It has an extensive system of vessels making it the most complex and effective system of all the molluscs, enabling them to be much more intelligent and able to move rapidly and over extended periods of time. The two branchial hearts, which sit at the gill base, collect unoxygenated blood from all the body parts. They then contract and send this unoxygenated blood coursing throughout the capillaries of the gills. The two auricles of the heart then drain the now oxygen rich blood from the gills and pass it into the medial ventricle. The ventricle then pumps the blood out to the body via an anterior and posterior aorta, and eventually through smaller vessels and finally into tissue capillaries.
Octopuses have the most complex brain of all the invertebrates.
They have long and short-term memories. They learn to solve puzzles quite quickly. Once learned, they can rapidly solve the puzzle upon repetition and they remember how to do it in the future. They are simple open pits at the end of short stalks. They lack the complex image-forming apparatus of the other cephalopods.