Final answer:
An octopus has a closed circulatory system with three hearts: two branchial hearts for its gills and one systemic heart for its body, supporting its active predatory lifestyle and high metabolic demands.
Step-by-step explanation:
An octopus is a fascinating marine creature known for its intelligence and unique physiological attributes, one of which is its circulatory system. Unlike many other mollusks, an octopus has a closed circulatory system with three hearts. Two of these hearts are branchial or gill hearts that pump blood through each of the two gills, while the third is a systemic heart that circulates blood to the rest of the body.
The presence of multiple hearts aids in the efficient transport of oxygen in the octopus's blue blood, which is due to the copper-containing molecule hemocyanin. The adaptation of three hearts in cephalopods like the octopus is linked to their lifestyle as active predators, requiring a more efficient circulation to support their high metabolic needs. This, combined with their ability to jet-propel through water and release ink for defense, makes them exceptionally skilled in their marine environments.