While the beaked crab has one backbone and one mouth, most of the other cave dwellers have two. Two-headed centipedes pick shells clean, as do the hand crabs. Sometimes resembling hands, hand crabs have anywhere from five to thirteen legs, with the odd one being directly in front between the two mouths. It uses this appendage to break up and wedge apart shells. Hand crabs also have an outer protective shell to retract into, the extensions around their legs resembling sleeves.
Pyramid crabs have much thicker shells with an angled design that makes it hard to get a grip on them. Their forward appendage (which fits in a notch on this shell when raised) is very strong and ends in a massive claw. It uses this not only to smash open shells, but for defense and to right themselves should they be flipped over.