Oral region with the lantern of Aristotle in formation.

Aboral surface (opposite to mouth).

Early with two arms.

Early eight-arm stage.

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

Oral region.

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

Aboral surface (opposite to mouth).

Stage with three pairs of arms.

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

Remnants of the larval skeleton in the aboral region of the juvenile.

Stage with four pairs of arms.

Ring of mesenchyme cells beginning to secrete the calcareous skeleton.

Early stage with two arms. Detail of a post-oral arm.

Aboral surface (opposite to mouth).

Fork which originates the pre-oral arms.

Anal region of the larva with six arms.

Detail of the mesenchymal cells secreting the larval skeleton on an early pluteus stage.