Schematic representation of the left side of amphioxus larva showing the expression of miRNAs in CNS and PNS. Above the figure the putative territories homologous to the vertebrate diencephalon (D), midbrain (M), hindbrain (HB) and spinal cord (SC) are reported. The expression of miRNAs are shown by colored boxes. Different color shades of boxes indicate different stages of development in which we observed the appearance of new expression domains (light green correspond to the expression of miR-124 up to larva with a first gill and dark green miR-124 expression at larva with 3-4 gill slits; light yellow indicates miR-137 expression until 48 hour larva and dark yellow miR-137 expression at 72 hour larva). miR-7 and miR-183 transcripts in the preoral organ and epidermal sensory cells of PNS (red spots and pink triangles respectively) are also represented. The position of the frontal eye complex (fe), infundibular cells (io), tegmental neuropile (tg), lamellar organ (lb) and primary motor centre (pmc) are indicated. The first pigment spot of dorsal ocellus is also indicate (ps) as well as preoral organ (po), gill slits (gs) and notochord (n).