The hermit crab, Eupagurus, shares its welk shell with a ragworm, Neris, which lives inside and a sea anemone, Calllactis, which is attached to the outside of the welk shell. The ragworm gains protection and benefits from the scraps which break off the crabs food. The sea anemone also benefits from these scraps, as well as from the crabs mobility. The
crab gains protection from the sea anemones tentacles which are armed with stinging cells.