Lacking in nautiloids. Blue, yellow, orange, red, black pigments in these cells which overlie reflective cells called iridocytes. Also used in courtship. This is used to startle prey, lure prey, attract mates and as countershading for camouflage at intermediate water depths. Increased folding of gill surface increases area for absorption.
Branchial heart increases blood pressure pushing blood through each gill.
Other species filter ions from the coelomic fluid into the renal sac. All dumps into the mantle cavity through a nephridiopore. V. Nervous System, Sense Organs and Behavior Greatest cephalization among inverts. Memory and learning well demonstrated. Lots of work on learning in squid and octopus.