The earliest known crinoid groups date back to the Ordovician. Sea lilies are in fact animals, despite the appearance of being plants. They filter food from the surrounding water by the use of feeding arms. They live in both shallow water and in depths as great as 9,000 meters (30,000 ft). Those crinoids which, in their adult form, are attached to the sea bottom by a stalk.
Some fossil crinoids, such as Pentacrinites, seem to have lived attached to floating driftwood and complete colonies are often found. Sometimes this driftwood would become waterlogged and sink to the bottom, taking the attached crinoids with it. The stem of Pentacrinites can be several metres long. Modern relatives of Pentacrinites live in gentle currents attached to rocks by the end of their stem. The largest fossil crinoid on record had a stem 40 m (130 ft) in length.
Blastoids lived from the Ordovician to the Permian. Often called sea buds, blastoid fossils look like small hickory nuts. They first appear, along with many other echinoderm classes, in the Ordovician period, and reached their greatest diversity in the Mississippian sub period of the Carboniferous period. However, Blastoids may have originated in the Cambrian. Blastoids persisted until their extinction at the end of Permian, about 250 million years ago. Although never as diverse as their contemporary relatives, the crinoids, blastoids are common fossils