Crinoid Crinoids are members of the same family as starfish, sand dollars, and sea urchins. They may still be found today, although, they were most abundant in Paleozoic times. Some limestones are completely made of crinoid fragments. Crinoids attached themselves to the seafloor by their roots.
Arms extend upwards from the calix.
The long flexible stem allows the crinoids to bend and wave in the ocean currents. Crinoids live i warm shallow seas. Round coin like pieces of crinoid stem are commonly found at Arkona.