Protaxocrinus tuberculatus, crinoid fossil. Crinoids are marine organisms, most of which have long stalks anchored to the seabed, with five or more feathery arms radiating from a central disc. This specimen, dating from the Silurian period (440 million years ago), was discovered in the Wenlock Limestone formation of Dudley, Worcestershire, UK. It is part of the collections held at the Natural History Museum, London, UK.