Grube, 1850
The class represents a monophyletic clade of annelids, consisting of oligochaetes and leeches.
Description
Position of testes in preovarian segments (although secondarily shifted backwards in leeches), and presence of clitellum are the diagnostic characters of the class; as well as lack of parapodia, nuchal organs, and paired palps common in most polychaete annelids. Ventral nerve cord free or within muscle layers, not sub-epidermal.
Distribution
Cosmopolitan.
Ecology
In soil, and in freshwater and marine environments; both free-living and parasitic groups known.
Reproduction
Mostly sexual, with eggs laid in cocoons. Different ways of asexual reproduction in some groups.
Literature
Brinkhurst and Jamieson, 1971: 195; Purschke et al., 2000: 166-167.