Cidaroida

Cidaroida Temporal range:
Scientific classification
Kingdom:	Animalia
Phylum:	Echinodermata
Class:	Echinoidea
Subclass:	Perischoechinoidea
Order:	Cidaroida Claus, 1880
Families
Cidaridae Psychocidaridae

Cidaroida is an order of primitive sea urchins, the only living order of the subclass Perischoechinoidea. All other orders of this subclass became extinct during the Mesozoic, and were even more primitive than the living forms.

Their primary spines are much more widely separated than in other sea urchins, and they have no gills. 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.

References

• Barnes, Robert D. (1982). Invertebrate Zoology. Philadelphia, PA: Holt-Saunders International. p. 980. ISBN 0-03-056747-5.
• National History Museum. "Cidaroida". Retrieved 20th Dec 2009. {{cite web}}: Check date values in: |accessdate= (help)