Ornament on Hermit crab shell

The hermit crab is an anomuran decapod crustacean of the superfamily Paguroidea. There are more than 800 species, most of which have an asymmetrical abdomen protected by a shell.
Hermit crabs' soft abdominal exoskeleton means they must occupy shelters produced by other organisms or risk becoming helpless. Adapted to occupy empty mollusk shells