Class Eocrinoidea ("dawn crinoids"). Eocrinoids existed between the Early Cambrian and Late Silurian periods. Class Eocrinoidea is the earliest known group of stalked,arm-bearing echinoderms. Eocrinoids were the most common echinoderms during the Cambrian. The eocrinoids were an experimental paraphyletic group within the echinoderms, that may have been ancestral to six other classes: Rhombifera, Diploporita, Coronoidea, Blastoidea, Parablastoidea, and Paracrinoidea. The earliest genera had a short holdfast and irregularly structured plates. Later forms had a fully developed stalk with regular rows of plates. The eocrinoids were sessile benthic suspension feeders. (Prothero,2004)
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