Oligochaeta (phylum Annelida) A class of worms that have very well-developed metameric segmentation. The segments have only a few chaetae (hence the name), but parapodia are not present. They are all hermaphrodites; asexual reproduction is predominant in aquatic forms. Eyes and tentacles are absent. A few marine forms occur but most are freshwater or terrestrial. There are 15 families, and the class is first recorded from the Upper Ordovician.

Oligochaeta (phylum Annelida) Class of annelid worms which possess very well-developed metameric segmentation. The segments have bristles, but parapodia (movable, paired lateral appendages) are not present. They are all hermaphrodites; asexual reproduction is predominant in aquatic forms. Eyes and tentacles are absent. A few marine forms occur but most are freshwater or terrestrial. There are 15 families, and the class is first recorded from the Upper Ordovician.

earth·worm / ˈər[unvoicedth]ˌwərm/ • n. a burrowing annelid (Lumbricus, Allolobophora, and other genera, family Lumbricidae) that lives in the soil.

Oligochaeta A class of hermaphrodite annelid worms that bear only a few bristles (chaetae). Oligochaetes are very abundant in freshwater and terrestrial habitats. The most familiar members of the class are the earthworm (Lumbricus) and the freshwater bloodworm (Tubifex).

earthworm Annelid with a cylindrical, segmented body and tiny bristles. Most worms are red, pink or brown, and live in moist soil. Their burrowing loosens and aerates the soil, helping to make it fertile. Length: 5cm–33m (2in–11ft). There are several hundred species. Class Oligochaeta; genus Lumbricus.