The nervous and muscular systems in the free-living flatworm Castrella truncata (Rhabdocoela): an immunocytochemical and phalloidin fluorescence study

In order to broaden the information about the organisation of the nervous system in the Plathelminthes, an immunocytochemical (ICC) study of the free-living flatworm Castrella truncata (Dalyellioida) has been performed. This is the first time a representative of the taxon Rhabdocoela has been studied with the ICC technique. Antibodies to 5-HT and FMRF-amide and confocal scanning laser microscope were used. 5-HT and FMRF-amide immunoreactivity was observed in the neuropile of the brain, in the cerebral neurones, in the three pairs of longitudinal nerve cords and the adjoining neurones, in the pharyngeal nerve ring and in twelve neurones associated with the pharynx. 5-HT and FMRF-amide immunoreactivity occurs in separate sets of neurones. Only FMRF-amide immunoreactivity was observed in a peculiar ellipse-shaped structure in the brain, and in the genital plexus. The type of orthogon is discussed. Staining of the muscular system with TRITC conjugated phalloidin revealed muscle patterns that have not been described previously.