Predation and the geography of opercular thickness in turbinid gastropods

Abstract

The heavily calcified opercula of turban snails (Turbinidae) function as passive-defensive structures against predators that break the shell at the outer lip or that enter the shell by way of the aperture. Passive armour generally is more common and much better developed in the tropics than in colder regions. In line with this expectation, the relative opercular thickness of tropical turbinids (mean 0.358 ± 0.045, 33 species) significantly exceeds that of temperate species (mean 0.300 ± 0.051, 21 species). Small differences in relative opercular thickness occur among tropical biogeographic regions, but none is significant. Patterns observed among turbinids as a whole also appear in individual clades, indicating that the patterns are not dictated by a phylogenetic signal. © The Author 2007. Published by Oxford University Press on behalf of The Malacological Society of London, all rights reserved.