How do larger flatworms crawl using waves of muscular contraction?

Larger flatworms utilize a method of movement known as pedal locomotion to crawl, as ciliary activity is insufficient for their size. In this process, the animal generates waves of muscular contraction through its ventral musculature, which remains in contact with the bottom surface.1

These pedal contraction waves can be categorized into two types:

• Direct waves: These move in the same direction as the animal. As a wave reaches a muscle, it contracts and lifts a small part of the body, which is then carried forward and set down anterior to its original position.1
• Retrograde waves: These move in the direction opposite to the animal's movement. As the wave approaches, the body area adjacent to it is extended upward; the body surface within the contraction area then anchors to the surface, allowing the rest of the body to be pulled forward.1

By using these muscular contractions, larger flatworms are able to crawl in a snail-like fashion.2