Crinoids are marine animals that make up the class Crinoidea of the echinoderms (phylum Echinodermata). The name comes from the Greek word krinon, "a lily", and eidos, "form". They live both in shallow water and in depths as great as 9,000 meters (30,000 ft). Those crinoids which, in their adult form, are attached to the sea bottom by a stalk are commonly called sea lilies. The unstalked forms are called feather stars or comatulids.