Oligochaete are annelid worms and have a global distribution. These segmented thread-like worms vary in size from less than 1 mm to over 1 m, but marine oligochaetes rarely exceed several centimeters in length. Unlike their close relatives the polychaetes, they show limited diversity of body form.

They live buried in soft sediment, crawling and eating the way through the organic deposits. Marine oligochaetes are rather resistant to unfavorable conditions such as high contaminant load, low oxygen concentrations, eutophic conditions and
high silt concentrations.

The body of oligochaetes is partitioned into repeating cylindrical segments. The number of segments ranges from less than 10 to over 100 with a head (prostomium) in front of the first segment. Each segment bears 4 pair of small spines or "chaeta" which they can extend to help them grip sediments while crawling, and a complete set of most body organs, with blood vessels and a nerve cord running the entire body length. A heart occurs stretched across several of the forward segments. Adults have a clitellum, a thickened skin of glandular skin on several segments, which places oligochaetes in the class ‘Clitellata’ of the Annelids. Oligochaetes can regrow a major part of their rear body when it gets eaten by a predator.

There are over 5,000 species worldwide, showing higher diversity in freshwaters, with about 800 species in brachish and marine waters. An estimated 39 species live in Arctic waters.

Page Author: Bodil Bluhm
Created: Sept 20, 2010

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