The Echinoid Directory

Key to major clades of Holasteroida

1a. Plastron plating protosternous at least in juveniles (may become quasi-metasternous).
Basal holasteroids

1b. Plastron plating either meridosternous or metasternous - i.e. labral plate followed by a single sternal plate.

Go to 2

2a. Episternal and subsequent plates biserially arranged.


2b. Plastron plating metasternous.