Wiktionary
cystoids
n. (plural of cystoid English)
Wikipedia
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.