Arbacioida
Introduction '''Arbacioida''' are an order of sea urchins, 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, all of the tubercles on their tests are of similar size.Genera:*''Arbacia'' Gray, 1835*''Arbaciella'' Mortensen, 1910a*''Arbia'' Cooke, 1948†*''Baueria'' Noetling, 1885†*''Codiopsis'' Agassiz, in Agassiz & Desor, 1846†*''Coelopleurus'' Agassiz, 1840a*''Cottaldia'' Desor, 1856 †*''Dialithocidaris'' Agassiz, 1898*''Habrocidaris'' Agassiz & Clark, 1907b*''Hattopsis'' *''Podocidaris'' Agassiz, 1869*''Pygmaeocidaris'' Döderlein, 1905*''Sexpyga'' Shigei, 1975*''Tetrapygus'' Agassiz, 1841b
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