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worm, common name for various unrelated invertebrate animals with soft, often long and slender bodies. Members of the phylum Platyhelminthes, or the flatworms, are the most primitive; they are generally small and flat-bodied and include the free-living planarians (of the class Turbellaria) as well as the parasitic flukes (class Trematoda) and tapeworms (class Cestoda). The nemertines, or ribbon worms (phylum Nemertinea), are often colorful marine carnivores with an extensible proboscis. The smallest species are only a fraction of an inch (less than 2.5 cm) long, while giants of the group range up to 90 ft (27 m) and are the longest of all invertebrates. Pseuodcoelomate worms include those in the phyla Rotifera, Gastrotricha, Kinorhyncha, Nematoda, and Nematomorpha. Of these, the largest phylum is the nematodes, which are probably the most numerous multicellular animals. Also called roundworms and threadworms, the nematodes include widespread free-living species as well as parasites, such as the hookworm. Other parasitic nematodes include Filaria, the cause of filariasis, which may result in elephantiasis; Trichinella, the cause of trichinosis; Ascaris, an intestinal parasite of humans, horses, and pigs; the pinworm, a parasite common in children; the Guinea worm, Dracunculus medinensis, now restricted to N sub-Saharan Africa, which is ingested as a larva in water and slowly emerges when full grown (up to 3 ft/91 cm) through a painful sore in the skin; and various other species that are agricultural pests. Like the nematodes, the hairworms, or horsehair worms, are unsegmented, but they are grouped separately in the phylum Nematomorpha. The larvae are parasitic, first in the bodies of aquatic insects and then within grasshoppers or beetles. The adult is about 6 in. (15 cm) long and covered with brown chitin, giving it a stiff appearance; since the worms were frequently found in watering troughs, superstition had it that they developed from horsehairs. The annelid worms (phylum Annelida) have segmented bodies, distinct heads, digestive tubes, circulatory systems, and brains. Appendages on each segment are used for walking or swimming. They include the earthworm, of the class Oligochaeta, the leech (class Hirudinea), and the marine annelids of the class Polychaeta. The sea mouse, the clam worm, and the feather duster worm belong to the latter group. The shipworm is a type of clam. The larvae of many insects are popularly called worms. Moth and butterfly larvae can be distinguished from adult animals called worms by the presence of several pairs of fleshy appendages at the rear end of the body (see caterpillar). However, other insect larvae are completely legless, while still others are equipped with six pairs of legs, as in adult insects (see larva). Insect larvae known as worms include the armyworm, bagworm, cutworm, and inchworm.

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worm

Any of thousands of species of unrelated invertebrate animals that typically have a soft, slender, elongated body with no appendages. The major phyla are Platyhelminthes (flatworms), Annelida (annelids, or segmented worms), Nemertea (ribbon worms), Acanthocephala (spiny-headed worms), and Aschelminthes (nematodes and others). There are several minor phyla. Length ranges from microscopic (e.g., some aschelminths) to more than 100 ft (30 m) (some ribbon worms). Worms are found worldwide on land and in water. They may be parasitic or free-living and are important as soil conditioners, parasites, and a link in the food chain in all ecosystems. See also fluke, pinworm, polychaete, rotifer, tapeworm, tube worm.

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(1) A destructive program that replicates itself throughout a single computer or across a network, both wired and wireless. It can do damage by sheer reproduction, consuming internal disk and memory resources within a single computer or by exhausting network bandwidth. It can also deposit a Trojan that turns a computer into a zombie for spam and other malicious purposes. Very often, the terms "worm" and "virus" are used synonymously; however, worm implies an automatic method for reproducing itself in other computers. See virus, logic bomb, smartphone virus, Worm.ExploreZip virus and Morris worm.

(2) A program that moves through a network and deposits information at each node for diagnostic purposes or causes idle computers to share some of the processing workload. See ethical worm.

(3) (WORM) (Write Once Read Many) An optical disc that can be recorded only once. Updating requires destroying the existing data (all 0s made 1s), and writing new data to an unused part of the disk.

There are two kinds of WORM technologies. Ablative large-format (12-14") WORM is the traditional type, which makes a permanent change in the optical material. Continuous composite write (CCW) WORM is a mode in multifunction 5.25" optical (MO) drives that emulates a WORM drive. The data are not permanently changed, but the drive contains firmware that ensures that recorded areas are not rewritten. See optical disc.

WORM Cartridges

Large-format 12-14" WORM drives have used the ablative technology. Magneto-optic drives have firmware that turns MO media into write-once disks.

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1.		WORM - Write-Once Read-Many
2.	(networking, security)	worm - (From "Tapeworm" in John Brunner's novel "The Shockwave Rider", via XEROX PARC) A program that propagates itself over a network, reproducing itself as it goes. Compare virus. Nowadays the term has negative connotations, as it is assumed that only crackers write worms. Perhaps the best-known example was the Great Worm. Compare Trojan horse.