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Order Cidaroida Claus, 1880

Diagnosis	Regular echinoids with: test composed of 20 columns of plates; pairs of ambulacral columns alternating with pairs of interambulacral columns ambulacral plating simple or at most pseudocompound (i.e. every second or third element enlarged to accommodate a larger tubercle and spine, but individual elements not fused together by tubercle overgrowth) interambulacral plates dominated by a single large primary tubercle (except Tetracidaris which has two) perignathic girdle of interambulacral elements only (apophyses). ambulacral plates continuing as a series across the peristomial membrane teeth crescentic to U-shaped in cross-section; pyramids without a foramen magnum primary spines with external cortex (except in most primitive members) globiferous and tridentate pedicellariae only.
Range	Lower Permian to Recent; worldwide.
Type	Type genus Cidaris Leske, 1778,  p. 74,
Remarks	There is currently only a single order in the subclass Cidaroidea.  See Cidaroidea for key. The following taxon is spine-based and probably belongs here: Minicidaris Deraniyagala, 1961 Claus, C. F. W. 1880. Grundzuge der Zoologie. N. G. Elwertsche, Marburg & Leipzig. 1254 pp (4th edition).