||Cys*tid"e*a (s?s-t?d"?-?), n. pl. [NL., fr. Gr. &?;&?;&?;&?; a bladder, pouch.] (Zoöl.) 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.