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What Is A Sand Dollar ?

By the time the sand dollar washes up on the beach, it's missing it's velvety covering of minute spines, and appears somewhat bleached from the sun. The fragile disk is the skeleton or 'test' of a marine animal. It's hard to believe it was once alive.
Sand dollars are from the class of marine animals known as Echinoids, spiny skinned creatures. Their relatives include the sea lily, sea cucumber, star fish, and sea urchin. When alive, the local species, Echinarachnius parma, is  a purplish maroon color 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 it's internal water vascular system, which allows for movement. Also sand dollars have suckers which are fueled by water pressure. The suckers help the sand dollar slide into the sand to get away from predators
Sand dollars live in 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.
The surface of the sand dollar appears to have petal patterns, which are really tube feet used for respiration. These tube feet combines with mucous coated cilia, and it catches food that is favored by the sand dollar. Some of these foods are cod, haddock, plankter, and organic particles. The sand dollar likes to mainly feed on small worms and algae. The sand dollars eat the food, by consuming it on the underside of itself, and with a set of five teeth, chew and swallow its food. These mouths are much like a bird beak because it can be used to scrape things like algae off of rocks.
The sand dollar has many predators. Sand dollars have no way to protect themselves, except for camouflaging themselves in the few inches of sand they are under. Their main predators are starfish, birds, otters, flounder, crustaceans, and octopus. Sometimes, crabs cause damage, because they nip at the sand dollar, and with their claws. Sometimes, it will eat or attack the sand dollar, and then leave it  alone, to die.
Sand dollars also die from heavy storms. When severe storms hit, sand is shifted all around, which can bury a sand dollar in 12 inches of sand. This disables the sand dollar, and it cannot escape. Another mass mortality is, from high temperatures. Sand dollars can survive in water that is 95°F for only three hours.
One type of sand dollar, is called the keyhole urchin, or the keyhole sand dollar.  On the keyhole sand dollar, there are 5 shaped slots, that look just like a keyhole. This feature gives the keyhole sand dollar, its name. The skeleton is rarely found on some beaches. Once the tan urchin dies, the spine will fall off, and the skeleton is bleached white. Many times, dead sand dollars are found, but they are chipped. These urchins, just like other sand dollars, live on the tide line, where they can burrow deep into the sediment.
On the ocean bottom, sand dollars are frequently found together. This is due in part to their preference of 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 eggs are fertilized by the moving currents. They develop into tiny swimming larvae. After a month, the larvae sink to the bottom, and then start to grow a protective shell.
One type of sand dollar is called the keyhole urchin, or the keyhole sand dollar. It is related to a normal, plain sand dollar. On the keyhole sand dollar, there are 5 shaped slots that look just like a keyhole. This feature gives the keyhole sand dollar its name. The skeleton is rarely found on some beaches. Once the tan urchin dies, the spine will fall off, and the skeleton is bleached white. Many times dead sand dollars are found but they are chipped. These urchins, just like other sand dollars, live on the tide line where they can burrow deep into the sediment.
You can find dead sand dollars on the beach after they have been washed ashore. People, for hundreds of years, wear the fossil of sand dollars as jewelry, or use them in various arts and crafts.
Since the sand dollar lives in sandy locations, anyone who would like to collect their shells, should comb beaches as the tide recedes. The very best time for collecting, is after a heavy storm, as many of the shells that have died, are dredged up by the increased wave action.

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