One of our oldest fossils, crinoids have lived in oceans since at least the Ordovician Era (485 million years ago). These echinoderms flourished in the Paleozoic Era, covering the ocean floor with their feathery appendages that would open up like a flower to capture food particles like plankton.
They survived the Permian Period, which ended with the largest mass extinction event in history. Crinoids went on to diversify into hundreds of varieties, most famously the sea lily and feather star inhabiting oceans today.
The crinoid, like its fellow echinoderms, has tube feet, radial symmetry, and a water vascular system. These fossils have been found in large limestone deposits through North America and Europe.
Crinoids are marine animals that make up the class Crinoidea, one of the classes of the phylum Echinodermata, which also includes the starfish, brittle stars, sea urchins and sea cucumbers. Those crinoids which, in their adult form, are attached to the sea bottom by a stalk are commonly called sea lilies, while the unstalked forms are called feather stars or comatulids, being members of the largest crinoid order, Comatulida.
Adult crinoids are characterised by having the mouth located on the upper surface. This is surrounded by feeding arms, and is linked to a U-shaped gut, with the anus being located on the oral disc near the mouth. Although the basic echinoderm pattern of fivefold symmetry can be recognised, in most crinoids the five arms are subdivided into ten or more. These have feathery pinnules and are spread wide to gather planktonic particles from the water. At some stage in their life, most crinoids have a stem used to attach themselves to the substrate, but many live attached only as juveniles and become free-swimming as adults.
There are only about 600 living species of crinoid, but the class was much more abundant and diverse in the past. Some thick limestone beds dating to the mid- to late- Paleozoic era are almost entirely made up of disarticulated crinoid fragments.
Large Crinoid Fossil