Practice question

Circulatory design in arthropods is typically open, where dorsal heart pumps hemolymph through short arteries that open into large sinuses collectively termed hemocoel bathing tissues directly. Hemolymph returns via ostia within heart wall. Blood pressure relatively low, flow sluggish except in cephalopods with closed system and annelids with segmental vessels and capillaries. Open system reduces vascular complexity, accommodates molting where hemolymph pressure aids ecdysis, but limits capacity for sustained high metabolism compensated by tracheal oxygen delivery in insects. Double circulation refers to pulmonary and systemic loops of vertebrates, absent in arthropods.