Figure 1

Development of ciliary structures and serotonergic system in H. trivolvis. Anti-α-tubulin (magenta) and anti-5-HT (green) immunostainings were imaged in a laser confocal microscope. In A and D-G, confocal images were combined with transmission light images. (A-C) Early trochophore (stage 19). (A) Two apical neurons (arrows), dorsolateral (dl) and pedal (p) ciliary bands are present. (B) Higher magnification of the apical neuron with dendritic knob, which bears short cilia (arrow), thin back branches (arrowheads), and primary neurite (open arrow). (C) Primary neurite (open arrow) with numerous thin branches underneath the pedal band of cilia (p). (D) Middle veliger in the beginning of metamorphosis (stage 23). Dorsolateral and pedal ciliary bands are complemented by foot ciliary fields (fc), tentacle ciliary fields (tc) and numerous body wall ciliary brushes (br). Two apical 5-HT neurons (arrows) and 5-HT positive cells within cerebral and pedal ganglia (open arrows) are present. (E) veliconcha in the middle of metamorphosis (stage 25). Dorsolateral ciliary bands are not visible, whereas all other ciliary structures are present. Insert, high magnification of the apical 5-HT neuron with ciliated dendritic knob. (F, G) H. trivolvis at the end of metamorphosis (stage 27), anterior (F) and dorsal (G) view. Serotonin-immunostaining is present in neurons of central ganglia (open arrows) and their peripheral processes only. Foot and tentacle ciliary fields (fc, tc) and numerous body wall ciliary brushes (br) are present. Note that 5-HT-immunopositive apical neurons, cilia on their dendritic knobs as well as dorsolateral and pedal ciliary bands are not visible. ll – lung lobe, m – mouth, e – eye, r – radular sack.