The Echinoid Directory

Key to genera of Echinoida (2)

5a.Ambulacral plates trigeminate.

Go to 6

5b.Ambulacral plating polygeminate.

Go to 7

6a.Ambital interambulacral plate with single large primary tubercle. Test elongate along axis III-5.


6b.Ambital interambulacral plates with two subequal tubercles. Axis of test elongation unknown.


7a.4-8 pore-pairs to a plate, arranged as a simple arc. Primary and secondary spines cylindrical.


7b.8-18 pore-pairs to a plate, often crowded so as to form a double irregular column. Primary spines stout and facetted.

Go to 8

8a.Single large primary tubercle on all interambulacral plates.


8b.Interambulacral plates at ambitus and above with two or more subequal tubercles.

Go to 9

9a.Aboral spines stout and facetted, not forming a dense canopy; secondary spines not peg-like.


9b.Aboral spines forming a dense canopy.

Go to 10

10a.Aboral ambulacral plates with three equal tubercles. Aboral spines clavate.


10b.Single large primary tubercle on aboral ambulacral plates. Aboral spines tesselated.