Octopuses have three hearts and blue blood

Octopuses are remarkable marine creatures with unique cardiovascular adaptations. Unlike humans with iron-based hemoglobin (red), octopuses use copper-based hemocyanin, giving blood a distinctive blue color. Hemocyanin is more efficient at transporting oxygen in cold, low-oxygen ocean environments. Two smaller hearts circulate blood through the gills, while a larger heart pumps oxygenated blood throughout the body. When an octopus swims, the heart delivering blood to the body stops beating, which is why these creatures prefer crawling to conserve energy. This cardiovascular design represents an evolutionary solution to deep-sea living challenges.