Hermit crabsPaguroidea

Hermit crabs are decapod crustaceans characterized by their soft, uncalcified abdomens, which they protect by inhabiting scavenged mollusc shells. The group's common name stems from this solitary, borrowed-home lifestyle. Their exposed bodies typically feature two pairs of walking legs, prominent antennae, and chelipeds (claws), often with one noticeably larger than the other. This larger claw serves both for defence and for sealing the shell entrance. Body length ranges from less than 1 cm (0.4 in) to over 10 cm (4 in) for visible species.

They occupy a variety of marine habitats including coral reefs, rubble fields, sandy bottoms, and seagrass beds, occurring from the intertidal zone down to depths exceeding 50 metres (165 ft). Hermit crabs feed primarily as scavengers and detritivores, consuming algae, small invertebrates, and organic debris. As they grow, they regularly exchange shells, seeking larger accommodations. Divers frequently encounter these crabs during both day and night dives.