GEOGRAPHICAL VARIATION OF SHELL MORPHOLOGY IN CYPRAEA ANNULUS (GASTROPODA: CYPRAEIDAE)

Macro- and microgeographic variation of shell morphology inCypraea annulus was studied. Surveys of phenotypic variationin 19 populations from the Indian and West Pacific Oceans revealeda significant positive relationship between average seawatertemperature and callus thickness. In contrast, juvenile shellsize after maturation had no significant relationship with seawatertemperature. Research on within-population variation in OkinawaIsland indicated that shell morphology is correlated with someecological factors such as temperature and algal abundance.Both juvenile shell size and callus thickness decreased withincreasing density of individuals. These microgeographical patternssuggest that ecophenotypic variation, rather than genetic differentiation,causes the latitudinal clines in shell morphology that havebeen reported in several cypraeid species. (Received 18 November 2004; accepted 8 April 2005)