Octopuses Have Three Hearts and Blue Blood
Octopuses have three hearts and blue blood due to copper-based hemocyanin instead of iron-based hemoglobin, and two hearts stop beating when they swim.
About this fact
Octopuses possess one of the most unusual circulatory systems in the animal kingdom. They have three hearts: two branchial hearts that pump blood through their gills, and one systemic heart that pumps blood through the rest of their body. Their blood is blue because it contains hemocyanin, a copper-based protein that transports oxygen more efficiently than iron-based hemoglobin in cold, low-oxygen environments. Remarkably, when an octopus swims, its systemic heart stops beating, which is why they prefer crawling along the seafloor - swimming exhausts them quickly. This unique physiology helps explain why octopuses are such efficient deep-sea predators.