How do circular and longitudinal muscles work together in earthworm movement?

Earthworms move through a process of peristaltic contractions that rely on the interaction between their body wall muscles and the fluid-filled coelom. The body wall contains an outer layer of circular muscles and an inner layer of longitudinal muscles.1

These muscles work together in a coordinated cycle to facilitate movement:

• Elongation: When the circular muscles contract, the segment becomes thinner and elongates, pushing the anterior end forward.12
• Shortening: When the longitudinal muscles contract, the segment shortens and widens, which helps anchor that part of the body against the burrow wall.1

This process is highly organized: the muscles of each segment contract in sequence, creating waves of contraction that pass along the body. During this cycle, the coelomic fluid acts as a hydrostatic skeleton, providing a substance against which the muscles can work. Additionally, the earthworm uses setae (bristles) to anchor segments to the surface, preventing backward slippage while the longitudinal muscles contract. By alternating these contractions, the worm is able to crawl slowly or burrow effectively.12