Definition of Asteroidea
: the class of echinoderms comprising the starfishes, all being unattached, having (1) a star-shaped or pentagonal body, the rays or arms (usually 5 in number) hollow and containing prolongations of the coelom and alimentary and other viscera, (2) a skeleton of calcareous plates and ossicles somewhat loosely united, often allowing the arms great freedom of movement, and (3) a mouth on the lower surface without jaws or teeth, an aboral madreporic plate, and the anus often wanting or functionless (undigested matter being thrown out at the mouth), and moving by means of the arms or of long spines on the sides of the arms or by rows of tube feet that occur in a furrow on the lower surface of each arm
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