Crinoids are commonly known as sea lilies, though they are animals, not plants. Crinoids are echinoderms related to starfish, sea urchins, and brittle stars. Most of the Paleozoic crinoid species attached themselves to substrates on the ocean floor. Crinoids are famous for their feathery, tentacle-like appendages that opened up like a flower and captured particles of food such as plankton. Though crinoids appeared in the Ordovician they survived the Permian mass extinction and diversified into hundreds of species which survive today.