Some of the most important and interesting adaptations the hermit crab have developed is its diligent exploration and occupation of gastropod shells. Unlike other crustaceans, the hermit crab does not have its own shell. Instead, it needs to find a shell to occupy to protect itself from aquatic and terrestrial predators that exist in an intertidal environment.
The hermit crab is painstakingly careful in choosing a shell. It inspects and tests a number of shells before it is satisfied with one. Sometimes, hermit crabs fight with each other to get the shell they want. The discarded shell not only becomes a hermit crab's home, but it also protects its soft and exposed abdomen, which lacks a protective exoskeleton. Baby hermit crabs learn to seek out the shells of sea snails. To carry a load heavier than they are, hermit crabs develop strong hind legs, which clasp onto the sides of the shells as they crawl. If there are no shells to be found in its habitat, a hermit crab may settle for anything in which they can crawl and hide, such as a plastic cup or a broken liquor bottle.
Hermit crabs have long adapted to living on land. Although they have gills to breathe, these dry up, and they are eventually unable to breathe in oxygen through their gills. Hermits crabs, being terrestrial crustaceans, can drown when they are exposed to too much water or become dehydrated in the absence of water.