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 Major Groups | Oligochaeta (worms)

Oligochaeta (worms)

Oligochaeta is divided into two superorders, Megadrili and Microdrili. Megadriles are robust terrestrial earthworms. Microdriles are small, thin bodied aquatic worms. Identification of Oligochaeta to generic and species level usually involves internal anatomy, particularly the genital system, rather than external features. However, most families can be identified using the morphologically diverse setae that can be observed on whole mounted worms. The introduced black worm, Lumbriculus variegatus (Lumbriculidae) is a commonly cultured for aquarium fish food.

Descriptive Features:

  • elongate, cylindrical, soft body, body wall thin, translucent or opaque, colour usually brown, pinkish or red
  • body segmented, number of segments varies between species, mostly 40-200 segments (but there are extremes)
  • each segment except 1st (and sometimes a few other anterior ones) bears 4 bundles of setae, 2 dorsolateral, 2 ventrolateral, each bundle is of 1-20 setae, setae are morphologically variable and taxonomically distinct
  • suckers absent
  • Nais (Naididae) have pigmented eyespots
  • Total length: 0.5 mm - 100 mm
  • <i>Branchiura sowerbyi</> 

    Tubificidae

    <i>Chaetogaster</i> 

    Naididae

    Taxonomic Checklist:
    Capilloventridae (freshwater, marine)
    Enchytraeidae (freshwater, marine, terrrestrial)
    Haplotaxidae (freshwater, stygal) 
    Lumbriculidae (freshwater, introduced)
    Naididae (freshwater, marine, stygal)
    Phreodrilidae (almost entirely freshwater)

    Distribution: Australia wide

    Sensitivity Rating: SIGNAL grade 2. Some Tubificinae species can withstand low oxygen tensions, and are often found in large numbers in organically polluted rivers.

    Functional Feeding Group: gathering collectors

     

    Kambolgie Creek, Kakadu NP NT

    Ecology: Microdriles occur in both running and still waters including, oligotrophic lakes and streams, organically enriched wetlands, and groundwater. They are found in or on the substratum. Species with gills are found in tubes made of silt or mud with the posterior end of the worm protruding into the water. Species without gills may be found in small burrows. The smaller Naididae species swim just above the substratum with body undulations. Most other aquatic oligochaetes crawl along the substratum with peristaltic motions, side to side body movements and slight extensions and retractions of setae.
    Aquatic worms ingest large amounts of the substratum, feeding on organic material (diatoms, algal, plant) and bacteria in silt and mud. A few species of Naidinae may be carnivorous, with Chaetogaster limnaei (Naidinae) being endoparasitic in the kidney of freshwater snails. Most microdriles undergo respiratory exchange of gases at the body surface across the thin body wall. However, some Naidinae and Tubificinae species exhibit anal peristalsis where water is drawn into the posterior part of the gut for a short period for exchange of gases. Dero (Naidinae) and Branchiura (Tubificinae) have ciliated or finger-like protuberances from the body wall that act as gills.
    Oligochaetes are hermaphrodites that undergo sexual reproduction with cross fertilization (or occasionally self fertilization). A cocoon is formed from the clitellum into which fertilized eggs are deposited. Cocoons may be fastened to submerged objects or left free in the water or sediment. There are no larval stages. Naidinae species reproduce by a process of budding from a special segment. The budding segment is located towards the posterior end of the worm. During the budding process, it proliferates anteriorly to form a new hind region for the parent worm, and posteriorly to form an anterior region for the offspring. Offspring and parent may remain attached for some time and the offspring may even bud while still attached. As many as eight budded individuals (zooids) may be found together in chains.

     

    Information Sources: Pinder 2003, 2010, Pinder & Brinkhurst 1994, Williams 1980, Hawking & Smith 1997, Gooderham & Tsyrlin 2002
    Key to Families: Pinder 2010

     

     

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