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The term Crinoid refers to an extant (living) class of Echinoderms. These animals, commonly known as “sea lillies” and “feather stars”, have a long history. They first appear in the fossil record in marine sediments deposited around 530 million years ago during the Cambrian period. Stemmed forms are called sea lillies because of their superficial resemblance to flowers. These stemmed crinoids became abundant in the middle Ordovician period, 470 million years ago, and flourished in the shallow inland seas of the Paleozoic Era. Though so abundant that many late Paleozoic limestone deposits are composed primarily of Crinoid skeletal parts, they nearly became extinct 240 million years ago at the end of the Paleozoic Era.
Note: up to the mid 1970′s Crinoids were thought to be extinct, but while deep diving in the Pacific Ocean checking out underwater volcanic activity a massive colony of very large size Crinoids were discovered