Early eight-arm stage, lateral view.

Lateral view showing the mesomeres.

Structure in the anal region.

Aboral surface (opposite to mouth).

Detail of the vestibule near the left coelom and the central gut during early eight-arm stage.

Aboral region (normal position).

Stage with three pairs of arms.

Early with two arms.

Polarized light highlights the calcareous skeleton showing the structure of spines, podia, and remnants of the larval skeleton.

Archenteron during invagination.

Blastopore and ring of mesenchyme cells secreting the larval skeleton.

Larva with six arms.

Stage with four pairs of arms.

Stage with four pairs of arms.

Stage with three pairs of arms.

Growth of antero-lateral pair of arms (2nd pair).

Oral region with the lantern of Aristotle in formation.

Detail of vestibule invagination.

Stage with three pairs of arms.

Detail of teeth in the lantern of Aristotle.