Comparative immunohistochemical investigation on the nervous system of two species of Arthrotardigrada (Heterotardigrada, Tardigrada)

The question whether tardigrades possess a tripartite, segmented brain and a subpharyngeal ganglion or not is a matter of ongoing debate. This study sets out to analyze the structure of the nervous system of Batillipes pennaki and Actinarctus doryphorus ocellatus in order to provide new insights specially into the organization of the tardigrade brain. Based on the assumption that tardigrades are members of the taxon Panarthropoda rather than of the taxon Cycloneuralia, insights into the organization of their brain could help to clarify their relationship within Panarthropoda. Our results indicate that B. pennaki and A. doryphorus ocellatus neither possess a tripartite brain nor a subpharyngeal ganglion. The implications of these findings are discussed and compared with reference to previous studies.