Fig. 4

Cartoons showing the morphology of gastrula, auricularia, doliolaria and pentactula larvae. In the gastrula, mesenchymal cells migrate from the archenteron (future gut) while it elongates anteriorly. The first neurons appear at this stage. Auricularia larvae are characterized by a functional digestive system, the presence of the hydrocoel, the left and right somatocoels and hyaline spheres. At this stage, the nervous system increases in complexity. Doliolaria is a transitional barrel-shaped larva that does not feed. It has larger hyaline spheres compared to the auricularia. Adult organs are formed in the pentactula, the last stage before the juvenile. In figure, a green continuous line indicates the neurons underneath the ciliary band. To make the auricularia cartoon clearer and show distribution of neurons we omitted the ciliary band that follows the same pattern