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The term worm is used in everyday language to describe many different distantly related animals that typically have a long cylindrical tube-like body and no limbs. Worms vary in size from microscopic to over in length for marine polychaete worms (bristle worms),〔(【引用サイトリンク】title=Cornwall – Nature – Superstar Worm )〕 for the African giant earthworm, ''Microchaetus'',〔Keely Parrack (21 June 2005) ("The Mighty Worm" ). ''Worm Digest''.〕 and for the marine nemertean worm (bootlace worm), ''Lineus longissimus''.〔Mark Carwardine (1995) ''The Guinness Book of Animal Records''. Guinness Publishing. p. 232.〕 Various types of worm occupy a small variety of parasitic niches, living inside the bodies of other animals. Free-living worm species do not live on land, but instead live in marine or freshwater environments, or underground by burrowing. In biology, "worm" refers to an obsolete taxon (''vermes'') used by Carolus Linnaeus and Jean-Baptiste Lamarck for all non-arthropod invertebrate animals, and stems from the Old English word ''wyrm''. Most animals called "worms" are invertebrates, but the term is also used for the amphibian caecilians and the slow worm ''Anguis'', a legless burrowing lizard. Invertebrate animals commonly called "worms" include annelids (earthworms), nematodes (roundworms), platyhelminthes (flatworms), marine polychaete worms (bristle worms), marine nemertean worms ("bootlace worms"), marine Chaetognatha (arrow worms), priapulid worms, and insect larvae such as grubs and maggots. Worms may also be called helminths, particularly in medical terminology when referring to parasitic worms, especially the Nematoda (roundworms) and Cestoda (tapeworms) which reside in the intestines of their host. When an animal or human is said to "have worms", it means that it is infested with parasitic worms, typically roundworms or tapeworms. == Distribution and habitat == Worms live in almost all parts of the world including marine, freshwater, and terrestrial habitats. Some worms living in the ground help to condition the soil (e.g., annelids, aschelminths). Many thrive as parasites of plants (e.g., aschelminths) and animals, including humans (e.g., platyhelminths, aschelminths). Several other worms may be free-living, or non parasitic. There are worms that live in freshwater, seawater, and even on the seashore. Ecologically, worms form an important link in the food chains in virtually all the ecosystems of the world. In the United States, the average population of worms per acre is 53,767.〔 ("Average US Worm Population" ) ''Popular Mechanics''], October 1950, p. 158, small article bottom of page.〕 Northern forests in America were once worm free.〔Charles C. Mann (May 2007) (America, Found and Lost ). National Geographic 〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「worm」の詳細全文を読む スポンサード リンク
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