Explain the movement of an earthworm.

Locomotion or Movement in Earthworm

An earthworm secretes a slimy substance called mucus over which it slides or moves by using repeating circular and longitudinal muscles, as well as bristles which are known as setae. 

The earthworm pushes the setae out of its body to grab the soil around it, and first extends the front part of the body, keeping the rear portion fixed to the ground, then it fixes the front end and releases the rear end. After that, it shortens the body and pulls the rear end forward.

By this process, it covers a small distance.