The hemolymph vascular system in Araneus diadematuswith special focus on intraspecific variability in artery systems

Abstract

The European garden spider, Araneus diadematus Clerck, 1757, is one of the most common spiders in central Europe. However, despite its abundance, comparatively little is known about its internal anatomy. We therefore conducted an examination of the hemolymph vascular system (HVS) of A. diadematus, as part of a comparative survey on the circulatory system in spiders. The HVS of A. diadematus was investigated using micro-computed-tomography and serial sectioning and visualized using 3D-reconstruction software. In order to examine the HVS for intraspecific variability, over 30 specimens were studied in detail. The HVS of A. diadematus consists of a tubular heart, which is situated along the dorsal midline of the opisthosoma. Anteriorly, the heart gives rise to the anterior aorta and posteriorly to the posterior aorta. Three pairs of cardiac arteries originate from the dorso-lateral section of the heart and the branching pattern of these arteries in A. diadematus 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 organs with hemolymph. The central nervous system in particular is supplied by a large number of arteries, which show some interesting branching patterns, e.g., a unilateral origin of the transganglionic arteries in the subesophageal ganglion, and the supply of the lower lip by the first of these transganglionic arteries. Furthermore, there are a number of arteries in the HVS with unilateral (asymmetrical) origins. Some cases of intraspecific variability are demonstrated, e.g., for the arteries of the upper and the lower lip. The data presented here are discussed in reference to information on the HVS in Araneae available in existing literature.