Practice question

Cephalopods including squid, cuttlefish and octopus display closed circulatory system exception within Mollusca, adapting to active nektic predation and high oxygen consumption. System includes systemic heart with single ventricle and two atria plus two branchial hearts at base of gills augmenting pressure through gill capillaries and systemic capillaries, minimizing sinus pooling and ensuring high-pressure perfusion to large brain, muscles and chromatophores. Blood remains enclosed in vessels throughout circuit, similar to vertebrate closed design. Gastropods, bivalves and polyplacophorans retain open sinuses, highlighting cephalopod metabolic specialization correlating with jet propulsion and advanced neural development.