Octopuses have three hearts. Two of these hearts pump blood to the gills, where oxygen is picked up, and the third heart pumps oxygenated blood to the rest of the body.
Like octopuses, squids also possess three hearts. Two hearts pump blood to the gills, and one heart pumps oxygenated blood to the body.
Cuttlefish, closely related to octopuses and squids, also have three hearts with a similar function.
Earthworms have multiple segments along their bodies, and each segment contains a pair of aortic arches, which function as tiny hearts. These hearts help pump blood throughout the worm's body.
Hagfish are primitive marine animals that possess four hearts. Two of the hearts pump blood to the gills, while the other two pump oxygenated blood to the rest of the body.