Standard Article

Nematoda (Roundworms)

  1. George Poinar Jr

Published Online: 15 JUN 2012

DOI: 10.1002/9780470015902.a0001593.pub3



How to Cite

Poinar, G. 2012. Nematoda (Roundworms). eLS. .

Author Information

  1. Oregon State University, Corvallis, Oregon, USA

Publication History

  1. Published Online: 15 JUN 2012


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.


  • nematodes;
  • roundworms;
  • plant parasites;
  • metazoans;
  • invertebrates