Cidaroida
Introduction '''Cidaroida''' is an order of primitive sea urchins, the only living order of the subclass Perischoechinoidea. All other orders of this subclass, which were even more primitive than the living forms, became extinct during the Mesozoic.
Description Their primary spines are much more widely separated than in other sea urchins, and they have no buccal slits. Other primitive features include relatively simple plates in the test, and the ambulacral plates continuing as a series across the membrane that surrounds the mouth.
Families Many different fossil cidaroid radiola (spines) at the MNHNAccording to World Register of Marine Species: * family Anisocidaridae Vadet, 1999 †* superfamily Cidaroidea Gray, 1825** family Cidaridae Gray, 1825** family Ctenocidaridae Mortensen, 1928a** family Paurocidaridae Vadet, 1999a †* family Diplocidaridae Gregory, 1900 †* family Heterocidaridae Mortensen, 1934 †* superfamily Histocidaroidea Lambert, 1900** family Histocidaridae Lambert, 1900** family Psychocidaridae Ikeda, 1936* family Miocidaridae Durham & Melville, 1957 †* family Polycidaridae Vadet, 1988 †* family Rhabdocidaridae Lambert, 1900 †* family Serpianotiaridae Hagdorn, 1995 †* family Triadocidaridae Smith, 1994c †Image:Stylocidaris affinis.jpg|''Stylocidaris affinis'' (Cidaridae)Image:Notocidaris.jpg|''Notocidaris sp.'' (Ctenocidaridae)Image:Histocidaris variabilis.jpg|''Histocidaris variabilis'' (Histocidaridae)Image:Tylocidaris ohshimai.JPG|''Tylocidaris ohshimai'' (Psychocidaridae) Image:Miocidaris coaeva MHNT.PAL.2006.94.jpg|''Miocidaris coaeva'' (Miocidaridae, fossil)Image:Paracidaris florigemma.JPG|''Paracidaris florigemma'' (Polycidaridae, fossil)Image:Cidaris blakei.jpg|''Cidaris blakei'', abyssal Caribbean speciesImage:Eucidaris tribuloides (Slate-pencil Urchin).jpg|''Eucidaris tribuloides'', shallow Caribbean speciesImage:Phyllacanthus.jpg|''Phyllacanthus imperialis'', shallow Indo-Pacific speciesImage:Plococidaris verticillata.jpg|''Plococidaris verticillata'', rare shallow Indo-Pacific speciesImage:Prionocidaris baculosa.jpg|''Prionocidaris baculosa'', from PhilippinesImage:Reef0228.jpg|''Chondrocidaris gigantea'', from Hawaii
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