Archenteron invagination and ingression of secondary mesenchymal cells.

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

Stage with three pairs of arms.

Post-oral arm tip in a six-arm pluteus larva.

Early stage with two arms (post-oral).

Early vestibule invagination in a six-arm stage.

Arm growing on an unusual site.

Early eight-arm stage.

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

Larva with six arms.

Oral region with the lantern of Aristotle in formation.

Oral region.

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

Arm growing on an unusual site.

Early eight-arm stage.

Oral region with the lantern of Aristotle in formation.

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

Aboral region (normal position).

Early with two arms.