Maturation, spawning and development in Siphonaria Pectinata linnaeus (Gastropoda: Pulmonata) at Gibraltar

摘要

A comparative study of some aspects of the reproductive biology of Siphonaria pectinata was carried out at Gibraltar. Maturation occurred at 5-6 mm shell length corresponding to an age of 6-12 months. At the more sheltered Atlantic site spawning was evident from March to June 1992 with peak spawning occurring in May-June 1992. The patterns of spawning activity for the following two years were very similar. Egg ribbons were very scarce at the more exposed Mediterranean site and were found in considerably less quantities than at the Atlantic site. Individuals at both sites contained mature eggs in their gonads at the onset, and then throughout the duration of the spawning season, but exhibited spent gonads by October. The spawn of S. pectinata consisted of small oval ribbons filled with numerous egg-shaped capsules spaced irregularly in a jelly-like matrix. Spawn was deposited mainly away from the home scar in shallow depressions, cracks and crevices and between barnacles and mussels. S. pectinata exhibited planktonic development. The fertilised eggs took between 14 and 21 days to develop at ambient temperature (14-19 deg C). and hatched as free-swimming planktotrophic veligers. The timing of spawning activity and the placement of egg masses in protective microhabitats on the shore are discussed in terms of adaptations to reduce desiccation stress, predation and possible food shortages. The mode of development in S. pectinata is placed in context with current theories regarding siphonariid ancestry and evolution.