Practice question

Most molluscs possess open circulatory system where heart located in pericardial cavity pumps hemolymph through short aorta into large blood sinuses bathing tissues directly within hemocoel, then collecting via venous sinuses returning to ctenidia for oxygenation and to heart via atria. System operates low pressure, relatively slow flow sufficient for sluggish benthic molluscs. Cephalopods diverge with closed circulation confining blood to vessels with capillary beds. Closed, absent or lacunar descriptors inaccurate for majority. Open design reflects reduced coelom and metabolic demands, forming functional analogy with arthropod hemocoel circulation.