Here are seven such animals that have captured the curiosity of scientists and nature enthusiasts alike.
Octopus have 3 hearts. Two of these hearts pump blood to the gills, while the third heart circulates oxygen-rich blood throughout the body.
Earthworms may seem simple, but they have a complex circulatory system. They have five pairs of aortic arches which function as hearts.
Hagfish are primitive marine creatures that have four hearts. These hearts work together to pump blood throughout their bodies.
Squids also have three hearts. Two of these hearts are responsible for pumping blood to the gills, while the third heart circulates blood to the body.
Cockroaches also possess a unique circulatory system. They have a tubular heart that runs along their back and helps pump blood into their open circulatory system.
Cuttlefish have three hearts, with two hearts dedicated to pumping blood to the gills, and the third heart circulating blood throughout their body.
Blue-ringed octopus: This small but venomous octopus boasts three hearts.