Fig. 6

Mutual distribution of FMRFamide-lir, 5-HT-lir and acetylated α-tubulin in the stages of the larvae of Azumapecten farreri. Green: 5-HT-lir, magenta: FMRFamide-lir, blue (a–d, a1–d1 or white (a2–d2)): acetylated α-tubulin-lir. a FMRFamide-lir and 5-HT-lir components of the larval nervous system in the 48-hpf early veliger stage with apical organ (AO), dorsal neuron (dn) and neurites extending to the ventral part of the larvae. Inserts: a1 Two paired 5-HT-lir cells (asterisks) lie between two FMRFamide-lir cells (asterisk) of the apical organ (AO) near the apical tuft of cilia (at). In the central part of the AO, neurites form the neuropil. b The larva of the middle veliger stage is 72 hpf. AO includes 5-HT-lir cells (asterisk) and FMRFamidel-lir cells (asterisk). From FMRFamide-lir cells extending to the ventral side of the larva, there appear pleural neurons (pln) and down ventral neurons (vn). the dorsal part of the larva lie dorsal neurons (dn). The nerve cord extends from AO to the ventral side of the larvae—visceral nerve cord (vnc). Inserts: b1 The AO including 5-HT-lir cells (asterisk) and FMRFamide-lir cells (asterisk). c Larva at the veliger stage (7 dpf) demonstrate the presence of FMRFamide-lir elements in the CG (transformed from AO) including 5-HT-lir cells and FMRFamide-lir cells, visceral ganglion (VG) include only FMRFamide-lir elements, pleural ganglion (PlG) include only FMRFamide-lir elements, FMRFamide-lir dorsal neurons (dn) and interstitial innervation (ems). Inserts: c1 Transformed CG extending from four paired visceral cords (two 5-HT-lir cords and two FMRFamide-lir cords). d The 25-dpf pediveliger stage with the CG (including 5-HT-lir cells and FMRFamide-lir cells), four paired visceral cords (two 5-HT-lir cords and two FMRFamide-lir cords) (vnc), pedal ganglion (PG) including only FMRFamide-lir elements, and visceral ganglion (VG) including only FMRFamide-lir elements located along the visceral cords (vnc). Inserts: d1 Cerebral ganglion CG and visceral cord. From CG to the dorsal part of the larvae extends 5-HT-lir neurites and FMRFamide-lir neurites. Additional abbreviations: a—anus, m—mouth, st—stomach v—velum. The orientation a—anterior, d—dorsal, p—posterior, v—ventral. Scale bars = 20 μm