Fossil crinoids (Pentacrinus fossilis). Rock containing crinoid, or sea lily, fossils. This fossil dates from the Late Jurassic period (between 161 and 145 million years ago). Crinoids are marine echinoderms that have been in existence for 500 million years. Thousands of extinct crinoid species have been found as fossils, but only a few hundred species still exist today. They attach themselves to the sea floor with their stem and use their feathery arms to filter food from the water. This specimen was found in Dorset, UK.