A sea anemone and hermit crab share a snail shell, providing a wonderful example of commensalism. The anemone (like all cnidarians) has stinging cells that help protect the crab from predators and benefits from having a free ride around the seafloor habitat, as well as receiving scraps from the crab's feeding activities. When the crab outgrows its borrowed shell, it finds a larger vacant shell...and brings the anemone along to share its new home.