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 Major Groups | Nematoda (round worms)

Nematoda (round worms)

Roundworms are amongst the most abundant animals on earth.

Descriptive Features:

  • elongate, thin body, cylindrical in cross-section
  • posterior end tapered, anterior end usually blunt or truncate, may be tapered, most species are translucent, but some are darkly coloured
  • body enclosed in a thin cuticle, often variously sculptured or striated
  • setae may be present anteriorly
  • mouth located apically, surrounded by 3 or 6 lips, or lips absent, lips may be modified to form sucking, ripping or rasping structures
  • anus located a short distance from posterior tip
  • Total length: small animals, 0.5 - 4.0 mm (except a few at 30 cm), males typically smaller than females

    Distribution: Australia wide

    Sensitivity Rating: SIGNAL grade 3. Enoploides stewarti and Mescanthion alexandrinus were identified from the highly saline coastal Lake Alexandria, South Australia. 

    Functional Feeding Group: predator



    Lake Alexandrina, South Aus

    Ecology: Roundworms occur in all inland freshwaters from small temporary rain pools to streams and large lakes. Even within some genera and species the range of ecological conditions is broad, from thermal springs to mountain lakes. They are found in shallow areas either in shallow burrows or on or just above the substratum. Nematodes may be free living or parasitic throughout life, or have a stage in both forms. Parasitic species use either animals or plants as hosts. Free living nematodes include carnivores, omnivores, herbivores and detritivores. Locomotion is by whip like dorsoventral movements along the substratum, with the result that nematodes appear S-shaped.
    Roundworms reproduce sexually with the sexes distinct. However, in some species males are unknown and reproduction is parthenogenetic. Fertilization is internal after copulation. Most eggs hatch outside the parent, although some species do give birth to live young. Eggs are strongly resistant to desiccation. Eggs hatch to a small version of the adults. The cuticle is shed four times during the life of the worm. The life cycle of nematode species vary from two days to one year.


    Information Sources: Hodda 2004, Hodda 2001, Hodda 2000, Williams 1980, Hawking & Smith 1997, Nicholas 1993