Z-stack compressions showing triple labelling of different cell types in the gills of bowfin with serotonin antibody (5-HT, green) and the neuronal marker antibody (zn-12, magenta), and the cell nuclei with DAPI (blue). Z-stack compressions showing triple labelling of different cell types in the gills of bowfin with serotonin antibody (5-HT, green) and the neuronal marker antibody (zn-12, magenta), and the cell nuclei with DAPI (blue). (A) Type I cells are found in close proximity to nerve fibres. (B) Type II cells contain synaptic vesicles confirming that they are bipolar neurons. (C) Type III cells were found in close proximity to nerve fibres. (D,E) Type IV (D) and V (E) cells were never located near nerve fibres, therefore were not innervated. Scale bars: 10 μm. Cosima S. Porteus et al. J Exp Biol 2014;217:1269-1277 © 2014. Published by The Company of Biologists Ltd