Mellitidae - Sand Dollars
Sand dollars, or keyhole urchins, are members of the Phylum Echinodermata, which also includes starfishes and brittle stars, sea urchins, sea cucumbers, and feather stars. Sand dollars are round, flat and rigid with no arms. Like starfishes and brittlestars, they have no anterior, posterior, head or tail. Adult sand dollars have five oval-shaped holes that go all the way through the body. The top surface also has five pairs of pores called petalloids. The pairs are arranged in the shape of a five-petal flower. Within the petalloids are specialized tube feet that are used for respiration.
When live, sand dollar bodies are covered with small spines, and they are usually green, brown, tan or gray in color. After death, their spines fall off exposing their off-white skeletons. This is how they are usually found washed ashore on beaches. Their mouth, on the underside of body, has a set of five jaws with teeth. The arrangement of the jaws is called "Aristotle's lantern", which is also common in most sea urchins. Beachcombers who find the jaws from broken sand dollars often refer to them as "doves" because they resemble a bird in flight.