Shell opening by crabs of the genus Calappa.

Oxystomatous crabs of the subfamily Calappinae, particularly the genus Calappa, possess a large tooth on the dactyl and a pair of protuberances on the propodus of the right cheliped. With these modifications and an associated behavior pattern, these crabs can efficiently open shells of gastropods and other mollusks and thus feed on the soft parts or enclosed hermit crabs.