Fig. 4

Neuropeptide-lir elements in the competent larvae. CLSM images of DAPI (cyan), acetylated tubulin (yellow) and neuropeptide-lir (red or white) elements in the competent larvae (~ 3 wpf). Apical views, with anterior to the top. c–f, i–l, o–p and s–v are close ups of the foregut or apical organ in the same view as the respective larger image in b, h, n, r. a–b, e–f FVamide-lir cells and q–r, u–v MIP-lir cells in the apical organ connect via FVamide-lir and MIP circumesophageal connectives (cc) to the ventral nerve cord (vnc) of the juvenile trunk rudiment (jr) (See Additional file 3: Supplementary Fig. 3), and via a–b FVamide-lir, g–h RYamide-lir and q–r MIP-lir frontal (fn), dorsal (dn) and peripheral nerves (orange arrow heads) to the a–b FVamide-lir, g–h RYamide-lir and q–r MIP-lir prototrochal ring (pr). An e–f FVamide-lir, i–j RYamide-lir and u–v MIP-lir apical nerve ring (ar) surrounds the apical tuft. The foregut is innervated by a–d FVamide-lir cells and neurites. k–l RYamide-lir axons form a neuropil between two brain lobes (rbl–lbl) underneath the apical organ. m–p RGWamide-lir cells remain only in the apical organ. Arrow in r, t is presumably background staining.an: anus; ao: apical organ; ar: apical nerve ring; at: apical tuft; br: brain; cc: circumesophageal connectives; chn: chaetal sac nerve; cs: chaetal sac; dn: dorsal nerve; dr: dorsal root; fg: foregut; fgn: foregut nerve; fn: frontal nerve; jr: juvenile rudiment; mg: midgut; mo: mouth; np: brain neuropil; pr: prototrochal ring; pt: prototroch; vr: ventral root