Worm


Worm

A worm is a common name given to a diverse group of invertebrate animals that have a long, soft body and no legs. There are hundreds of thousands of species of worms, 2,700 of these are earthworms. Animals which are commonly called worms include species of annelids, insects (their immature larva stage), and flatworms. Many marine and freshwater species, which are usually seen only by professional biologists, are recognized as "worms".

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 nonparasitic. 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.

Classification

In everyday language, the term "worm" is also applied to various other living forms such as larvae, insects, centipedes, shipworms (teredo worms), or even some vertebrates (creatures with a backbone) such as blindworms and caecilians. Worms can be divided into several groups,
*The first of these includes the flatworms. This phylum is called Platyhelminthes. They have a flat, ribbon- or leaf-shaped body with a pair of eyes at the front. Some are parasites.
*The second group contains the threadworms, roundworms, and hookworms. This phylum is called Nemotoda. Threadworms may be microscopic, such as the vinegar eelworm, or more than 1 meter (3 feet) long. They are found in damp earth, moss, decaying substances, fresh water, or salt water. Some roundworms are also parasites. The Guinea worm, for example, gets under the skin of the feet and legs of people living in tropical countries.
*The third group consists of the segmented worms, with bodies divided into segments, or rings. This phylum is called Annelida. Among these are the earthworms and the bristle worms of the sea.

There are hundreds of thousands of species that live in a wide variety of habitats other than soil. Over time this broad definition narrowed to the modern definition, although this still includes several different animal groups. Phyla that include worms include:

*Acanthocephala (spiny-headed worms)
*Annelida (segmented worms)
*Chaetognatha (arrow worms)
*Gnathostomulid (jaw worms)
*Hemichordata (acorn/tongue worms)
*Nematoda (roundworms)
*Nematomorpha (horsehair worms)
*Nemertea (ribbonworms)
*Onychophora (velvet worms)
*Phoronida (horseshoe worms)
*Platyhelminthes (flatworms)
*Priapulida (phallus worms)
*Sipuncula (peanut worms)The most common worm is the earthworm, a member of phylum Annelida. Earthworms in general have been around for 120 million years, evolving during the time of the dinosaurs. They enrich and aerate the soil; Charles Darwin found that worms turn over the top six inches (15 cm) of topsoil every 20 years. They lack a brain but have nerve centers (called ganglia); they also lack eyes but can sense light with photoreceptors. Worms are hermaphrodites (both sexes in one animal) but can cross fertilize.

Other invertebrate groups may be called worms, especially colloquially. In particular, many unrelated insect larvae are called "worms", such as the railroad worm, woodworm, glowworm, bloodworm, inchworm, mealworm, or silkworm.

Worms may also be called helminths, particularly in medical terminology when referring to parasitic worms, especially the Nematoda (roundworms) and Cestoda (tapeworms). Hence "helminthology" is the study of parasitic worms. When an animal, such as a dog, is said to "have worms", it means that it is infested with parasitic worms, typically roundworms or tapeworms.

"Ringworm" is not a worm at all, but a skin fungus.

Characteristics

[
Nematomorpha)] Worms usually have a cylindrical, flattened, or leaf-like body shape and are often without any true limbs or appendages. Instead, they may have bristles or fins that help them move. Many worms have sense organs that can detect environmental change. A few may even have light-sensing organs. Worms vary in size from less than 1 mm (0.04 inch) in certain aschelminths to more than 30 m (100 feet) in certain ribbon worms.

Some worms reproduce sexually. Hermaphroditism, the condition in which a single individual possesses both male and female reproductive parts, is common in many groups of worms. Asexual reproduction, whereby new individuals develop from the body cells of another, also occurs in some worms.

Worm species differ in their abilities to move about on their own. Many species have bodies with no major muscles, and cannot move on their own — they must be moved by forces or other animals in their environment. Many other species have bodies with major muscles and can move on their own; they are a type of muscular hydrostat. Many species of worms are decomposers; they break down dead plants and animals to return nutrients to the soil.

Image in Art

Worms are used as a metaphor of putrefaction (The Battleship Potemkin), death taking over life and death itself, an image of hell. There exists a mythological image of a never dying worm who is eternally eating dead people (Ligeia).

ee also

*Worm cast
*Worm charming


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Look at other dictionaries:

  • Worm — (w[^u]rm), n. [OE. worm, wurm, AS. wyrm; akin to D. worm, OS. & G. wurm, Icel. ormr, Sw. & Dan. orm, Goth. wa[ u]rms, L. vermis, Gr. ? a wood worm. Cf. {Vermicelli}, {Vermilion}, {Vermin}.] [1913 Webster] 1. A creeping or a crawling animal of any …   The Collaborative International Dictionary of English

  • WORM — ist die Abkürzung für „write once read many“ oder „write once read multiple“ (engl. „schreibe einmal, lese vielfach“). Sie bezeichnet Vorkehrungen in der Informationstechnik, die das Löschen, Überschreiben und Ändern von Daten ausschließen.[1]… …   Deutsch Wikipedia

  • Worm — bezeichnet den Begriff WORM (Write Once Read Multiple times = einmal beschreiben, mehrmals lesen ) aus der Speichertechnologie den Teil des Namens eines Computervirus, welchen ihn als Computerwurm deklariert Worm ist der Familienname folgender… …   Deutsch Wikipedia

  • WORM — (сокращение от англ. Write Once, Read Manу, также встречаются расшифровки: Write One, Read Multiple, Write Once, Read Mostly) носители информации, допускающие однократную запись и многократное чтение. К характерным представителям WORM… …   Википедия

  • worm — [wʉrm] n. [ME < OE wyrm, serpent, dragon, akin to Ger wurm < IE base * wer , to turn, bend > WARP, L vermis, worm] 1. any of many slender, soft bodied animals, some segmented, that live by burrowing underground, in water, or as parasites …   English World dictionary

  • Worm — Worm, v. t. 1. To effect, remove, drive, draw, or the like, by slow and secret means; often followed by out. [1913 Webster] They find themselves wormed out of all power. Swift. [1913 Webster] They . . . wormed things out of me that I had no… …   The Collaborative International Dictionary of English

  • worm — ► NOUN 1) an earthworm or other creeping or burrowing invertebrate animal having a long slender soft body and no limbs. 2) (worms) intestinal or other internal parasites. 3) a maggot regarded as eating dead bodies buried in the ground. 4)… …   English terms dictionary

  • worm|y — «WUR mee», adjective, worm|i|er, worm|i|est. 1. having worms; containing many worms: »wormy apples. efn>damaged by worms; worm eaten: »wormy wood. 2 …   Useful english dictionary

  • Worm — Worm, v. i. [imp. & p. p. {Wormed}; p. pr. & vb. n. {Worming}.] To work slowly, gradually, and secretly. [1913 Webster] When debates and fretting jealousy Did worm and work within you more and more, Your color faded. Herbert. [1913 Webster] …   The Collaborative International Dictionary of English

  • WORM-FM — 101.7FM 101theWorm is a country radio station based in Savannah, Tennessee. WORM FM serves Savannah and the surrounding area with an ERP of 3000 watts at 101.7FM. WORM FM is owned by Gerald W. Hunt …   Wikipedia

  • WORM — 〈[wɔ:m] f. 10; EDV; Abk. für engl.〉 Write Once Read Many Times; optische Speicherplatte mit hohem Speichervolumen [engl., „schreib einmal, lies mehrfach“] * * * WORM,   Write once read Multiple …   Universal-Lexikon


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