The Echinoid Directory

Key to the subfamilies of Cidaridae

1a. Primary tubercles weakly but consistently crenulate.
Plegiocidaris (stem group plesion)

1b. Primary tubercles non-crenulate or with traces of crenulation only on adapical side of aboral tubercles.

Go to 2

2a. Interambulacral plates without clearly differentiated scrobicular tubercles.


2b. Interambulacral plates with ring of scrobicular tubercles clearly differentiated.

Go to 3

3a. Interambulacral zones have one or more of the adapical plates lacking a functional tubercle.


3b. All fully formed adapical plates in the interambulacral zones with functional tubercles.

Go to 4

4a. Interradial zone without pits or well defined naked zone.


4b. Interradial zone with pitted or naked interradial zone.