The Collaborative International Dictionary of English v.0.48:

Clypeastroid \Clyp`e*as"troid\, a. [NL. Clypeaster (L. clupeus
   shield + aster star) + -oid.] (Zool.)
   Like or related to the genus Clupeaster; -- applied to a
   group of flattened sea urchins, with a rosette of pores on
   the upper side.
   [1913 Webster]