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.