Cystoids are extinct [[echinoderm]s that lived from the Ordovician Period until the Devonian Period. They lived attached to the sea floor by stalks, and were distinguished from other echinoderms by triangular pore openings.
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Cystoids are extinct [[echinoderm]s that lived from the Ordovician Period until the Devonian Period. They lived attached to the sea floor by stalks, and were distinguished from other echinoderms by triangular pore openings.