Close up on the pair of posterior spines (longer).

Early with two arms.

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

Primary spine.

Skeleton formation of post-oral arms.

Oral region.

Aboral surface (opposite to mouth).

Larva with two pairs of aarms and early development of postero-dorsal arms on the body sides.

Larva with four pairs of arms.

Ossicles of the lantern of Aristotle in formation at the oral region.

Early stage with two arms (post-oral).

Early stage with two arms (post-oral).

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

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

Aboral surface (opposite to mouth).

Oral region with the lantern of Aristotle in formation.

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

Mouth, esophagus, gut and vestibule invagination (larva left side) during six-arm stage. Anal view.

Early stage with two arms showing cells with pigmented granules in the epithelium.

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