The Echinoid Directory

Order Echinoneina H. L. Clark, 1925

Diagnosis

Clade of Neognathostomata with:

  • apical system tetrabasal, with four gonopores;
  • ambulacral pores double throughout (except in a few highly paedomorphic forms); no buccal pores;
  • peristome oblique (long axis 2-V); without invaginated, well-like entrance;
  • differentiated perioral spines and tubercles absent; basicoronal plate short, undifferentiated;
  • tuberculation uniform and undifferentiated.
Range
Early Cretaceous (Valanginian) to Recent, worldwide distribution.
Remarks
This is the most primitive of the living groups of irregular echinoid. They are distinguished from clypeasteroids and most cassiduloids by their oblique peristome and (with one exception) their lack of petals.