When an animal or human is said to "have worms", it means that it is infested with parasitic worms, typically roundworms or tapeworms. 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. Invertebrate animals commonly called "worms" include annelids ( earthworms and marine polychaete or bristle worms), nematodes ( roundworms), platyhelminthes ( flatworms), marine nemertean worms (" bootlace worms"), marine Chaetognatha ( arrow worms), priapulid worms, and insect larvae such as grubs and maggots.
Most animals called "worms" are invertebrates, but the term is also used for the amphibian caecilians and the slowworm Anguis, a legless burrowing lizard. The name stems from the Old English word wyrm. In biology, "worm" refers to an obsolete taxon, vermes, used by Carolus Linnaeus and Jean-Baptiste Lamarck for all non- arthropod invertebrate animals, now seen to be paraphyletic. Free-living worm species do not live on land but instead live in marine or freshwater environments or underground by burrowing. Various types of worm occupy a small variety of parasitic niches, living inside the bodies of other animals. Worms vary in size from microscopic to over 1 metre (3.3 ft) in length for marine polychaete worms (bristle worms) 6.7 metres (22 ft) for the African giant earthworm, Microchaetus rappi and 58 metres (190 ft) for the marine nemertean worm (bootlace worm), Lineus longissimus.
Worms are many different distantly related bilateral animals that typically have a long cylindrical tube-like body, no limbs, and no eyes (though not always). Lumbricus terrestris, an earthworm White tentacles of Loimia medusa, a spaghetti worm These worms are mostly carnivores or scavengers.For other uses, see Worm (disambiguation). \): Marine flatworms can be brightly colored, such as this one from the class Turbellaria.
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