Octopuses Have Three Hearts

An octopus's trio of hearts is a fascinating solution to the challenges of its deep-sea environment and unique biology. Unlike vertebrates with their iron-rich, red blood, octopuses have blue blood that utilizes a copper-based protein called hemocyanin to transport oxygen. This adaptation is advantageous in cold, low-oxygen water as hemocyanin is more efficient than hemoglobin under these conditions. However, hemocyanin is less efficient at carrying oxygen overall, making the octopus's blood thicker and requiring more pressure to circulate throughout its body. This is where the three hearts come into play, compensating for the less efficient oxygen transport of their blue blood.

The division of labor among the three hearts is a marvel of efficiency. Two branchial hearts are dedicated to pumping blood through the gills to be oxygenated. The third, more powerful systemic heart is then responsible for circulating this oxygen-rich blood to the rest of the body, supplying the necessary energy for their active and predatory lifestyle. This complex circulatory system supports the octopus's large brain and distributed nervous system, with a significant portion of its neurons located in its arms.

Interestingly, the systemic heart of an octopus stops beating when it swims. This physiological quirk makes swimming an exhausting activity for these intelligent invertebrates. As a result, they often prefer to crawl along the ocean floor, a more energy-efficient mode of transportation that allows their systemic heart to continue its vital work. This preference for crawling is a direct consequence of their unique three-hearted circulatory system and the composition of their blood.