Fell, Howard B. Formerly, Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts.
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An extinct subclass of stalked or creeping Crinoidea which includes some 50 Paleozoic genera, ranging from Ordovician to Permian times. A flexible tegmen was present with open ambulacral grooves. One of the five oral plates served as a madreporite. The anus was at the tip of a short siphon. About three of the lower brachial ossicles of each arm were loosely incorporated into the dicyclic calyx. The three infrabasals were sometimes obscured by the stem, but the five basals and five radials remained conspicuous and movably articulated. The uniserial arms lacked pinnules but branched freely, arching inward to form a globular crown (see illustration). The cylindrical stem lacked cirri and was sometimes discarded, as in Edriocrinus, to produce a creeping adult. See also: Crinoidea; Echinodermata
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