An Octopus Has Three Hearts and Blue Blood

Two hearts pump blood to the gills, and one pumps it to the rest of the body—but it stops beating when the octopus swims.

Octopuses are among nature’s most fascinating creatures. They have three hearts—two to move blood through their gills and one for the rest of their body. Oddly enough, that main heart stops beating when they swim.

Their blood is also blue, not red, because it uses copper (hemocyanin) instead of iron to transport oxygen—an adaptation for life in cold, low-oxygen environments.