Nematoda (Roundworms)


The Nematoda are a group of nonsegmented worm‐like invertebrates that occur worldwide in a wide range of habitats, including fresh and salt waters, soil, plants and animals. They are one of the most abundant group of invertebrates on the face of the earth and rival the arthropods in biodiversity and species abundance. Their estimated numbers range from 1.5 billion in an upper 20 mm in 1.6 hectares of marine beach sand to 380 million in a square metre of leaf litter. Evidence from fossils and extant forms indicate that they evolved in the sea and came on land by probably moving up brackish estuaries into freshwater habitats. Although many of the plant parasites are considered pests and controlled with nematicides, other nematodes are important in controlling agricultural and medically important insect pests and still others have been used as experimental organisms in genetics.

Key Concepts:

  • Nematodes are the most successful group of the Ecdysoma, or pseudocoelomate bilateria.

  • Nematodes are one of the most abundant groups of invertebrates.

  • Some 20 000 nematode species have been described.

  • Estimates for species diversity range from 100 000 to 10 million.

  • Plant parasitic nematodes can be important agricultural pests.

  • Many nematodes live in the bodies of humans and their pets.

Keywords: nematodes; roundworms; plant parasites; metazoans; invertebrates

Figure 1.

Basic anatomy of nematodes as illustrated by a female (left) and male (right) of Rhabditis sp., a secernentean, microbotrophic nematode of the family Rhabditidae, order Rhabditida. A, anus; B, bursa; Bb, basal bulb of pharynx; C, corpus of pharynx; E, egg; Ep, excretory pore; G, gubernaculum; I, intestine; N, nerve ring; O, ovary; R, rectum; Rg, rectal gland; S, spicule; Sp, sperm; St, stoma; T, testis; U, uterus; V, vulva; Va, vagina; Vd, vas deferens.

Figure 2.

Adults of Ascaris lumbricoides removed from a child who died as a result of the infection. This nematode was the first to be recorded approximately 1550 BC.

Figure 3.

Long, white coils of a mermithid nematode that developed inside the body cavity of a spider. The host died after the nematode exited.



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Further Reading

Andrássy I (2005) Free‐living nematodes of Hungary (Nematoda errantia). I. Budapest: Hungarian Natural History Museum and Systematic Zoology Research Group of the Hungarian Academy of Sciences.

Goodey T and Goodey JB (1963) Soil and Freshwater Nematodes. New York: John Wiley & Sons.

Grasse PP (1965) Traite de Zoologie, Tome IV, Nemathelminthes (Nematodes). Paris: Masson et Cie. Fasc. 2 and 3.

GSC‐Sanger Centre (1998) Genome sequence of the Nematode Caenorhabditis elegans. A platform for investigating biology. Science 282: 2012–2018.

Levine ND (1968) Nematode Parasites of Domestic Animals and of Man. Minneapolis, MN: Burgess Publishing.

Thorne G (1961) Principles of Nematology. New York: McGraw‐Hill.

Yamaguti S (1961) Systema Helminthum, vol. III. The Nematodes of Vertebrates, Parts 1 and 2. New York: Interscience Publishers, Inc.

Zuckerman BM, Mai WF and Rohde RA (eds) (1971) Plant Parasitic Nematodes, vols. 1 and 2. New York: Academic Press.

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How to Cite close
Poinar, George(Jun 2012) Nematoda (Roundworms). In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0001593.pub3]