Arbacioida are an

order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...

sea urchin Sea urchins or urchins () are echinoderms in the class (biology), class Echinoidea. About 950 species live on the seabed, inhabiting all oceans and depth zones from the intertidal zone to deep seas of . They typically have a globular body cove ...

s, consisting of a single extant family, the Arbaciidae. They are distinguished from other sea urchins by the presence of five separate plates around the anus. Unlike their close relatives, the

Salenioida The Salenioida are an order of sea urchins. Description and characteristics They are distinguished from other sea urchins by the presence of a large plate on the upper surface, with the anus to one side. They have very large tubercles between t ...

, all of the tubercles on their tests are of similar size. This order includes about 50 species (roughly 24 extant) divided into 14 genera: *''

Arbacia ''Arbacia'' is a genus of sea urchins, widespread in the Atlantic and eastern Pacific oceans. Species According to the World Register of Marine Species this genus includes the following species: * '' Arbacia abiquaensis'' Linder, Durham & Orr, ...

'' Gray, 1835 *''

Arbaciella ''Arbaciella'' is a genus of echinoderms An echinoderm () is any animal of the phylum Echinodermata (), which includes starfish, brittle stars, sea urchins, sand dollars and sea cucumbers, as well as the sessile sea lilies or "stone lil ...

'' Mortensen, 1910 *'' Arbia'' Cooke, 1948† *'' Baueria'' Noetling, 1885† *'' Codiopsis''

Agassiz Jean Louis Rodolphe Agassiz ( ; ) FRS (For) FRSE (May 28, 1807 – December 14, 1873) was a Swiss-born American biologist and geologist who is recognized as a scholar of Earth's natural history. Spending his early life in Switzerland, he recei ...

, in Agassiz & Desor, 1846† *''

Coelopleurus ''Coelopleurus'' is an extant genus of echinoids with fossil records dating back to the Eocene, with remains found in Europe and North America. Characteristics These abyssal sea urchins are characterized by their surprisingly bright color pat ...

, 1840a *'' Cottaldia'' Desor, 1856 † *'' Dialithocidaris''

, 1898 *'' Habrocidaris''

& Clark, 1907b *''

Hattopsis ''Hattopsis'' is a genus of echinoid in the family Arbaciidae. It was described in 1992 from specimens in the UAE. There were 2 species described, though one was moved to another genus: ''Hattopsis paucituberculatus'' (now in genus '' Noetlingas ...

'' *'' Podocidaris''

, 1869 *'' Pygmaeocidaris'' Döderlein, 1905 *'' Sexpyga'' Shigei, 1975 *''

Tetrapygus ''Tetrapygus'' is a genus of sea urchins in the family Arbaciidae. It is a monotypic genus and the only species is ''Tetrapygus niger'' which was first described by the Chilean naturalist Juan Ignacio Molina in 1782. It is found in the southeas ...

, 1841b

References

* * Extant Middle Jurassic first appearances Echinoderm orders {{Echinoidea-stub