ˌekəˈnȯidēə noun plural
Usage: capitalized
Etymology: New Latin, from echin- + -oidea
: a class of motile bottom-dwelling echinoderms comprising the sea urchins and related forms having a disk-shaped shell formed of regular and usually united plates studded with tubercles bearing spines and with pedicellariae and pores through which the tube feet emerge and most having a characteristic complicated system of pentamerous jaws in the mouth — compare aristotle's lantern , centrechinoida , cidaroida , exocycloida