Fig. 1. Neural development during embryogenesis.

A. Proneural cells first appear in two locations, at the animal pole domain (ANE) (pink), and on either side of the ventral ectoderm (red). B. The ciliary band (blue) appears during gastrulation and shortly thereafter additional proneural cells appear. C. The cells in the ANE that become serotonergic neurons localize just dorsal to the ciliary band. The proneural cells in the ventral ectoderm become the postoral neurons and are both cholinergic and dopaminergic (red inside ciliary band), and ciliary band neurons appear in the ventral ectoderm and later differentiate in the ciliary band (red). In the gut, a set of enteric neurons (violet) are specified and later in the larval stage (D), these surround the mouth and the sphincters separating the chambers of the gut. E. A fluorescent image of a pluteus larva is stained with an antibody to L1, a pan-neural marker showing the entire nervous system plus the cell bodies of the skeletogenic cells (red). The nervous system is largely associated with the ciliary band (blue). Diagram after Garner et al., (2016).