High Quality Content by WIKIPEDIA articles! 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 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.