The morphology of the nervous system of Wirenia argentea (Solenogastres) is described based on histological and immunocytochemical analyses using fluorescent markers against the neurotransmitters serotonin and FMRFamide, as well as acetylated -tubulin, in combination with confocal laser-scanning microscopy. The nervous system displays a distinct tetraneury with fused cerebral ganglia, large pedal ganglia, and longitudinal nerve cords connected by regularly spaced connectives and commissures resulting in an orthogon-like arrangement. There is no indication of metamery. FMRFamidergic immunoreactivity is present in most compartments of the nervous system, while serotonergic immunoreactivity appears to be restricted to the longitudinal nerve cords, the cerebro-pedal commissure and part of the cerebral ganglion. The buccal system shows immunoreactivity against none of the neurotransmitters.