Earthworms' bodies are cylindrical (different from linear animals), with symmetrical sides and segmented phenomena: they are composed of 100 sections, and after the eleventh section, there is a back hole in the center of each section; It has no bones, belongs to invertebrates, and its body surface is bare without cuticle.

The role of bristles: when the earthworm advances, the bristles at the back of the body are fixed. At this point, the annular muscle contracts, the longitudinal muscle relaxes, and the body wriggles forward; Then fix the bristles at the front end of the body. At this point, the longitudinal muscles contract, the annular muscles relax, and the body shortens forward. Therefore, the earthworm moves forward through the alternating contraction and relaxation of muscles, with bristles, so the moving organs of the earthworm are bristles and muscles.

Extended data:

Muscle structure of earthworm;

The muscle of earthworm belongs to twill muscle, which generally accounts for about 40% of the whole body volume. It is muscular and flexible. When the longitudinal muscle layer of some segments of earthworm contracts and the annular muscle layer relaxes, the segments of earthworm become thicker and shorter, and the oblique bristles on the body wall protrude outward and are inserted into the surrounding soil.

At this time, the annular muscle layer of the former section contracts, the longitudinal muscle layer relaxes, this section becomes thinner and longer, and the bristles retract, getting rid of contact with the surrounding soil, thus being supported by the bristles of the latter section to push the body forward. In this way, the muscle contraction wave is gradually transmitted from front to back along the longitudinal axis of the body.

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