Advisors: Thomas Schwaha, Andy Sombke

Master's Defensio - Wednesday, March 25th 2020

Abstract

Bryozoans are sessile aquatic suspension feeders in mainly marine, but also freshwater habitats. Most species belong to the marine and calcified Cheilostomata. Since this taxon remains mostly unstudied regarding their neuroanatomy, the focus of this study is the characterization and ground pattern reconstruction of the autozooidal nervous system of this taxon. Two classical and two modern neuronal tracing techniques were tested and evaluated for future neuroanatomical studies. The analysis is based on data from six representatives of several major cheilostome taxa. Results reveal a common innervation pattern in the investigated species. The cerebral ganglion is located at the base of the lophophore, from where neurite bundles embrace the mouth opening to form a circumoral nerve ring. Four neurite bundles project from the cerebral ganglion to innervate peripheral areas, such as the body wall and parietal muscles via the tentacle sheath. Five neurite bundles comprise the main innervation of the visceral tract. Four neurite bundles innervate each tentacle via the circumoral nerve ring. Mediofrontal tentacle neurite bundles emerge directly from the nerve ring. Two laterofrontal- and one abfrontal tentacle neurite bundles emanate from radial neurite bundles, which originate from the cerebral ganglion and circumoral nerve ring in between two adjacent tentacles. The radial neurite bundles terminate in intertentacular sites and give rise to one abfrontal neurite bundle at the oral side and two abfrontal neurite bundles at the anal side. Similar patterns are described in ctenostome bryozoans. The present result thus represents the gymnolaemate situation. Innervation of the tentacle sheath and visceral tract by fewer neurite bundles and tentacular innervation by four to six tentacle neurite bundles support cyclostomes as sister taxon to gymnolaemates. Phylactolaemates feature fewest distinct neurite bundles in visceral- and tentacle sheath innervation, which always split in nervous plexi and their tentacles have six neurite bundles. Thus, this study supports phylactolaemates as sistergroup to myolaemates.