The Echinoid Directory

1a. Petals developed aborally.

1b. Apetaloid aborally or with weakly differentiated pore pairs.

2a. Apical disc with four gonopores.

2b. Apical disc with 3 gonopores (no opening in genital plate 2).

3a. Pore-pairs in frontal groove subpetaloid (dot-dash type pore-pairs).

3b. Pore-pairs in frontal groove small with an interporal node and differentiated from those in other ambulacra.

4a. Peristome opening faces forward; largely hidden by labral plate.

Micraster

4b. Peristome opening faces downwards; opening clearly visible in oral view.

5a.Petals short and narrow.

5b. Petals extend almost to ambitus; wide.

6a.Periproct opens below mid-height on short posterior face.

6b.Periproct opens above mid-height.