Like humans, most animals have a single heart. However, some animals do not have hearts at all like the starfish and some echinoderms while other animals like cephalopods have several hearts. Animals like octopuses and squids have up to three hearts; one heart that pumps blood to all the parts of the body and two other hearts that pump blood through the gills where it mixes with oxygen. Interestingly, some animals have up to five hearts. Even though these animals have more than one heart, only one of the many hearts functions as the primary heart. The rest of the hearts only supplement the main heart. Here are some of the animals with more than one heart.
Earthworms have five pairs of heart-like structures known as arches. While the aortic arches are not technically hearts, they perform a similar function as the heart and are typically referred to as heart. The aortic arches are segmented and run along the length of the worm’s body. Unlike human hearts which have multiple chambers, aortic arches have only one chamber. One of the five hearts acts as the primary heart that pumps blood to the rest of the segments. Worms regulate heartbeat using their nerve cells.
A cockroach has one heart divided into 13 chambers and is more resistant to failure compared to the human heart. The chambers are shaped like tubes and organized sequentially with each chamber pushing blood into the next until the last chambers reach an ideal output pressure. The last chamber of the heart pumps oxygenated blood to the other parts of the body and other organs. Thus, if one chamber fails, the heat can still function, but with less efficiency. The dorsal sinus on top of the cockroach assists in sending oxygenated blood to the various chambers of the heart.
The octopus has three hearts in total with one of the hearts functioning as the systematic heart that pumps oxygenated blood to the other body parts. Two of the three hearts are referred to as brachial hearts and pump blood through the gills for oxygenation. Unlike most vertebrates with iron-rich hemoglobin packed in their blood, octopuses have copper-rich hemocyanin that dissolves directly into their blood making their blood to appear blue. Hemoglobin is more efficient than hemocyanin as an oxygen transporter. Thus, the three hearts compensate by pumping blood around the body at a faster rate to supply the needed oxygen for the octopus’ active lifestyle.
Like an octopus, the squid has three hearts; one systematic heart and two branchial hearts. The two hearts pushes the blood through the gills where it mixes with oxygen. From the gills, the blood flows into the systematic heart where it pumped to other body parts. The systematic heart is subdivided into three chambers; two upper auricles and a lower ventricle.
Hagfish have primitive circulatory systems composing of four hearts and 5-15 pairs of gills. The main heart, known as branchial heart, pumps the blood to all parts of the body while the other three hearts serve as accessory pumps. Hagfish are sometimes referred to as slime eels due to their eel-shaped bodies.