Which animals have more than one heart?
Humans have one heart. Most animals have one heart, but there are animals with no heart, such as the jellyfish, and there are animals with more than one heart.
The heart transports, or circulates, oxygen in the blood around the body. This is called the circulatory system. The human heart has red blood cells called haemoglobin. The human heart has 4 chambers (two atria and two ventricles). The cockroach, for example, has one heart with 13 chambers. The earthworm has 5 pseudo-hearts (false hearts) that are really aortic arches that act similar to a heart.
The animals that have more than one heart include the Octopus, Squid, Cuttlefish, and Hagfish.
The Octopus, in the Octopodidae family and Cephalopoda class of marine (saltwater) molluscs, has 3 hearts.
The Octopus has one main heart that circulates blood around the body and two branchial hearts that pump blood through its two gills (that help it to breathe) to the main heart. The branchial hearts are also known as gill hearts.
Each heart has 3 chambers (two atria and one ventricle). Its blood does not have red blood cells. Instead of haemoglobin, the blood of an Octopus has haemocyanin, and so it appears blue. Its blood is very thick and it is extremely difficult to pump the blood around the body. That’s why it needs two branchial hearts to help the main heart. The main heart is not active when the Octopus is swimming, which is why it does not swim for long distances. It is benthic, which means that it is a bottom-dweller and prefers to crawl on the bottom of the sea.
The Octopus lives for 2-15 years, on average. Human beings live for 64-69 years, on average, depending on the country where they live, and many other factors. So, having three hearts does not make the Octopus live three times longer than a human!
The Squid, also in the Cephalopoda class of marine (saltwater) molluscs, has 3 hearts. Like the Octopus, the Squid has thick, blue blood which is difficult to pump around its body. The Squid lives for 3-5 years on average.
The Cuttlefish is also a Cephalopoda class of marine (saltwater) molluscs. It also has 3 hearts with blue blood like the Octopus and the Squid. The Cuttlefish lives for 1-2 years on average.
The Hagfish is different from the cephalopods. It is in the Myxini class and Myxinidae family of marine (saltwater) animals that looks like an eel, but it is not a true eel. The Hagfish has 4 hearts. Instead of two gills (like the Octopus, Squid, and Cuttlefish), it has between 5-15 pairs of gills. Its branchial heart pumps blood to the body, and its three other hearts (auxiliary hearts) pump blood through its many gills to the branchial heart or other hearts.
The branchial heart has 2 chambers (one atrium and one ventricle). The auxiliary hearts are the 1) caudal heart, 2) portal heart, and 3) cardinal heart.
Unlike the cephalopods, the hearts of the Hagfish can continue beating without oxygen for up to 36 hours. The Hagfish also has twice as much blood in its body than other fish. The blood contains haemoglobin, so it is reddish.
The Hagfish is benthic, living on the bottom of the ocean. It is sluggish and slow moving. It is estimated that the Hagfish lives for about 40 years on average.
Therefore, the animals that have more than one heart live in the sea, and specifically, they are benthic, living on the bottom of the sea. Most of the species are cephalopods, which include the Octopus, Squid, and Cuttlefish.
Location of photographs: Aquarium de Paris-Cinéaqua, France, and the Pacific Hagfish (Eptatretus stoutii) by Linda Snook (2009), National Oceanic and Atmospheric Administration (NOAA)
Photographer: Martina Nicolls
Martina Nicolls: SIMILAR BUT DIFFERENT IN THE ANIMAL KINGDOM