The Echinoid Directory

Diadematoida with:

• test depressed; coronal plating rigid to slightly flexible especially adapically
• apical disc relatively small; generally hemicyclic with posterior oculars insert; genital plates strongly projecting interradially. Periproctal plating well-developed peripherally
• ambulacral plating trigeminate, with an enlarged element and two smaller demiplates
  
• pore-pairs uniserial; arranged into weak arcs. May become crowded adorally to form phyllodes
• interambulacral plates usually with multiple subequal tubercles forming a row. If one, then adradial and interradial zones well developed and with secondary tubercles
• sphaeridial pit close to every third pore-pair from peristome to apex
• tubercles perforate and almost always crenulate
• peristome small; buccal notches rounded, with associated tags. Perradial notch also present
• spines verticillate and hollow or with sparse open mesh
• larva with just two arms.

Lower Cretaceous (Aptian) to Recent; worldwide.