shed

Many other animals "shed" their skin, not only snakes...as in the last post.... Crabs (and other crustaceans) cannot grow in a linear fashion like most animals. Because they have a hard outer shell (the exoskeleton) that does not grow, they must shed their shells, a process called moulting. Just as we outgrow our clothing, crabs outgrow their shells.

Here a Sally lightfoot crab in the Galápagos is bubbling prior to shedding its skin

and here is a full moult of a hermit crab in Hong Kong (its body in the shell does not have a hard outter skeleton as its in the shell!)