Fig. 2

Serotonergic nervous system of P. californiensis larvae. Larval anterior is up on all panels. a Confocal z-projection of anti-serotonin antibody labeling in invagination-stage larva. Larva possesses seven serotonergic neurons, two of which appear to innervate the anterior invaginations. Neuron labels: ap apical neuron, san subapical neuron, aan additional apical neuron, cn caudal neuron. Asterisk indicates apical organ. aʹ Overlayed fluorescent and transmitted-light image. b Confocal z-projection of anti-serotonin antibody labeling of the early-rudiment-stage larva. b′ Overlayed fluorescent and transmitted-light image. c Confocal z-projection of anti-serotonin antibody labeling of late-rudiment-stage larva. c′ Overlaid fluorescent and transmitted-light image. Scale bars 15 µm.