Uintacrinus sp. fossil crinoid, illustration. Crinoids, or sea lilies, are marine echinoderms with five or more feathery arms radiating from a central disc. They use their arms to filter food from the water. Uintacrinus is unusual in that it didn't have a stalk to attach itself to the seafloor, and so probably floated freely. It lived around 90 to 83 million years ago in the Late Cretaceous.