Sand dollars are in the Echinoid (Echinoderms) class of marine animals. When alive, they are covered with a suit of moveable spines that encompass the entire shell. Like its close relative the sea urchin, the sand dollar has five sets of pores arranged in a petal pattern. The pores are used to move sea water into its internal water-vascular system, which allows for movement.
The name “sand dollar” is a reference to their round flat shape, which is similar to a large coin. Sand dollars usually eat tiny particles of food that float in the water. They hide by burying themselves under the sand.
The term “sand dollar” can also refer to the skeleton or test left when a sand dollar dies. By the time the test washes up on the beach, it is usually missing its velvety covering of minute spines and has a somewhat bleached appearance due to its exposure to the sun. There is even a Legend of the Sand Dollar. they are popular ornaments around Christmas and Easter because of the legend.