How Many Hearts Does an Earthworm Have?

Earthworms don't have "hearts," but do have aortic arches that help them digest soil.

An earthworm does not have any heart at all. But they do have an organ that acts similar to a heart and is usually called a heart just for simplicity's sake, although it is also called an aortic arch. Earthworms have five of these arches. In between each arch is a gland that helps the worm digest calcium, which it gets from eating a lot of dirt.

Size

The heart and calciferous gland section makes up less than five percent of an earthworm's total body length, no matter how big the individual worm gets.

Function

The aortic arches (hearts) help pump blood around the body of the earthworm in a similar way to animals that have only one multi-chambered heart. Worm "hearts" don't have chambers. Worms also don't have lungs. They absorb oxygen through their skin and then it gets into their blood vessels. The dorsal blood vessel does a bit of the pumping work, with the hearts helping to keep blood pressure steady.

Identification

Earthworm hearts and the glands in between them are found just behind the brain (called a ganglion) and wrapped around the esophagus. Right in front of the brain is the mouth. The calciforous glands and arches are needed near to where the food enters in order to efficiently get the energy the body needs on its way.

Misconceptions

Part of an earthworm's body will grow into an entirely new worm if it is cut off from the original worm. Just where and how much of the worm can be cut off to grow another worm depends on which of the 2,700 species of earthworm it happens to be. However, if you cut out the aortic arches, you'll just have a very dead worm.

Significance

An earthworm has what scientists consider a primitive form of a heart. However, the earthworm has been around for at least 500 million years--a lot longer than many mammal species, so perhaps this "heart" is quite ahead of it's time.

Types

All of the aortic arches in the earthworm perform the same function, so there aren't any different types of earthworm hearts. But an earthworm needs five in order to help get the blood to go all through it's long body, which can range anywhere from a few millimeters to 22 feet long.

Resources

• Backyard Nature: Earthworms