The earthworm’s body is well adapted1 for life in the soil. Click on the labels to see images and learn more.
Click the green button to see what’s on the outside of an earthworm.
Transcript
Pharynx
Earthworms push the pharynx out of their mouths to grasp hold of organic matter2. They pull the food back into their mouths and then wet it with saliva3.
Acknowledgement: Sara L Roggemann, Three Flowers Photography
Gizzard
Earthworms do not have teeth, so they use the strong muscles of the gizzard (and grains of sand and soil) to grind up their food.
Acknowledgement: Sara L Roggemann, Three Flowers Photography
Intestine
Once the food is ground up, it moves into the intestine where digestive4 fluids continue to break down the food so it can be absorbed.
Acknowledgement: Sara L Roggemann, Three Flowers Photography
Aortic arches
Most earthworm species5 have five aortic arches or ‘hearts’ that move blood around the body. The number of aortic arches varies amongst species.
Acknowledgement: Sara L Roggemann, Three Flowers Photography
Dorsal and ventral blood vessels
The dorsal blood vessel6 runs along the length of the upper side of the earthworm. It contracts and pumps blood to the aortic arches. The ventral7 blood vessel runs along the lower length of the earthworm.
Acknowledgement: Sara L Roggemann, Three Flowers Photography
Cerebral ganglion
The earthworm’s ‘brain’. Earthworms have a simple nervous system. The cerebral ganglion is connected to a ventral nerve cord that runs the length of the body. Each segment is connected to this cord, allowing earthworms to move and respond to light, touch, chemicals8, vibrations and more.
Acknowledgement: Sara L Roggemann, Three Flowers Photography
Circular muscles
Circular muscles surround each segment. When earthworms squeeze these muscles, they become long and thin. Circular muscles alternate with longitudinal muscles to help earthworms move.
Longitudinal muscles
Longitudinal muscles run the length of the earthworm. When these muscles contract, earthworms become short and fat. Longitudinal muscles alternate with circular muscles to help earthworms move.
- adaptation: A change in the structure or function of something. In biology, a change in a species, as a result of natural selection. Individuals with a particular feature (adaptation) are more likely to survive and reproduce than individuals without this feature.
- organic matter: The decomposed remains of living organisms and their waste products.
- saliva: A watery fluid produced by the salivary glands in the mouth. It is made up of water, mucus, amylase, lipase and sodium bicarbonate.
- digestive system: The group of organs that are involved in the breakdown of food in the body, which includes the stomach and intestines.
- species: (Abbreviation sp. or spp.) A division used in the Linnean system of classification or taxonomy. A group of living organisms that can interbreed to produce viable offspring.
- blood vessel: Any of the vessels, as arteries, veins, or capillaries, through which the blood circulates.
- ventral: The lower surface (the belly) of an animal.
- chemicals: Everything is made up of chemicals. All matter (anything made of atoms) can be called chemicals. They can be in any form – liquid, solid or gas. Chemicals can be a pure substance or a mixture.