The Echinoid Directory

1a. Test ovate, without frontal groove.

1b. Test with sunken frontal ambulacrum.

2a. All five ambulacral zones weakly sunken.

2b. Only the frontal ambulacrum sunken.

3a. Interambulacra 2 and 3 rounded in aboral view.

3b. Sharp keels flanking the frontal groove.

4a. Subanal fasciole present, on oral side crossing interambulacral plates 5b4, 5a4 (marked as black line above).

4b. No subanal fasciole developed.

Go to 5

5a. Apical disc ethmophract; genital plates all in contact.

5b. Apical disc elongate, anterior pair of genital plates separated from posterior pair of genital plates by ocular plates II and IV.

6a.Hydropores scattered over all anterior plates of the apical disc. Labral plate tongue-like and projecting over peristome (opening appears crescentic).

Hemipneustidae

6b. Hydropores confined to genital plate 2. Labral plate not projecting.

7a. Marginal fasciole present around at least the posterior part of the test.

7b. No trace of a marginal fasciole.