When darkness falls, these small bodied long armed ophiuroids slip out from beneath the rocks or sea weed, and propel themselves forward, twisting and writhing like small octopuses. A piece of fish dropped in the aquarium sends them into a frenzy of lashing arms, as they wrap themselves around the food, writhing and heaving until its devoured. Guaranteed to catch the attention of even the most bored, uninterested student.