Oligochaeta
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| Oligochaeta | ||||||||
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| Missing image Earth-worm_1.jpg Image: Earth-worm_1.jpg Earthworm (Lumbricus terrestris) | ||||||||
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| Arhynchobdellida Haplotaxida Rhynchobdellida |
The Oligochaeta or "few-bristled" worms (singular Oligochaete, IPA /ˈɒlɪgoʊˌkit/) are well-segmented Annelids, most with a spacious coelom that is used as a hydroskeleton. Their setae (chaetae) or "bristles" are generally few in number and they lack the parapodia of the polychaeta. They have external fertilization, but copulate and store sperm in a receptacle called a spermatheca. Like the leeches, they have a clitellum which secretes a "cocoon" into which both eggs and sperm are deposited and which acts as an incubator for the embryonic worms. They lack a trochophore larval stage.
This taxon contains mainly freshwater and semi-terrestrial forms, including the earthworms (some of which are fully terrestrial), the tubificids, pot worms, ice worms and many interstitial marine worms. Most are detritus feeders. Some genera are predaceous (Agriodrilus and Phagodrilus).