Practice question

Open circulatory system characterized by heart pumping hemolymph through short open-ended arteries into large interconnected sinuses forming hemocoel where hemolymph directly bathes tissues without continuous endothelial separation, mixing blood and interstitial fluid, returning to dorsal heart via ostia equipped with valves. Hemolymph pressure low, but metabolic demands met in many arthropods and most molluscs partly because tracheal system supplies oxygen or small size. Annelids, earthworms, cephalopods and chordates possess closed circulation confining blood within vessels enabling higher pressure and directed flow.