Final answer:
An earthworm moves through the contraction of circular and longitudinal muscles, following a pattern known as peristalsis, supported by its hydrostatic skeleton.
Step-by-step explanation:
An earthworm has two types of muscles that aid in movement: circular and longitudinal. The circular muscles, when contracted, cause the earthworm to elongate, allowing it to extend the anterior end of the body and anchor into the soil.
In contrast, when the longitudinal muscles contract, the earthworm becomes shorter and thicker, pulling the posterior end forward. This movement pattern is known as peristalsis, which is very efficient for earthworms as they burrow through the soil and navigate their environment.
This type of locomotion is supported by the earthworm's hydrostatic skeleton, consisting of a fluid-filled coelom that provides structure for muscle attachment and movement.