The Echinoid Directory

Key to the clades of Echinoneoida

1a. Apical disc includes complemental plates separating genital plates 1 and 4.

1b. Apical disc compact

Go to 2

2a.Periproct opening in direct contact with the apical disc.


2b.Periproct opening separated from the apical disc by several interambulacral plates.

Go to 3

3a.Ambulacra with simple plating throughout.


3b. Ambulacra with occluded plates (pyrinoid plating).

Go to 4

4a.Periproct marginal to inframarginal. Pore-pairs becone crowded into offset triads towards the peristome.


4b.Periproct oral. Pore-pairs uniserial to the peristome.