The Collaborative International Dictionary of English v.0.48:

Cystidea \Cys*tid"e*a\ (s?s-t?d"?-?), n. pl. [NL., fr. Gr. ????
   a bladder, pouch.] (Zool.)
   An order of Crinoidea, mostly fossils of the Paleozoic rocks.
   They were usually roundish or egg-shaped, and often
   unsymmetrical; some were sessile, others had short stems.
   [1913 Webster]