Hermit crabs and sea anemones share an unusual and intimate underwater relationship. Young hermit crabs will often pick up a young sea anemone to attach to their shell and they become partners for life.
They even grow at roughly the same rate. When hermit crabs outgrow their shell, they often take the sea anemone with them to the new one.
Some sea anemones have gone so far as to cover most of the surface of the hermit crab’s shell so when the crab eventually outgrows the shell, he doesn’t have to move.
The relationship of the hermit crab and sea anemone serves both a multitude of purposes.