The Echinoid Directory

Key to the genera of Hemipneustidae

1a. Anterior petals poorly developed, with anterior and posterior columns of pore-pairs only weakly differentiated.

Plesiohemipneustes

1b. Anterior petals well developed, with anterior and posterior columns of pore-pairs extremely different in development.

Go to 2

2a. Aboral surface with coarse primary interambulacral tuberculation. Marginal fasciole may be present.

Opisopneustes

2b. Aboral surface without major tubercles. Marginal fasciole absent in adults.

Go to 3

3a. Test depressed with sharp ambitus. Frontal groove wide and deep, with walls converging anteriorly. Prominent paired nodes towards posterior on oral surface.

Toxopatagus

3b. Test inflated with ambitus near base. Frontal groove shallow and narrow. No oral nodes.

Hemipneustes