Maturation, Spawning and Development in Siphonaria Pectinata Linnaeus (Gastropoda: Pulmonata) at Gibraltar |
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Authors: | Ocana Terence M J; Emson Roland H |
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Institution: |
* Mediterranean Institute of Ecology, 49 Northview Terrace, Devil\rquote s
Tower Road, Gibraltar.;
Division of Life Sciences, King's College London, Campden Hill
Road, London W8 7AH, UK |
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Abstract: | A comparative study of some aspects of the reproductive biologyof Siphonaria pectinata was carried out at Gibraltar. Maturationoccurred at 5-6 mm shell length corresponding to
an age of 6-12months. At the more sheltered Atlantic site spawning was evidentfrom March to
June 1992 with peak spawning occurring in May-June1992. The patterns of spawning activity
for the following twoyears were very similar. Egg ribbons were very scarce at themore exposed
Mediterranean site and were found in considerablyless quantities than at the Atlantic site.
Individuals at bothsites contained mature eggs in their gonads at the onset, andthen throughout
the duration of the spawning season, but exhibitedspent gonads by October. The spawn of S.
pectinata consistedof small oval ribbons filled with numerous egg-shaped capsulesspaced
irregularly in a jelly-like matrix. Spawn was depositedmainly away from the home scar in
shallow depressions, cracksand crevices and between barnacles and mussels. S.
pectinataexhibited planktonic development. The fertilised eggs took between14 and 21
days to develop at ambient temperature (14-19°),and hatched as free-swimming
planktotrophic veligers. The timingof spawning activity and the placement of egg masses in
protectivemicrohabitats on the shore are discussed in terms of adaptationsto reduce desiccation
stress, predation and possible food shortages.The mode of development in S. pectinata is placed in contextwith current theories regarding siphonariid ancestry and evolution. (Received 6 January 1998; accepted 25 June 1998) |
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