Irregular echinoids with:
Early Jurassic (Pliensbachian) to Late Cretaceous (Maastrichtian); worldwide.
Holectypoids are primitive irregular echinoids that possess a functional jaw apparatus and have a large central peristome. The periproct opens orally in Holectypina, but aborally in Pygasterina. Cassiduloids differ in having a much smaller peristome and have pore-pairs crowded adorally to form phyllodes.