Fig. 8

5-HT-like immunoreactivity (5-HT-lir) in the early and late rudiment stage larvae of Quasitetrastemma stimpsoni. Red - 5-HT-lir; green–cilia, acetylated tubulin immunoreactivity; blue—nuclei, DAPI. The apical pole is always upward; side view. a General view of 5-HT-lir in early rudiment stage larva, 48 h post-fertilization (hpf), with apical neurons (an) and paired lateral neurons (ln) located along the lateral nerve cord (lnc). a1-a2 High-magnification inset shows apical plate cells innervated by neurites (arrows) of apical neurons. a3-a5 High-magnification inset shows the apical neurons (asterisks) localized near dorsal commissural tract (dc). b General view of 5-HT-lir in late rudiment stage larva (70 hpf). b1-b2 5-HT-lir cells (asterisks) in the apical plate are innervated by neurites of apical neurons (arrows) and form a single axon (black arrowhead) projecting onto the subepithelial nerve plexus. Localized under the apical plate is a pair of 5-HT-lir subapical neurons (white arrowhead). b3-b5 High-magnification inset of apical neurons (asterisks) localized near dorsal commissural tract (dc). Abbreviations: an–apical neuron; dc–dorsal commissural tract; ln–lateral neuron; lnc–lateral nerve cord