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The Echinoid Directory

Order Echinoneoida

Diagnosis

Clade of irregular echinoid with:

  • apical system tetrabasal, with four gonopores;
  • ambulacra flush, the five ambulacra identical; pores double throughout (except in a few highly paedomorphic forms); no buccal pores. Pore-pairs simple and undifferentiated in all but one taxon;
  • no differentiated perioral spines and tubercles; basicoronal interambulacral plate short, undifferentiated;
  • tuberculation uniform and undifferentiated;
  • lantern and perignathic girdle absent in adults.
Range Upper Jurassic (Oxfordian) to Recent, worldwide distribution.
Remarks This is the most primitive of the living groups of irregular echinoid. They are distinguished from clypeasteroids and cassiduloids by their undifferentiated ambulacra.