[1] : The Collaborative International Dictionary of English v.0.48

echinoidea \ech`inoi"dea\, n. pl. nl. see echinus, and
   -oid. zo"ol.
   the class echinodermata which includes the sea urchins. they
   have a calcareous shell, usually more or less spheroidal or
   disk-shaped, composed of many united plates, and covered with
   movable spines. see spatangoid, clypeastroid. written
   also echinidea, and echinoida.
   1913 webster
see also:
echinus -oid spatangoid clypeastroid echinidea echinoida 

[2] : WordNet (r) 2.0

echinoidea
     n : sea urchins and sand dollars syn: class echinoidea
see also:
class echinoidea 

Echinoidea >> E Words
Echinoidea, definition of term: Echinoidea
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