Comparative morphology of the hemolymph vascular system in mygalomorphs (Araneae: Opisthothelae)

Mygalomorphs are a well-known spider group; however, astonishingly little is known about their internal anatomy. As part of a comparative survey on the circulatory system in spiders, we conducted an examination of the hemolymph vascular system (HVS) and parts of the hemolymph lacunar system (HLS) in five mygalomorph spider species. Circulatory system features were investigated using micro-computer-tomography in combination with resin injection methods and serial sectioning. Data were visualized using a 3D-reconstruction software. The HVS consists of a tubular heart, which is situated along the dorsal midline of the opisthosoma. Anteriorly, the heart gives rise to the anterior aorta. A posterior aorta system was not found. Three pairs of cardiac arteries originate laterally from the heart and the branching pattern of these arteries is visualized and described here for the first time. The anterior aorta runs through the pedicel into the prosoma where it branches to supply the muscles and particularly the central nervous system. The data on mygalomorphs are discussed in comparison to the HVS in other Araneae.