Hermit crabs live in shells made and then abandoned by snails

Hermit crabs live in the empty shells of snails. When they hatch from eggs, the crabs are tiny and swim in the open water, along with many other creatures called "plankton". Those which survive will molt their real shells, grow in size and settle to the bottom of the ocean. Lobsters do the same thing. Unlike lobsters however, the young hermit crabs have very soft tails. They use them to squeeze into abandoned snail shells. The crab then only leaves its shell to molt its own shell in order to grow bigger. Often the bigger crab has to then find a larger snail shell. Some species of hermit crabs gain added protection by adopting sea anemones. They place the anemone on the back of their shell. The crabs are messy feeders and the anemone enjoys the scraps. The anemone has many stinging tentacles and this helps protect the crab from anything with jaws strong enough to crush a snail's shell. If the hermit crab needs a larger shell, it gently prods the anemone off the old shell and places it on the new one. Hermit crabs are related to giant Alaskan king crabs and coconut crabs. Only hermits use abandoned snail shells for protection, though.