All roundworms have a similar structure: an elongated body shape, a round cross-section (hence the name of the type), bilateral symmetry.
The body of Roundworms consists of three layers of cells: ectoderm, endoderm, and mesoderm (that is, they are three-layer animals).
The internal (primary) cavity of the body is filled with a fluid under pressure and ensures the constancy of the body shape.
The musculature is located along the body by four longitudinal bands.
Inside the body are the digestive, excretory and reproductive systems. In the body, they have a through intestinal tube, which begins at the front end of the body with the mouth opening and ends with the anus (which first appeared in the course of evolution).
Usually roundworms are dioecious.
The respiratory and circulatory systems are absent.
Nerve cells are concentrated in the form of cords in the muscle ridges; there is a nerve ring at the front end of the body.
Currently, more than 20 thousand species of roundworms are known. They can be found in all habitats. Free-living are found at the bottom of the seas and oceans, in fresh waters and soil. Many roundworms have adopted the decaying organic remains of animals and plants for life. There are many parasites among roundworms that live in organisms of plants and animals, for example, roundworms.
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