worm lizard, partially or entirely limbless burrowing lizard of the family Amphisbaenidae. All worm lizards lack hind limbs and most species lack forelimbs as well. Except for their size, they are very similar in appearance to earthworms, with cylindrical bodies ringed by shallow grooves. Their eyes and ears are covered by skin. Most are about a foot (30 cm) long. Members of many species remain underground most of their lives, feeding on earthworms, spiders, and insects. Worm lizards are found in tropical and warm temperate areas of Africa, SW Asia, S Europe, and the Americas. The only species found in the United States is the Florida worm lizard, Rhineura floridana, of N and central Florida, which attains a length of 11 in. (28 cm). Worm lizards are classified in the phylum Chordata, subphylum Vertebrata, class Reptilia, order Squamata, family Amphisbaenidae.

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.

sand worm, name applied to a number of marine sand-dwelling Worms used as bait in fishing. See Class Polychaeta under Annelida.

ribbon worm: see Nemertinea.

measuring worm: see inchworm.

horsehair worm, worm of the class Nematomorpha.

apple worm: see codling moth.

acorn worm: see Hemichordata.

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. Seealso fluke, pinworm, polychaete, rotifer, tapeworm, tube worm.

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Any of about 90 species of free-living terrestrial invertebrates in the class Onychophora (sometimes considered a phylum). They are sometimes called velvet worms for their velvety skin. The common genus Peripatus occurs in the West Indies, Central America, and northern South America. Onychophorans are slender and segmented; each segment has a pair of short legs. Species range from 0.6 to 6 in. (14–150 mm) long. They live in humid, hidden spots: in forest litter, wood crevices, termite nests, or the soil, sometimes to a depth of more than 3 ft (1 m). They use their jaws to open captured prey (often small insects) and suck out the juices.

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Any of numerous species of sedentary, solitary or colonial, marine worms that spend their entire life in a tube made from special secretions or from sand grains glued together. Found worldwide, tube worms range from less than an inch (25 mm) to more than 20 ft (6 m) long. The bottom of the tube is attached to the seafloor; the mouth and tentacles are at the upper, open end. The worm breathes through gills, the tentacles, or the body wall. The tentacles, variously arranged, are used to filter-feed aquatic plants and animals. Tube worms occur in the annelid class Polychaeta and in the phyla Phoronida and Pogonophora. Many, mostly unnamed, forms live in deep-ocean vent communities.

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Any member of a phylum (Annelida) of invertebrate animals that possess a body cavity (coelom), movable bristles (setae), and a body divided into segments by crosswise rings. Known as segmented worms, annelids are divided into three classes: marine worms (Polychaeta; see polychaete), earthworms (Oligochaeta), and leeches (Hirudinea).

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or roundworm

Any of more than 15,000 named and many more unnamed species of worms in the class Nematoda (phylum Aschelminthes). Nematodes include plant and animal parasites and free-living forms found in soil, freshwater, saltwater, and even vinegar and beer malts. They are bilaterally symmetrical and usually tapered at both ends. Some species have separate sexes; others are hermaphroditic. They range from microscopic to about 23 ft (7 m) long. Nematode parasites can occur in almost any body organ but are most common in the digestive, circulatory, or respiratory system. Hookworms, pinworms, and eelworms are nematodes. Seealso filarial worm, guinea worm, trichina.

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or cankerworm or inchworm

Larva of any member of a large, widespread group (mostly in the family Geometridae, with some in the family Noctuidae) of moths. Loopers move in a characteristic “inching” or “looping” gait by extending the front part of the body and bringing the rear up to meet it. Resembling twigs or leaf stems, they feed on foliage, and can seriously damage or destroy trees.

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Distinctive green, white-lined larva, or caterpillar (Trichoplusia ni), of the owlet moth family (Noctuidae). Like other loopers, it moves in an “inching” motion. It is an economic pest of cabbages and associated crops, particularly in the U.S. and Europe. The adults, known as Ni moths, migrate considerable distances. They are mottled brown with a pale Y-shaped mark on each forewing. The typical adult wingspan is about 1 in. (25 mm).

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Any of about 5,400 species of marine worms of the annelid class Polychaeta, having a segmented body with many setae (bristles) on each segment. Species, often brightly coloured, range from less than 1 in. (2.5 cm) to about 10 ft (3 m) long. Most body segments bear two bristly parapodia (lobelike outgrowths). The head has short sensory projections and tentacles. Adults may be free-swimming or sedentary; larvae are free-swimming. Found worldwide, polychaetes are important for turning over sediment on the ocean bottom. One species, the bloodworm, is a popular saltwater fish bait. Seealso tube worm.

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or hairworm or gordian worm

Any of about 250–300 species (class Nematomorpha, or Gordiacea; phylum Aschelminthes) of long, thin worms. The young are parasites in arthropods; the adults are free-living in the sea or in freshwater. The hairlike body sometimes grows to a length of about 39 in. (1 m).

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or medina worm or dragon worm

Nematode (Dracunculus medinensis) that is a common parasite of humans and other mammals in tropical Asia and Africa and has been introduced into the West Indies and tropical South America. The female grows to 20–48 in. (50–120 cm) long; the male, which dies upon mating, is only about 0.5–1.1 in. (12–29 mm) long. Both sexes live in the connective tissue of the host animal. Humans become infected when they drink water containing tiny crustaceans (e.g., copepods) that have eaten guinea-worm larvae. The disease the guinea worm carries, called dracunculiasis, can be extremely debilitating and painful.

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Any of a group of parasitic nematodes that usually require two hosts to complete the life cycle: an arthropod and another animal, which is bitten by the arthropod. The female worm produces large numbers of microscopic, active embryos, called microfilariae, that pass into the bloodstream of the primary host. These enter the body of an insect when it bites the infected animal; within the insect the microfilariae grow into larvae, which are passed to an animal the insect bites, where they complete their growth. Seealso heartworm.

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