Crinoids are odd little critters, for sure. Often called “living fossils,” they’re rarely seen alive as their modern counterparts live at ocean depths exceeding 100 meters (and more often 200 meters). You’re more likely to see a crinoid fossilized in a block of stone, as is the case of this 322 million year old slab on display at the New Mexico Museum of Natural History and Science in Albuquerque, New Mexico:
While they look somewhat like plants, crinoids are definitely animals, related to modern-day sea stars and sand dollars. Crinoids are filter feeders, capturing whatever small bits of food drift by them — here their stalks attached them to the sea floor, and the flowery / feathery looking parts contained their mouths.
While crinoids are hardly extinct, they hold nothing like the dominant position they once had on the ocean floor. At the end of the Permian period, some 250 million years ago, the crinoids suffered a near-total extinction (along with many other species).