Crinoids are marine animals that make up the class Crinoidea of the echinoderms. The name comes from the Greek word krinon, "a lily", and eidos, "form". They live in both shallow water and in depths as great as 9,000 meters. 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.