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cystoids

n. (plural of cystoid English)

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Cystoids

Cystoidea or cystoids, is a class of extinct echinoderms in the sub-phyla Blastozoa, that lived attached to the sea floor by stalks.

They existed during the Paleozoic Era, in the Middle Ordovician and Silurian Periods, until extinction in the Devonian Period.