Detail of the gut.

Blastula.

Early eight-arm stage. Well developed vestibule in contact with the left coelom.

Blastula.

Spines.

First cleavage

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

Oral region with the lantern of Aristotle in formation.

Larva with four pairs of arms.

Larva with six arms.

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

Larva with three pairs of arms.

Lateral view of mesomeres.

Oral region with the lantern of Aristotle in formation.

Zygote.

Frontal view of a two-arm larva.

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

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