All Things Sand Dollars

Live sand dollars are covered with many short, moveable spines that encompass their entire shell. Besides the special tube feet on their tops, sand dollars also have tube feet on their undersides. They use these feet to sift through the sand and catch tiny organisms. The tube feet pass the food along grooves that lead to the sea creature's mouth.

By the time the test washes up on the beach it is missing its velvety covering of minute spines and appears somewhat bleached from the sun. It is hard to believe it was once alive. Sand dollars are from the class of marine animals known as Echinoids, spiny skinned creatures. Their relations include the sea lily, the sea cucumber, the star fish and the sea urchin.

Sand dollars live beyond mean low water on top of or just beneath the surface of sandy or muddy areas. The spines on the somewhat flattened underside of the animal allow it to burrow or to slowly creep through the sand. Fine, hair-like cilia cover the tiny spines. These cilia, in combination with a mucous coating, move food to the mouth opening which is in the center of the star shaped grooves on the underside of the animal. Its food consists of plankters and organic particles that end up in the sandy bottom.

Due to their very small edible parts and relatively hard skeleton, few animals bother sand dollars. On the ocean bottom, sand dollars are frequently found together. This is due in part to their preference for soft bottom areas as well as convenience for reproduction. The sexes are separate and gametes are released into the water column as in most echinoids. The free-swimming larvae metamorphose through several stages before the test begins to form and they become bottom dwellers.

The spines on the somewhat flattened underside of the animal allow it to burrow or to slowly creep through the sand. Fine, hair-like cilia cover the tiny spines. Tubefeet or podia that line the food grooves, move food to the mouth opening which is in the center of the star shaped grooves on the underside of the animal called the oral surface. Its food consists of crustacean larvae, small copepods, detritus, diatoms, algae and organic particles that end up in the sandy bottom.

In 2008, scientists showed that sand dollar larvae can clone themselves as a mechanism of self defense. Larvae exposed to mucus from predatory fish cloned themselves, effectively halving their size. The smaller larvae are believed to better escape detection from fish predators, but may increase the danger of predation from smaller animals, such as crustaceans.

Click Wikipedia, Sand Dollar for more.