Nematomorpha

Nematomorpha

(nĕm'ətəmôr`fə), small (about 230 species) phylum of pseudocoelomates; the horsehair worms. Most are very slender, elongated creatures found in ponds and streams, whose larvae live as parasites in arthropods. They emerge as adults for a brief time, then mate and die. A small number are planktonic in marine habitats and live as larvae in crabs or shrimps. Adults are simplified externally and internally; they have no excretory or circulatory systems and only a vestigial digestive tract. The female produces long strings of eggs. After hatching, the larva penetrates any convenient aquatic animal, but its development stops until it has found its way into an appropriate host, typically an insect. The adult nematomorph emerges when the host is in or near water; it molts once after emerging and takes up its brief adult existence.

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Nematomorpha

A phylum of worms that was formerly considered to be a class of the phylum Aschelminthes; commonly called the hairworms, and closely allied to the nematodes. The adults are free-living in aquatic habitats, while the juveniles are parasitic in arthropods. The nematomorphs are found all over the world. They are divided into two classes, the Nectonematoidea and Gordioidea, with a total of 225 species. See Nemata

The body is long and slender with a maximum length of 5 ft (1.5 m) and a diameter of 0.02–0.12 in. (0.5–3 mm). The females are longer than the males. The posterior end may be rounded with a terminal cloaca, or it may form two or three lobes in a forklike structure. The body color is yellowish, brown, or almost black. The body wall consists of three layers: an outer, rather thick fibrous cuticle; an epidermis consisting of a single layer of cells; and innermost, a muscle layer with longitudinal fibers only.

The sexes are always separate, and the gonads are paired and stringlike extending the length of the body. The eggs are laid in water in strings, and the adults die after egg laying. When hatched, the larvae swim to an aquatic arthropod. They penetrate the body wall of the host by means of their characteristic proboscis, which is armed with hooks and three long stylets. The gradual development in the host lasts some months without any metamorphosis. When they are mature, the worms leave the host.

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.

Nematomorpha

[‚nem·əd·ə′mȯr·fə]

(invertebrate zoology)

A group of the Aschelminthes or a separate phylum that includes the horsehair worms.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.