Crustaceans, Pacific Northwest
The hermit crab is a land or water-dwelling crustacean. Unlike true crabs, hermit crabs have soft, vulnerable abdomens. For protection from predators, many hermit crabs seek out abandoned shells, usually snail shells to live in. A hermit crab’s soft body is naturally flexible and can twist easily to fit into the spiral interior of a snail’s shell. When a hermit crab finds one of the proper size, it pulls itself inside, leaving several legs and its head outside the shell. A hermit crab carries the shell wherever it goes. When it outgrows its shell, it finds a larger one to move into. Sometimes, hermit crabs carry other sea creatures on its shell, such as sea anemones. These creatures help camouflage the crabs.
Most adult hermit crabs are from 13 mm to 121 mm long. They live on the seashore in tide pools or on the ocean bottom in deeper water, hermit crabs scavenge their food.
The hermit crab has two pairs of antennae and round eyes on the ends of eye stalks. Hermit crabs have 10 legs, but only 6 legs show. These front 6 legs are known as walking legs. Hermit crabs keep their 4 back legs inside their shell. The back legs are much smaller than the walking legs.
The front pair of legs end in claws or pincers. The left front leg has a large pincer, which the crab uses for moving around and defending itself. When the animal is hiding inside its shell, it uses this pincer to seal off the shell’s opening. The right front leg has a smaller pincer, which the crab uses to eat and drink. Both front pincers have thick layers of an exoskeleton.
If you look into just about any tidal pool at low tide, you will see these little ones crawling about. They are quite beautiful when they are peeking out from their shells.