How does the shape of the worm change as it move

When the circular muscles contract, the earthworm stretches, becoming longer and thinner. The earthworm uses its setae to anchor the front of its body in the soil. Now the longitudinal muscles contract and the earthworm becomes shorter and wider or it bends from one side to the other, pulling the body forward.

In earthworms, each segment can move independently, so that alternating contractions between the two different sets of muscles in many different segments create shape changes all along the body. This produces accordion-like body movements that help the worm push through soil and maneuver through small spaces within