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The Echinoid Directory

Order Spatangoida L. Agassiz, 1840, p. 15

[= Atelostomata Lambert, 1893, p. 63]

Diagnosis	Irregular echinoids with: distinct bilateral symmetry along the plane III-5, with mouth displaced anteriorly on the lower surface and the periproct marginal to submarginal compact apical disc with ocular plates II and IV separated posterior interambulacrum on oral surface differentiated to form labrum one plate in each ambulacral zone bordering the mouth with two tube-feet (and pores).
Range	Lower Cretaceous (Valanginian) to Recent; worldwide
Remarks	Spatangoids are one of the most diverse of extant echinoid orders. They share with holasteroids the differentiation of the posterior interambulacrum into a plastron and the presence of two tube-feet on one of the plates bordering the peristome in each ambulacral zone. The two groups are easily distinguished however, by their apical disc structure. In spatangoids ocular plates II and IV are small and separated from one another by genital plates, whereas in holasteroids ocular plates II and IV are large and abut. The following genera remain too poorly known to place at present into any family: Adetaster Lambert, 1895 Cheopsia, Fourtau, 1909 Enichaster de Loriol, 1882 Mauritanaster Lambert, 1920 Rovasendia Airaghi, 1901

Diagnosis

Irregular echinoids with:

distinct bilateral symmetry along the plane III-5, with mouth displaced anteriorly on the lower surface and the periproct marginal to submarginal
compact apical disc with ocular plates II and IV separated
posterior interambulacrum on oral surface differentiated to form labrum
one plate in each ambulacral zone bordering the mouth with two tube-feet (and pores).

Range

Lower Cretaceous (Valanginian) to Recent; worldwide

Remarks

Spatangoids are one of the most diverse of extant echinoid orders. They share with holasteroids the differentiation of the posterior interambulacrum into a plastron and the presence of two tube-feet on one of the plates bordering the peristome in each ambulacral zone. The two groups are easily distinguished however, by their apical disc structure. In spatangoids ocular plates II and IV are small and separated from one another by genital plates, whereas in holasteroids ocular plates II and IV are large and abut.

The following genera remain too poorly known to place at present into any family:

Adetaster Lambert, 1895
Cheopsia, Fourtau, 1909

Enichaster de Loriol, 1882

Mauritanaster Lambert, 1920

Rovasendia Airaghi, 1901