Primary study on neuronal development of the embryo and early larvae of the mussel Mytilus coruscus

In the present study,the development of FMRFamide-,serotonin-containing cells in the mussel Mytilus coruscus was examined using immunocytochemical and histofluorescent techniques.During the embryonic development,no FMRFamide-like immunoreactive(lir)and serotonin-lirsensory cell appeared.Neurogenesis started during the trochophore stage at the apical extreme with the appearance of one FMRFamide-lircell and one serotonin-lir sensory cell.The numbers of FMRFamide-lir cell increased at 36 hours postfertilization(hpf)and appeared on the two sides of apical extreme.Fibres of two lateral FMRFamide-lir apical cells projected posteriorly and reached developing foot.The location of the first FMRFamide-lir apical cells in the most ventral apical region did not change during early development.At 48 hpf,three FMRFamide-lir apical cells,two lateral FMRFamide-lir apical cells and two cells of developing foot appeared.The FMRFamide-lirfibres projected and the basal neuropil formed.The earliest serotonin-lir cell appeared at 18 hpf at the anterior extreme of the apical region of developing apical organ.At 30 hpf and 36 hpf,the serotonin-lir cell extended a short basal fibre into the region of the developing neuropil of the apical organ.The numbers of the serotonin-lir cell increased to 2-3 at 42 hpf and appeared in the apical region of the D-shaped larvae.Four serotonin-lir cells were detected at 48 hpf and these cells projected basal fibres into the compact apical neuropil.