The Echinoid Directory

Key to genera of Echinoida (6)

26a.Ambulacra with 5 pore-pairs to each plate

Go to 27

26b.Ambulacra more than five pore-pairs to each plate

Go to 29

27a.Apical disc dicyclic. (Globiferous pedicellariae without muscular neck).

Paracentrotus

27b.Apical disc hemicyclic with posterior two ocular plates broadly insert. (Globiferous pedicellariae with muscular neck).

Go to 29

28a.Ambulacral zones narrow adorally, not as wide as interambulacral zones at peristome edge; test very thin; aboral plates rather naked, with fine granulation in addition to primary tubercles.

Allocentrotus

28b.Ambulacral zones at peristome broader than ambulacral zones; test robust; aboral plates strongly tuberculate.

Strongylocentrotus

29a.Ambulacral zones expanded adorally and wider than interambulacra.

Heliocidaris

29b.Ambulacral zones uniform in width adorally.

Go to 30

30a.Apical disc dicyclic.

Loxechinus

30b.Apical disc hemicyclic.

Strongylocentrotus