Why can polychaetes move well not only in water but also on the surface, but also in the thickness

Why can polychaetes move well not only in water but also on the surface, but also in the thickness of the soil and inside the tubes?

Polychaetes are annelids, specifically representatives of the polychaete class. These worms are characterized by the presence of bundles of bristles on the sides of the body (hence the name of the class). Thanks to the bristles, the worm can move over uneven surfaces. That is, inside the soil and pipes. And thanks to alternating contractions to the longitudinal muscles with the annular muscles, which are part of the skin – muscle sac, the animal is able to move in the water column and on the surface of the earth.