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Phylum Nematoda, within Kingdom Animalia, consists completely of roundworms. Roundworms are cylindrical worms which appear nearly to have no head. On closer observation, however, one can see that the anterior end of the roundworm, the head, is actually slightly more blunt than the posterior, the tail. A cuticle, or tough outer layer of nonliving skin, protecting the nematode from drying or being crushed. The cuticle covers the entire body of a roundworm. Nematodes are pseudocoelomates. They have a pseudocoelom, an internal body space surrounding the endoderm tissue of the digestive tract and surrounded by the mesoderm tissue. This distinguishes them from coelomates, whose body cavity is surrounded entirely by mesoderm tissue. The Nematodes have a complete alimentary canal with a separate mouth and anus and traversing the entire length of the organism. This distinguishes them from organisms in the phylum Platyhelminthes, who have only an incomplete digestive tract. There are two primary types of roundworms: parasitic and free-living. Parasitic roundworms live within the tissues of plants and the body fluid or tissues of other animals. They survive off of their host organism, and generally do harm to the organism. Free-living roundworms are more abundant than parasitic roundworms, and just as harmful. They destroy plant roots, causing the entire plant to die, and can deprive an animal of the necessary nutrients it needs to survive. Free-living roundworms, unlike the parasites, live virtually every place on earth where other creatures live, and many of them feed off rotting organic matter. Despite the great number of roundworms, and the variety of ecosystems where they live, nearly all roundworms are alike in their general body structure: a cylindrical body, a tapered tail and a blunt head (6).