Hermit crabs live in empty shells to protect their tender backsides. A hermit crab may change its shell when it finds a more attractive or better-fitting one. Some hermit crabs put anemones on their shells. One small Xanthid crab carries sea anemones around in its claws. When frightened, it waves the anemones like boxing gloves to ward off predators.
Sponge crabs carry sponges to camouflage themselves.
The sponge is held above the body by the crab's rear pair of legs. The small Decorator crabs have many hooks on their bodies which they use to attach pieces of algae, sponges, and hydroids. This practice makes them very hard to spot among algae-covered rocks or reef flats. Several fish change their appearance as part of their life-cycle or as a defense. When alarmed, they distend themselves with water into round, prickly balloons, making themselves larger and more difficult to eat.