Nematoda
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Roundworm, also nematode, common name for any of a phylum of unsegmented terrestrial, freshwater, or marine worms. Roundworms are almost worldwide in distribution and are abundant in the surface layers of soils. Many of them are economically and medically harmful, living as parasites in plants and animals, including humans. Roundworm infections are common and frequently go unnoticed, but several species cause serious diseases.
Roundworms are cylindrical, tapering animals with simple bodies consisting of an interior gut and a muscular outer wall, separated by a fluid-filled cavity called a pseudocoel (see Animal: Coelom). The outer wall secretes an elastic cuticle that is molted four times during the animal's lifetime. Species range in size from microscopic to about 10 cm (about 4 in) long. Most species have separate sexes, but a few are hermaphroditic; fertilization is internal. The young roundworms, which resemble the adults, develop without metamorphosis.
Although numerous roundworms are free-living, the parasitic forms are of greatest economic interest. One important group, the ascaroid nematodes, includes the threadworms and the common worm of puppies. Another contains the eelworms, which produce root knot of cotton, and forms that produce earcockle of wheat. Other, medically significant forms of roundworm include the various genera known as hookworm; the filaria, which cause elephantiasis; the trichina worm, the cause of trichinosis; and the whipworm, which infests the human intestine.
Scientific classification: Roundworms make up the phylum Nematoda. Threadworms belong to the genus Ascaris. The common worm of puppies is classified as Toxocara canis. Eelworms belong to the genus Heterodera, the forms that produce earcockle of wheat belong to the genus Tylenchus, and the trichina worm belongs to the genus Trichinella. The human whipworm is classified as Trichuris trichiura.
Roundworm, also nematode, common name for any of a phylum of unsegmented terrestrial, freshwater, or marine worms. Roundworms are almost worldwide in distribution and are abundant in the surface layers of soils. Many of them are economically and medically harmful, living as parasites in plants and animals, including humans. Roundworm infections are common and frequently go unnoticed, but several species cause serious diseases.
Roundworms are cylindrical, tapering animals with simple bodies consisting of an interior gut and a muscular outer wall, separated by a fluid-filled cavity called a pseudocoel (see Animal: Coelom). The outer wall secretes an elastic cuticle that is molted four times during the animal's lifetime. Species range in size from microscopic to about 10 cm (about 4 in) long. Most species have separate sexes, but a few are hermaphroditic; fertilization is internal. The young roundworms, which resemble the adults, develop without metamorphosis.
Although numerous roundworms are free-living, the parasitic forms are of greatest economic interest. One important group, the ascaroid nematodes, includes the threadworms and the common worm of puppies. Another contains the eelworms, which produce root knot of cotton, and forms that produce earcockle of wheat. Other, medically significant forms of roundworm include the various genera known as hookworm; the filaria, which cause elephantiasis; the trichina worm, the cause of trichinosis; and the whipworm, which infests the human intestine.
Scientific classification: Roundworms make up the phylum Nematoda. Threadworms belong to the genus Ascaris. The common worm of puppies is classified as Toxocara canis. Eelworms belong to the genus Heterodera, the forms that produce earcockle of wheat belong to the genus Tylenchus, and the trichina worm belongs to the genus Trichinella. The human whipworm is classified as Trichuris trichiura.
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