Arbacioida are an

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

sea urchin Sea urchins () are spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin live on the seabed of every ocean and inhabit every depth zone from the intertidal seashore down to . The spherical, hard shells (tests) of ...

s, consisting of a single 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, all of the tubercles on their tests are of similar size. 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 : * '' Arbacia crenulata'' Kier, 1963 † (Miocene, east coast of USA) * '' Arbacia dufres ...

'' Gray, 1835 *''

Arbaciella ''Arbaciella'' is a genus of echinoderms An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollar ...

'' Mortensen, 1910a *'' 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 rec ...

, 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 *'' 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 {{Echinoidea-stub