The adult serotonergic nervous system of Hislopia malayensis. Maximum-intensity projections of confocal laserscanning image stacks. (a) Lateral view of the lophophoral base showing the cerebral ganglion at the proximal side and parts of the circumpharyngeal neurite bundles emanating to serotonergic perikarya at the lophophoral base. From the latter, two neurites are distinguishable at the base of each adjacent tentacle. (b) Oral view of the serotonergic nervous system at the lophophoral base. The highest concentration of serotonin is found in the cerebral ganglion on the left side. At the oral side, three serotonergic perikarya are present associated with the circumpharyngeal neurite bundle. Further neurites extend towards the serotonergic perikarya from the ganglion and the circumpharyngeal ring. Abbreviations: cg - cerebral ganglion, cpn - circumpharyngeal neurites, bp - perikarya at the lophophore base, obp - perikarya on the oral side of the lophophoral base, nt - neurites extending into the tentacles.