Crinoids are known as sea lilies because they live on a stem and have a flower-like body. They are analogous to starfish with a stem. Although still existing but uncommon in the oceans today, they were very abundant in shallow tropical seas during the Paleozoic. Some Mississippian rocks contain so many broken-up fossil crinoids that the Mississippian became known as the Age of Crinoids. The most common crinoid fossils are the individual button-like plates that made up the stem. Crinoid fossils can be found in the Ordovician, Silurian, Devonian, Mississippian, and Pennsylvanian rocks of Kentucky.