Crinoid

Crinoids or “sea lilies” were a group of echinoderms with a cup shaped body and 5 or more feathery arms. They were attached to the sea floor by a flexible stem of disc-like plates that were circular or pentagonal. The cup of the crinoid was also made up of a series of loosely connected plates. The cup and stem usually fell apart after death, so fossils are most often found as segments. It is rare to find a complete fossil. Crinoid skeletal components are made of calcite and fossilize well. Crinoids evolved rapidly into a large number of now extinct species. Because of this, they are considered a good index fossil for dating rocks, particularly those in the Paleozoic Era.