Shelter preferences in the endemic Bermudian hermit crab, Calcinus verrilli (Rathbun, 1901) (Decapoda, Anomura)

Calcinus verrilli, a hermit crab endemic to Bermuda, is unusual in that it inhabits both gastropod tubes (Vermicularia spp. and Dendropoma spp.) and gastropod shells (Cerithium litteratum). It was found in both shelter types, in Five marine environments, categorized as intertidal areas, subtidal areas, boilers, patch reefs, and rim reefs. We found most males in shells and most females inhabiting tubes. We discovered a size dimorphism, females being larger than males. In the laboratory, when given a choice between shells and tubes, both males and females showed a significant preference for shells. In a Y-maze test of attraction to extracts from tube-forming versus shell-forming gastropods, males showed no discrimination, but females preferred the tube-associated extract. These shelter and size dimorphisms in C. verrilli are best explained by intrasexual competition and differences in the ecology of males and females.