Octopuses Have Three Hearts — And Blue Blood

You probably already know that octopuses are remarkable creatures. They can change color in less than a second, squeeze through tiny gaps, and open jars with their arms. But here is something that may surprise you: an octopus has not one, not two, but three hearts.

Two of an octopus's hearts — called branchial hearts — are located near each gill. Their job is to pump blood through the gills, where it picks up oxygen. The third heart, called the systemic heart, then takes that oxygenated blood and pumps it to the rest of the body.

There is a curious side effect to this system. When an octopus swims, the systemic heart temporarily stops beating. This is why octopuses tire so quickly when swimming and prefer to crawl along the seafloor instead.

Octopus blood is not red — it is blue. Human blood gets its red color from hemoglobin, a protein that contains iron. Iron binds to oxygen and carries it through the body. Octopuses use a different protein called hemocyanin, which contains copper instead of iron. Copper gives hemocyanin its distinctive blue color.

Hemocyanin is less efficient at carrying oxygen than hemoglobin, which is one reason octopuses tire easily. However, it has one advantage: it works better in cold, low-oxygen environments — ideal for life on the ocean floor.

Three hearts and blue blood are just two of the many unusual features of the octopus. Their intelligence is also distributed: roughly two-thirds of an octopus's neurons are located in its arms rather than its central brain. Each arm can process sensory information and react to its environment somewhat independently, without waiting for instructions from the brain.

The octopus is a reminder that evolution can find radically different solutions to the same problems. Where humans evolved one heart and red blood, the octopus evolved three hearts and blue blood — and both work remarkably well in their own environments.