The Open Circulatory System of Spiders (Eurypelma californicum, Pholcus phalangioides): A Survey of Functional Morphology and Physiology

Abstract

The circulatory system of most spiders consists of the heart, pericardium, arterial vascular system, the open venous system, and lung veins connecting book lungs to the pericardium. Several important aspects of the structure and function of spider circulation have been known only in outline until now. In this study, morphological details of the heart and pericardium, which allow them to function cooperatively as a pressure-and-suction pump, are reported. The arterial vascular system and the venous open system show adaptations to cellular oxygen requirements. At least in the legs, capillarization is absent and gas exchange with the tissues has to take place primarily along the open portion of the circulatory system. Cardiac output increases through higher stroke volumes and/or heart frequencies. Possible mechanisms for changes in the hemolymph flow distribution are discussed. The animal's body pressures, generated byprosomal and opisthosomal muscles, strongly interfere with normal circulation during locomotor activity.