Sand dollars (order Clypeasteroida) are flat, round marine animals related to sea urchins (echinoids), sea stars, and other echinoderms. A sand dollar has a rigid skeleton, or test, and the term sand dollar also refers to this test when it is found as a sand dollar's remains. When sand dollars are living, they have a skin of moveable spines covering the entire test. Like its close relative the sea urchin, the sand dollar has a set of five pores arranged in a petal pattern. The pores are used to move sea water into its internal water-vascular system which allows the creature to move.
The name "sand dollar" is a reference to its round flat shape, which is similar to a large coin. The term "sand dollar" can also refer to the 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 and often slightly greenish appearance due to its exposure to the sun.
On the ocean bottom, sand dollars are frequently found together. This is due in part to their preference for soft bottom areas, which are convenient for their reproduction. The sexes are separate and, as with most echinoids, gametes are released into the water column. The free-swimming larvae metamorphose through several stages before the skeleton or test begins to form, and they become bottom dwellers.
[via: http://en.wikipedia.org]
Sand Dollar
Photo by wildcat_dunny
Time Lapse of a Sand Dollar at Pismo Beach California
The Legend Of The Sand Dollar
