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Webster 1913 Edition
Echinoidea
‖
Echˊi-noi′de-a
,Noun.
pl.
(Zoöl.)
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
.]