Stage with three pairs of arms.

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

Early stage with only two arms (post-oral). Detail of the oral region where the antero-lateral arms are developing.

Four-cell stage.

Stage with four pairs of arms.

Aboral region (normal position).

Detail of teeth in the lantern of Aristotle.

Stage with three pairs of arms.

Lateral view.

Aboral surface (opposite to mouth).

Larva with four pairs of arms.

Zygote.

Aboral region.

Primary spine.

Lateral view.

Zygote.

Regression of larval tissues. Spicules of the larval skeleton are still present in the aboral region.

Embryos during early cellular divisions.

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

Lateral view showing the mesomeres.