is in die gonades van N. plicata, het post-kuitskiet-indiwidue oorheersend tussen Maart en September voorgekom, wat daarop dui dat die broeiperiode wei korter mag wees. Gametogeniese ontwikkeling is swak gesinkroniseer in B. lagenaria maar 'n verhoging in reproduktiewe aktiwiteit was wei waarneembaar tussen April en November. Eieromhulsels is gedurende hierdie periode in die natuurlike omgewing gevind. Die eieromhulsels en hul inhoud word ook beskryf. Aangesien opeenhoping en storing van gamete voor kopulasie kan plaasvind, word voorgestel dat die ge'identifiseerde broeiperiodes beskou word as 'potensiele' eerder as 'effektiewe' broeiperiodes.