Locomotion in Helix aspersa

The pedal waves in Helix aspersa move faster than the foot of the animal. On the other hand, a histological study of the foot could not identify an organized muscular structure expected to be capable of wave construction. Instead, a non-organized tissue with relatively few muscle cells and many collagen fibers mixed with vessels and empty cavities was found. We could demonstrate that the movement of the waves was uncoupled from the movement of the foot and that the forward displacement of the snail is due to rhythmic fluid accumulation under pressure. This pressure generates a force in backward direction on the substratum, which in turn is used as push off by the animal to move in a forward direction. The snail does not crawl, the waves move independently from the foot sole, and the animal glides smoothly without changing the length or the shape of the foot. The problem how waves are constructed starting from the available muscular material is not solved. We advance a cautious hypothesis that it happens by a cyclic reversible recruitment of cells at the moving front and a corresponding dropping off at the rear.