THE OPEN CIRCULATORY-SYSTEM OF SPIDERS (EURYPELMA-CALIFORNICUM, PHOLCUS-PHALANGIOIDES) - A SURVEY OF FUNCTIONAL-MORPHOLOGY AND PHYSIOLOGY

The circulatory system of most spiders consists of the heart pericardi um, arterial vascular system, the open venous system, and lung veins c onnecting 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 hear t and pericardium, which allow them to function cooperatively as a pre ssure-and-suction pump, are reported. The arterial vascular system and the venous open system shout adaptations to cellular oxygen requireme nts. 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 strok e volumes and/or heart frequencies. Possible mechanisms for changes in the hemolymph flow distribution are discussed. The animal's body pres sures, generated by prosomal and opisthosomal muscles, strongly interf ere with normal circulation during locomotor activity.