Keyhole sand dollar
 | It has been suggested that this article be merged into Sand_dollar. (Discuss) Proposed since May 2007. |
| Keyhole sand dollar | |
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| Mellita quinquiesperforata | |
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| Family: | Mellitidae Leske, 1778
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| Genus: | Mellita
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Keyhole sand dollar refers to three species of sand dollar in the genus Mellita that are dispersed along the east coast of the United States from Virginia to Brazil and also found along the coasts of Bermuda, Jamaica, and Puerto Rico. Mellita isometra is found along the east coast of the United States, Mellita tenuis is found is found along the gulf side of Florida, Alabama, and Mississippi. Mellita quinquiesperforata is found from near the Mississippi Delta to Brazil.
Keyhole sand dollar is found in shallow waters below tide lines in sandy bottoms, burrowing for protection from waves and predators, and to obtain food. They feed on fine particles of organic matter they filter from the water.
Sand dollars are flat versions of sea urchins, reaching up to three inches in diameter and disk-like in shape. They differ greatly from their closely related cousin, however: the underside is usually flat or concave with the mouth directly in the center and the anus to one side. Its mouth is made up of five teeth arranged in a circle that form what is called, "Aristotle's lantern". Its skeleton is called a test and covered with an epidermis, spines (used in burrowing), tube feet (used for locomotion), and cilia. On its upper surface, petalloids (used as gills), specialized tube feet, are arranged in a pattern favoring five flower petals. Five oval shaped holes, called lunules, pierce the tests in keyhole urchins. There are two pairs of lunules, one pair toward the top and one large longer hole in between the second pair toward the bottom.
Coloration of the keyhole sand dollar varies, including tan, brown, and occasionally grayish or green hue.
The Sand dollar pass through several life stages. After eggs have been fertilized they develop into swimming larvae. They drift in the sea water as plankton for four to six weeks, filtering tiny organisms. Juvenile keyhole urchins grow into adults, and live on the ocean floor.
Natural enemies of the keyhole sand dollar are starfish, flounder, haddock, cod and other bottom feeding fishes.
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Mouth and anus located in center underside of sand dollar. -
Hundreds of tube feet, called podia on underside work in unison for locomotion.
References
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