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The term "sand dollar" derives from the appearance of the tests (skeletons) of dead individuals after being washed ashore. The test lacks its velvet-like skin of spines and has often been bleached white by sunlight. To beachcombers of the past, this suggested a large, silver coin, such as the old Spanish dollar, which had a diameter of 38–40 mm.
Rotula deciesdigitatus from Sao Tomé. Rotulidae is a family of small sand dollars native to the Atlantic coast of Africa, with 3 genera, with Rotula and Heliophora being extant, the other, Rotuloidea, being extinct since the Pliocene, but all three being found in the fossil record along the Atlantic African coast since the Miocene.
Dendraster excentricus. Dendraster excentricus, also known as the eccentric sand dollar, sea-cake, biscuit-urchin, western sand dollar, or Pacific sand dollar, is a species of sand dollar in the family Dendrasteridae. It is a flattened, burrowing sea urchin found in the north-eastern Pacific Ocean from Alaska to Baja California.
Heliophora. Heliophora orbicularis, also known as the West African Sand Dollar, is a small sand dollar in to the family Rotulidae, and the only species in the genus Heliophora. It, and other members of Rotulidae have been found in West African marine strata from the Late Miocene onward. Like the related Rotula [nl], it is still extant.
Description. The tests (shells) of these sand dollars are round, flat and disc-like, typically measuring 3 inches (7.6 cm) in diameter. The entire shell is also covered with maroon-colored moveable spines. The color is a purplish brown, becoming bleached white when washed ashore. As in other echinoderms, five radial furrows branch from the ...
Clypeasteridae is a family of sea urchins in the order Clypeasteroida.This family was first scientifically described in 1835 by the Swiss-American biologist Louis Agassiz.. The clypeasteridae also known as the sand dollar, are round and semi-flat organisms with spines lining the underside of the body and elongated genital papillae aiding its survival and reproduction.
Keyhole sand dollar refers to five living species of sand dollars in the genus Mellita, plus the extinct †Mellita aclinensis.They are found on the Atlantic coasts of the Americas, ranging across the Caribbean Islands (e.g. Bermuda, Jamaica and Puerto Rico), from the southern United States at the north, to the southeastern coast of Brazil at the south.
Dendraster. L. Agassiz, 1847 [1] Dendraster is a genus of sand dollars of the family Dendrasteridae[2] within the order Clypeasteroida. The extant species in this genus are found in the northeast Pacific Ocean from Alaska to Baja California. [3] The best-known, most common and widespread species is D. excentricus. [3]