The Echinoid Directory

Acanthocidaris Mortensen, 1903, p. 21

Diagnostic Features
  • Test relatively tall with subvertical sides.
  • Apical disc about half test diameter; generally monocyclic; genital plate 2 a little larger than other genital plates. Uniformly covered in tubercles / spines.
  • Interambulacra with 9 plates in a series. Primary tubercles perforate and distinctly crenulate on adapical side, especially adapically; areoles not incised and separated except adjacent to the peristome where they become confluent.
  • Scrobicular circle strongly differentiated from extrascrobicular tubercles. Extrascrobicular zones not extensive but densely covered in rather uniform secondary tubercles.
  • No pits or naked zones.
  • Ambulacra sinuate; pore-pairs horizontal with the two pores separated by an interporal zone slightly wider than a pore. Pore-zone not sunken. Perradial zone similar in width to pore zone; with small marginal primary tubercles, but median zone largely naked and slightly depressed.
  • Primary spines long, tapering and facetted. Collar very broad and long (2-3 cm), ornamented with rows of nodes. Shaft rhomboidal in cross-section; with fine, linear ornament but appearing superficially smooth.
  • Oral spines curved and with serrated edges.
  • Secondary spines not much flattened and not strongly adpressed.
Recent, Indo-Pacific.
Name gender feminine
Cidaris curvatispinis Bell, 1892, p. 303, by original designation.
Species Included
  • A. curvatispinis (Bell, 1892); Recent, Mauritius.
  • A. hastigera Agassiz & Clark, 1907; Recent, Hawaii.
Classification and/or Status

Cidaroida, Cidaridae, Cidarinae.

Presumed monophyletic.


The highly characteristic spines immediately distinguish this taxon from all others. Spines of Porocidaris have a similar long tuberculate collar, but their shaft is flattened and its primary tubercles are coarsely tuberculate.

Mortensen, T. 1903. Danish Ingolf. Expedition 4(1), Echini, p. 21.

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