Architecture of the Central Nervous System in Nemathelminthes
Zusammenfassung der Projektergebnisse
It was the aim of the study to provide and compare detailed information on the nervous system of representatives from the taxa Gastrotricha, Nematomorpha, Kinorhyncha, Priapulida and Loricifera (traditionally members of the "Nemathelminthes" based on immunohistological staining techniques and confocal laser scanning microscopy. All these taxa have a cuticle, which, at least in those representatives that have a thick cuticle, poses methodological problems for the penetration of antibodies. Staining of the nervous system with different antibodies was very successful in the taxon Gastrotricha, where >25 species spanning the entire gastrotrich diversity could be investigated. The nervous system shows a conservative basic structure and is composed of a commissural brain dorsal of the pharynx with lateral clusters of the somata of brain nerve cells. Paired longitudinal nerve cords originate from the lateral parts of the brain and run in a lateroventral position in the posterior direction. Fine differences are present in the patterns of neurites running into the head region, the number of fine commissures between the longitudinal nerve cords and in the presence or absence of a posterior nerve cell along the cord. Kinorhynchs and priapulids have a so-called cycloneural brain, which is composed of a circumpharyngeal ring neuropil with anteriorly and posteriorly located somata. From the ventral region of the ring an unpaired (Priapulida) or paired (Kinorhyncha) nerve cord originates. In the priapulid "Tubiluchus troglodytes" an orthogonal pattern of fine longitudinal and perpendicular (ring-like) neurites is present. Staining in nematomorphs was unsuccessful and sampling of loriciferans was unsuccessful, therefore these taxa have to be excluded. Our investigations confirm older reconstructions of the gastrotrich nervous system, while two younger reconstructions based on transmission electron microscopy could not be confirmed. Additionally it is confirmed that Priapulida and Kinorhyncha have a cycloneural nervous system, as has been stated as an autapomorphy of Cycloneuralia (Nematoda, Nematomorpha, Kinorhyncha, Priapulida, Loricifera). An orthogon has been demonstrated for the first time in Priapulida. The evolutionary transitions towards a cycloneural brain remain difficult to explain and the nervous system does not provide useful characters to unite Gastrotricha and Cycloneuralia within a taxon Nemathelminthes. The data gained in this project are integrated in a larger cooperation with other groups in the Deep Metazoan Phylogeny project. A glossary on neuroanatomical terms has been published and we are currently working on a phylogenetic analysis of a data matrix assembled with data from the DMP projects and additional literature data.
