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A class of the phylum Annelida including worms such as the earthworms. There are 21 families with over 3000 species. These animals exhibit both external and internal segmentation. They usually possess setae which are not borne on parapodia. Oligochaetes are hermaphroditic. The gonads are few in number and situated in the anterior part of the body, the male gonads being anterior to the female gonads. The gametes are discharged through special ducts, the oviducts and sperm ducts. A clitellum is present at maturity. There is no larval stage during development.

The oligochaetes are primarily fresh-water and burrowing terrestrial animals. A few are marine and several species occur in the intertidal zone.

Oligochaetes are cylindrical, elongated animals with the anterior mouth usually overhung by a fleshy lobe, the prostomium, and the anus terminal. The body plan is that of a tube within a tube. Externally, the segments are marked by furrows. The setae or bristles are borne on most segments. Other external features are the pores of the reproductive systems opening on certain segments, the openings of the nephridia, and in many earthworms dorsal pores which open externally from the coelom. Some aquatic species have extensions of the posterior part of the body which function as gills.

The oligochaetes have been used in studies of physiology, regeneration, and metabolic gradients. Some aquatic forms are important in studies of stream pollution as indicators of organic contamination. Earthworms are important in turning over the soil and reducing vegetable material into humus. It is likely that fertile soil furnishes a suitable habitat for earthworms, rather than being a result of their activity. See Annelida



oligochaetes, a class of annelid worms.

The body length of the Oligochaeta varies from fractions of a millimeter to 2.5 m (some tropical earthworms). There is a secondary body cavity (coelom). Metamerism of the body is well expressed; the body consists of a varying number of segments (from 5-7 up to 600). All segments, except the mouth segment, as a rule have chaeta (bristles) in bundles (two dorsal and two ventral on each segment) of from two to several dozens per bundle. Oligochaeta are hermaphrodites; the sex organs are concentrated in a few segments of the body. In the representatives of certain families there is also asexual reproduction; in some species parthenogenesis takes place. The eggs develop without metamorphosis.

There are about 3,000 species of Oligochaeta, including about 2,000 soil species; the rest live in freshwater and a few species live in the sea. In the USSR there are over 200 aquatic and about 100 soil species. The majority of Oligochaeta feed on plant detritus, which they ingest with the soil; some species are predators; the representatives of one family are ectoparasites of river crayfish (crayfish “leeches”)- Oligochaeta play an important role in the cycle of matter in water and soil, determining the rate of silt formation and mineralization of sediments in freshwater and influencing soil structure and humus formation. Oligochaeta are very important in the processes of self-purification of contaminated waters; they serve as food for fish.


Rukovodstvo po zoologii, vol. 2. Edited by L. A. Zenkevich. Moscow-Leningrad, 1940.
Chekanovskaia. O. V. Dozhdevye chervi i pochvoobrazovanie. Moscow-Leningrad, 1960.
Chekanovskaia, O. V. Vodnye maloshchetinkovye chervi fauny SSSR. Moscow-Leningrad, 1962.



(invertebrate zoology)
A class of the phylum Annelida including worms that exhibit both external and internal segmentation, and setae which are not borne on parapodia.
References in periodicals archive ?
High densities of Oligochaeta and Chironomidae are indicative of high levels of organic matter (Lang, 1998; Hepp and Santos, 2009), as these benthic invertebrates are more tolerant to pollution (Bubinas and Jagminiene, 2001).
During the study in the Anzali International Wetland from August 2012 to June 2013, 11 species and one genus of Oligochaeta were found.
2006), macroinvertebrate samples from sites below dams had relatively more Chironomidae larvae and Oligochaeta and fewer of the more sensitive taxa, Plecoptera, Ephemeroptera and Trichoptera.
The present study indicates that this type specimen (GNM Oligochaeta 16), should now be known as Tritogenia zuluensis (Beddard, 1907).
1974, "The distribution of Oligochaeta in Saginaw Bay lake Huron" Limnology and Oceanography, 12, 137-143.
ORDENES Riqueza total Oligochaeta 1 Decapoda 3 Coleoptera 18 Diptera 13 Ephemeroptera 16 Hemiptera 12 Lepidoptera 2 Megaloptera 1 Odonata 13 Orthoptera 2 Plecoptera 1 Trichoptera 22 Unionoida 1 Basomatophora 7 Total 112 Tabla 5.
For the Opilionida, Cryptostigmata and Psocoptera there was a positive correlation between altitude and density while the density of Oligochaeta, Araneae and Hemiptera was negatively correlated with altitude.
Este articulo describe la posibilidad de usar gusanos Oligochaeta para sanear los sedimentos bentoncos encontrados en petroleo e hidrocarburos.
Taxa Feeding Number of Number of Life Guild individuals bromeliads cycle with taxa stage Mollusca Gastropoda, Bulimulidae Hb 3 3 A Gastropoda, Subulinidae Hb 1 1 A Annellida Oligochaeta Dt 48 20 A+I Chelicerata Aranae, Lycosidae Pr 13 8 A Aranae, Argiopidae, Argiope argentat Pr 1 1 A Aranae, Theraphosidae, Pachistopelma rufonigrum Pr 14 13 A Aranae, Salticidae Pr 6 5 A+I Aranae, Theraphosidae sp 2 Pr 2 2 A Pseudoscorpiones Pr 1 1 A Scorpiones, Bothriuridae, Bothriurus asper Pr 1 1 A Scorpiones, Buthidae Tityus neglectus Pr 4 4 A Myriapoda Chilopoda, Scolopendridae Pr 8 7 A Diplopoda , Spirobolida Pr 25 15 A+I Hexapoda, Insecta Blattariae, Blattidae sp.
O represamento que ocorreu em P4 teve influencia direta sobre a densidade e composicao de especies, pois Chironomidae e Oligochaeta apresentaram aumento de suas populacoes e tornaram-se dominantes dentro da comunidade de invertebrados bentonicos.
3) Percent Oligochaeta and Chironomidae (% OC)--A high percentage of these taxa can indicate low dissolved oxygen concentration (DO), elevated sedimentation rates, or high levels of suspended solids.
La biomasa es mas alta en Pajonal (51%) donde Oligochaeta aporta el 68% del peso.