The Collaborative International Dictionary of English v.0.48:

Asterioidea \As*te`ri*oid"e*a\, Asteridea \As`ter*id"e*a\, n.
   pl. [NL., fr. Gr. 'asteri`as + -oid. See Asterias.] (Zool.)
   A class of Echinodermata including the true starfishes. The
   rays vary in number and always have ambulacral grooves below.
   The body is star-shaped or pentagonal.
   [1913 Webster]