Worm 33659 225687366 2008-07-14T22:16:00Z Mauler90 7379685 Reverted edits by [[Special:Contributions/12.147.118.135|12.147.118.135]] ([[User talk:12.147.118.135|talk]]) using [[User:MichaelBillington/MWT|MWT]] {{Otheruses}} {{Refimprove|date=February 2008}} 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 about 4,400 species of worms, about half being [[earthworms]]. Animals which are commonly called worms include species of [[annelids]], [[insects]] (their immature '''[[larva]]''' stage), and [[Platyhelminthes|flatworms]]. Many marine and freshwater species, which are usually seen only by professional biologists, are recognized as "worms". Worms commonly are seen on the sidewalk after a rainstorm, and often die of drying out or being trampled on by humans. ==Distribution and habitat== [[Image:Earthworm.jpg|thumb|Common [[earthworm]]]] 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. 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. ==Classification== In everyday language, the term ''worm'' is also applied to various other living forms such as [[larva]]e, [[insects]], [[centipedes]], [[shipworm]]s (teredo worms), or even some vertebrates (creatures with a backbone) such as [[Anguis fragilis|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. Major [[phyla]] that include worms include: [[Image:Regenwurm1.jpg|thumb|right|200px|An [[earthworm]]]] *[[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) [[Image:Miñoca.earthworm.jpg|thumb|100px|left]] The most common worm is the [[earthworm]], a member of [[Phylum (biology)|phylum]] [[Annelida]]. Earthworms in general have been around for 120 million years, evolving during the time of the [[dinosaur]]s. 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 [[Ocellus|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]] [[larva]]e are called "worms", such as the [[railroad worm]], [[woodworm]], [[glowworm]], [[Midge (insect)|bloodworm]], [[inchworm]], [[mealworm]], or [[silkworm]]. Worms may also be called '''helminths''', particularly in [[medical]] terminology when referring to [[parasitic worm]]s, 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 [[roundworm]]s or [[tapeworm]]s. "[[Ringworm]]" is not a worm at all, but a skin fungus. ==Characteristics== [[Image:Paragordius tricuspidatus.jpeg|thumb|right|200px|''Paragordius tricuspidatus'' ([[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. ==See also== *[[Worm cast]] *[[Worm charming]] [[Category:Animals]] [[gn:Yso]] [[ay:Laq'u]] [[ba:Селәүсен]] [[bg:Червей]] [[ca:Cuc]] [[cs:Červ]] [[cy:Llyngyren]] [[da:Orm]] [[de:Würmer]] [[et:Ussid]] [[el:Σκουλήκι]] [[es:Gusano]] [[eo:Vermo]] [[eu:Har]] [[fr:Ver]] [[gd:Cnuimh]] [[gl:Verme]] [[hr:Crvi]] [[iu:ᖁᐱᓪᕈᖅ/qupilruq]] [[it:Verme]] [[he:תולעים]] [[pam:Bulati]] [[kw:Pryv]] [[la:Vermes]] [[lt:Kirmėlė]] [[ms:Cacing]] [[nah:Ocuilin]] [[nl:Worm (dieren)]] [[ja:虫]] [[no:Makk]] [[nn:Makk]] [[oc:Vèrm]] [[pl:Robaki]] [[pt:Verme]] [[ro:Vierme]] [[qu:Kuru]] [[simple:Worm]] [[tr:Solucan]] [[uk:Черви]] [[yi:וואָרעם]] [[zh:蠕虫]] [[tl:Uod]]