Worms are many different distantly relatedbilateral animals that typically have a long cylindrical tube-like body, nolimbs, and usually noeyes.
Worms vary in size from microscopic to over 1 metre (3.3 ft) in length for marine polychaete worms (bristle worms);[1] 6.7 metres (22 ft) for the African giant earthworm,Microchaetus rappi;[2] and 58 metres (190 ft) for the marine nemertean worm (bootlace worm),Lineus longissimus.[3] Various types of worm occupy a small variety ofparasitic 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.
The term "helminth" is sometimes used to refer to parasitic worms. The term is more commonly used inmedicine, and usually refers to roundworms and tapeworms.
In taxonomy, "worm" refers to an obsolete grouping,Vermes, used byCarl Linnaeus andJean-Baptiste Lamarck for all non-arthropodinvertebrateanimals, now seen to bepolyphyletic. In 1758, Linnaeus created the firsthierarchical classification in hisSystema Naturae.[4] In his original scheme, the animals were one of three kingdoms, divided into the classes ofVermes,Insecta,Pisces,Amphibia,Aves, andMammalia. Since then the last four have all been subsumed into a single phylum, theChordata, while his Insecta (which included the crustaceans and arachnids) and Vermes have been renamed or broken up. The process was begun in 1793 by Lamarck, who called the Vermesune espèce de chaos (a sort of chaos)[a] and split the group into three new phyla, worms, echinoderms, and polyps (which contained corals and jellyfish). By 1809, in hisPhilosophie Zoologique, Lamarck had created 9 phyla apart from vertebrates (where he still had 4 phyla: mammals, birds, reptiles, and fish) and molluscs, namelycirripedes, annelids, crustaceans, arachnids, insects, worms,radiates, polyps, andinfusorians.[6]Chordates are remarkably wormlike by ancestry.[7]
Informal grouping
In the 13th century, worms were recognized in Europe as part of the category ofreptiles that consisted of a miscellany of egg-laying creatures, including "snakes, various fantastic monsters, lizards, assorted amphibians", as recorded byVincent of Beauvais in hisMirror of Nature.[8] In everyday language, the termworm is also applied to various other living forms such aslarvae,insects,millipedes,centipedes,shipworms (teredo worms), or even some vertebrates (creatures with a backbone) such asblindworms andcaecilians. Worms include several groups. The three main phyla are:
Platyhelminthes, includes theflatworms,tapeworms, andflukes. They have a flat, ribbon- or leaf-shaped body with a pair of eyes at the front. Some are parasites.
Nematoda, contains thethreadworms,hookworms and otherroundworms. Threadworms may be microscopic, such as the vinegar eelworm, or more than 1-metre (3 feet) long. They are found in damp earth, moss, decaying substances, fresh water, or salt water. Some roundworms are also parasites: theGuinea worm, for example, gets under the skin of the feet and legs of people living intropical countries.
Annelida, consists of the segmented worms, with bodies divided into segments or rings. Among these worms are theearthworms and thebristle worms of the sea.
Worms may also be calledhelminths, particularly inmedical terminology when referring toparasitic worms, especially theNematoda (roundworms) andCestoda (tapeworms). Hence, "helminthology" is the study of parasitic worms. When a human or an animal, such as adog or horse, is said to "have worms", it means that it is infested withparasitic worms, typicallyroundworms ortapeworms.Deworming is a method to kill off the worms that have infected a human or animal by givinganthelmintic drugs.
"Ringworm" is not a worm at all, but a skin fungus.
Lobopodians are an informal grouping of extinctpanarthropods from theCambrian to theCarboniferous that are often called worms or "worm-like animals" despite having had legs in the form of stubby lobopods. Likewise, the extantOnychophora are sometimes calledvelvet worms despite possessing stubby legs.
^Franklin-Brown, Mary (2012).Reading the world: encyclopedic writing in the scholastic age. Chicago London: The University of Chicago Press. p. 223;377.ISBN9780226260709.
