Cidaroida[1] 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.
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.
According to World Register of Marine Species:[1]
Notocidaris sp. (Ctenocidaridae)
Miocidaris coaeva (Miocidaridae, fossil)
Paracidaris florigemma (Polycidaridae, fossil)
Cidaris blakei, abyssal Caribbean species
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Eucidaris tribuloides, shallow Caribbean species
Phyllacanthus imperialis, shallow Indo-Pacific species
Plococidaris verticillata, rare shallow Indo-Pacific species
Prionocidaris baculosa, from Philippines
Chondrocidaris gigantea, from Hawaii
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.
