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You are here:   animal list > Cypraea annulus




Cypraea annulus Linnaeus, 1758

Gold Ring Cowry

Lauren Hughes (2011)


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Growth & Development

In all gastropods, development is spiral and all members undergo torsion after larval formation. Torsion is a 180 degree counter-clockwise rotation of the visceral mass, shell, mantle and mantle cavity with respect to the head and foot. This developmental process establishes the larval body plan. The cowry, like most gastropods, has a shell that consists of multiple coils which form a spiral around a central node. This coiling is more obvious in juveniles compared with adults in which coils can be seen inside.

Juvenile cowries have a typical gastropod shape with an exsposed spire, large aperture and thin outer lip. Growth occurs as the juvenile cowry extends its shell by increasing the length of the last coil. At maturation, the aperture shrinks to a small slit. At the same time, the shell becomes thicker and decorated and the shell does not obviously show coiling. The folding in of the outer lip also shrinks the aperture. As an adult, coil lengthening apparently stops and growth is limited to shell thickening and decoration (Katoh 1989). The gold ring cowry has been found to enhance it's fitness by growing rapidly as a juvenile to achieve a bigger size but with fragile and thin shells. Many other gastropods utilise an alternative strategy in which juveniles grow slowly to create a strong and thick shell. Once the gold ring cowry reaches size at adulthood, the begin to thicken their shell. However, callus thickness has been found to increase at lower latitudes (Irie & Iwasa 2003). This variation in shell morphology with latitude is thought to be related to a latitudinal gradient of shell-crushing predation pressure or an environmental factor promoting shell thickening, e.g. sea water temperature.