How many hearts does an octopus have?

An octopus has three hearts! Two of these hearts are called 'branchial hearts' since they are responsible for circulating blood over the octopus's gills, while the third heart is the 'systemic heart' that circulates blood throughout the body.

Unlike most animals with a single heart, the three hearts of an octopus work together to help the octopus survive in its aquatic environment. The branchial hearts move the blue blood (low in oxygen) through the octopus's gills where it is enriched with oxygen, while the systemic heart pumps the oxygen-rich blood throughout the octopus's body.

It's important to note that the blood of an octopus actually carries a copper-rich protein called hemocyanin instead of the iron-rich hemoglobin found in human blood. This gives their blood a blue color and makes it particularly suited for carrying oxygen in cold ocean waters.