The Echinoid Directory

• Test relatively thick; flattened above and below.
• Apical disc about half the test diameter. Generally monocyclic. Plates uniformly covered in dense granules. All five genital plates similar in size.
• Interambulacrum with 6-9 plates in a series. Primary tubercles perforate, non-crenulate. Areoles circular and incised; scrobicular circles separated except adorally.
• Scrobicular tubercles differentiated. Extrascrobicular areas not extensive; densely and uniformly covered in secondary tubercles.
• No sutural furrows or pits.
• Ambulacra weakly sinuous. Pore-pairs non-conjugate with narrow interporal partition; pore zones sunken. Perradial zone with marginal series of contiguous primary tubercles and inner series of smaller tubercles.
• Peristome smaller than apical disc. Ambulacral plates uniserial; interambulacral series extending to the mouth.
• Primary spines long, cylindrical, with short collar and neck; ornamented with relatively fine serrated ribs. Secondary spines adpressed.

Recent, Atlantic.

Echinus cidaris Linneus, 1758, p. 664, by subsequent designation of Mortensen, 1910, p. 118.

• C. cidaris (Linnaeus, 1758); Recent, North Atlantic.
• C. abyssicola (Agassiz, 1869): Recent, West Atlantic.
• C. rugosa (Clark, 1907); Recent, West Atlantic and West Indies.
• C. blakei (Agassiz, 1878); Recent, West Indies.
• C. nuda (Mortensen, 1903); Recent, Cape Verde.

Cidaroida, Cidaridae, Cidarinae.

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Many fossils have been assigned to this genus without justification. In test morphology Cidaris can be distinguished from the closely related Tretocidaris and Lissocidaris by the narrowness of the partition between pores of each pore-pair. Eucidaris has subconjugate pore-pairs and also has pore-pairs on the peristomial membrane that become biserial distally. Tretocidaris further differs in having no end tooth on its globiferous pedicellariae and a more notched apical disc outline.

Cidarites has been a name applied to fossils to distinguish them from extant members of that taxon. It is not a valid taxon name.

Clark, H. L. 1909. The Cidaridae. Bulletin of the Museum of Comparative Zoology at Harvard College 51(7), 165-230, pls 1-11.

Leske, N. G. 1778. Jacobi Theodori Klein naturalis dispositio echinodermatum . . ., edita et descriptionibus novisque inventis et synonomis auctorem aucta.  Addimenta ad  I. T. Klein naturalem dispositionem Echinodermatum, xxii + 278 pp. 54 pls. G. E. Beer, Leipzig.

Mortensen, T. 1928. A monograph of the Echinoidea. 1, Cidaroidea. C. A. Reitzel, Copenhagen.