Worm

A worm is a bilateral animal. It usually has no arms or legs, and a slender cylinder-like body.

Worms come in many different sizes. Some species are very small, while the bootlace worm has been known to grow up to nearly 60 meters (almost 200 feet).^[1] One of the best-known types of worms are earthworms.

Worm is not a term used by itself in animal classification. There are worms which belong to several phyla. Examples of words include: Annelids, nematodes, platyhelminthes, ribbon worms, arrow worms, priapulid worms, and some insect larvae. They are all animals which may be called 'worms'.

The Platyhelminthes includes the flatworms, tapeworms, and flukes. They have a flat, ribbon or leaf-shaped body with a pair of eyes at the front. Some are parasites.
The second group has the threadworms, roundworms, and hookworms. This phylum is called the Nematoda.
The third group is the segmented worms: the Annelids. Their bodies are divided into segments or rings. Among these worms are the earthworms and the bristle worms of the sea.

Many unrelated insect larvae are called "worms", such as the railroad worm, woodworm, glowworm, bloodworm, inchworm, mealworm, silkworm, and woolly bear worm.

Worms may also be called helminths, particularly in medical terminology when referring to parasitic worms, especially the Nematoda (roundworms) and Cestoda (tapeworms). "Helminthology" is the study of parasitic worms. When a human or an animal, such as a dog or horse, is said to "have worms", it means that it is infested with parasitic worms, typically roundworms or tapeworms. Deworming kills off the worms that have infected a human or animal by giving anthelmintic drugs.

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

Informal grouping[change | change source]

Worms include several groups. The three main phyla are:

Platyhelminthes, includes the flatworms, tapeworms, and flukes. They have a flat, ribbon- or leaf-shaped body with a pair of eyes at the front. Some are parasites.
Nematoda, contains the threadworms, roundworms, and hookworms. 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: the Guinea worm, for example, gets under the skin of the feet and legs of people living in tropical countries.
Annelida, consists of the segmented worms, with bodies divided into segments or rings. Among these worms are the earthworms and the bristle worms of the sea.