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Sand dollars diverged from the other irregular echinoids, namely the cassiduloids, during the early Jurassic, [5] with the first true sand dollar genus, Togocyamus, arising during the Paleocene. Soon after Togocyamus, more modern-looking groups emerged during the Eocene. [1] Sand dollars are small in size, averaging from 80 to 100 mm (3 to 4 ...
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.
These sand dollars were originally named Echinodiscus emarginatus, [9] but have since been transferred to the Encope genus within the Mellitidae family. [6] Encope is thought to be the most diverse genus among sand dollars, containing 7 extant species. [1] Fossils can be dated back to the Pliocene or Pleistocene, up to 5 million years ago. [1]
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.
Echinarachnius parma, the common sand dollar, is a species of sand dollar native to the Northern Hemisphere. [1] ... On the species of the Linnean genus Echinus ...
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.
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 .