The nervous system of Tricladida. IV. Neuroanatomy of Planaria torva (Paludicola, Planaridae): an immunocytochemical study

Characters of the nervous system have scarcely been used in consideration o f the phylogenetic relationships of the Tricladida. In order to contribute characters toward this end, we studied the nervous system of Planaria torva with immunocytochemical methods and we compare the results with what is kn own of nervous system structure in other triclads. Antisera against four ne uroactive substances were used: neuropeptide F (NPF), RFamide, GYIRFamide, and serotonin (5-HT). All four substances showed positive immunoreactions t hroughout the nervous system; and the patterns of distribution of the first three were similar, while 5-HT showed a distinct distribution. The organiz ation of these nervous system elements in Planariidae and Dendrocoelidae re sembles that of the Maricola but differs from that of the Dugesiidae. The r esults support the hypotheses that the Paludicola is a more advanced taxon than the Maricola and that the Planariidae and Dendrocoelidae together are a sister group of the Dugesiidae.