In addition to sea urchins, the Class Echinoidea contains animals known as sand dollars that have flattened bodies encased in closely fitted endoskeletal plates. Sand dollars are usually found on soft bottoms where they burrow through sand and marine deposits in search of food. They feed by filtering fine organic matter through a dense covering of spines, which are very small and used for locomotion through the sand.  In sand dollars, the mouth is located on the oral surface and the anus is located off to one side of the animal.