The Echinoid Directory

 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).

Lower Cretaceous (Valanginian) to Recent; worldwide

 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

Gonzaleaster Sanchez Roig, 1952

Isopetalum Lambert, 1911

Mauritanaster Lambert, 1920

Nudobrissus Lambert, 1920

Pleraster Quenstedt, 1875

Proisaster Aziz & Badve, 2001
Pusillaster Lambert, 1920

Rovasendia Airaghi, 1901