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The mouth of the sand dollar is located on the bottom of its body at the center of the petal-like pattern. Unlike other urchins, the bodies of sand dollars also display secondary front-to-back bilateral symmetry with no morphological distinguishing features between males and females. The anus of sand dollars is located at the back rather than ...
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 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 , it is still extant.
Leodia sexiesperforata, commonly known as the six-holed keyhole urchin, [2] is a species of sand dollar, in the echinoderm order Clypeasteroida. It is native to tropical and sub-tropical parts of the western Atlantic Ocean where it buries itself in soft sediment in shallow seas.
The mouth is at the base of the animal and the anus at the top; the lower surface is described as "oral" and the upper surface as "aboral". [a] [2] Several sea urchins, however, including the sand dollars, are oval in shape, with distinct front and rear ends, giving them a degree of bilateral symmetry.
The tests (shells) of these sand dollars are round, flat and disc-like, typically measuring 3 inches (7.6 cm) in diameter. The growth rate for this animal is between 3.5 to 6 mm/yr in the latter 5 years of their lifespan, and the lifespan is typically around 8 years. [2]
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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.