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Animal Phyla/Nematoda

< Animal Phyla
Mermis nigrescens beentree, a nematode worm.
  • Nematoda
  • Name Meaning: Thread like
  • English Common Name: Round worms, Nematodes
  • Major distinguishing characteristics: Round cross section, keratin, cuticle
  • Approximate number of species described: 80 000 - 1 million

Natural History

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Nematodes live in almost every environment. About half of known species are parasitic, about 35 species in humans.

About 90% of the animals found on the ocean floor are Nematodes. They have been found in the deepest gold mines in South Africa.

Taxonomy

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There are at least four classes, but little is known about many nematodes, so this is subject to revision.

  • Chromadorea
  • Enoplea
  • Secernentea
  • Dorylaimea

Over 2200 genera are recognized in over 250 families. New species are regularly being described.

Anatomy

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Nematodes are worms ranging in length from 0.1 millimeter to 1 meter (3 feet).

They have a tubular digestive system with a mouth and an anus. The mouth may have three or six "lips", and may have teeth.

The body is bilaterally symmetrical, but the distinct head is radially symmetrical.

The Fossil Record

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Nematodes are soft bodied and most are extremely small making fossilization problematic. However, fossils from Cambrian China have been found, suggesting they existed in the Precambrian.

Quiz

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References and Further Reading

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