The nervous system of Neodasys chaetonotoideus (Gastrotricha: Neodasys) revealed by combining confocal laserscanning and transmission electron microscopy: evolutionary comparison of neuroanatomy within the Gastrotricha and basal Protostomia

We present a reconstruction of the nervous system of Neodasys chaetonotoideus Remane, 1927 (Gastrotricha, Chaetonotida) based on different microscopical methods: (1) immunohistochemistry (anti-acetylated α- and β-tubulin-, anti-5-HT- and anti-FMRFamide labelling) and (2) histochemistry (labelling of musculature and nuclei) by the means of confocal laser scanning microscopy (cLSM) and (iii) ultrastructure by means of transmission electron microscopy (TEM). All parts of the nervous system contain structures with an immunoreaction against the used immunohistochemical markers and labelling of histochemical markers. Results of both techniques (cLSM, TEM) reveal that the nervous system of N. chaetonotoideus is composed of a “dumb-bell-shaped” brain and one pair of posterior longitudinal neurite bundles. The brain is made up of a pair of laterally located clusters of neuronal somata, a large dorsal interconnecting dorsal commissure and two tiny ventral commissures in the region of the lateral clusters. From this, it follows that the brain is circumpharyngeal in position. The innervation of the head region is conducted by three pairs of anterior-directed neurite bundles. We describe here the gross anatomy of the nervous system and give additional details of the ultrastructure and the 5-HT and RFamide-like IR components of the nervous system. We compare our newly obtained data with already published data on the nervous system of gastrotrichs to reconstruct the hypothetical ground pattern of the nervous system in Gastrotricha, respectively, in Macrodasyida.