Brinkhurst, 1971 in Brinkhurst and Jamieson, 1971
Type family Lumbriculidae Vejdovsky, 1884b
Number of species about 170. The families Lumbriculidae and Dorydrilidae with ten genera and 34 species known from NWE.
Description
Small to large aquatic oligochaetes. Chaetae two per bundle (very seldom absent), sigmoid with nodulus, either simple-pointed or with shorter upper tooth. Male ducts prosoporous, with the single or the second pair of testes in atrial segment, or plesioporous in case the second pair of testes is reduced. One pair of atria (seldom two or more pairs in neighbouring segments, or one unpaired atrium) most often in X. Ovaries usually in the first postatrial segment; spermathecae, in variable numbers, can lie both in preatrial and postatrial segments, seldom in atrial segment. Clitellum covers several segments, among them the one with male pores. The order is hard to define, since it has no synapomorphies. Dorydrilidae can be included only with the postulate that their plesioporous male ducts (comparable with those in Tubificida and Enchytraeida) have developed secondarily from the prosoporous type, characteristic of Lumbriculidae, by full reduction of the second pair of testes and vasa deferentia. In case this assumption were erroneous, the order would be polyphyletic. On the other hand, it would also be paraphyletic if the prosoporous but otherwise highly derived Branchiobdellidae and Hirudinea were not included. Setting aside the problem of prosopority, the structure of the male ducts is rather similar in Lumbriculida and Tubificida, while simple sigmoid and always paired chaetae of Lumbriculida are very similar to those of Haplotaxida and Lumbricida.
Burrowing in sediment. Some species able to swim short distances.
Distribution
Holarctic, particularly diverse in Lake Baikal; single introductions to the Southern Hemisphere.
Ecology
In freshwater, mostly preferring cool oxygen-rich habitats, including groundwater.
Reproduction
Mostly sexual only, with eggs laid in cocoons. Architomy (fragmentation) in some species.
Literature
Michaelsen, 1930: 416-418; Cook, 1968: 273-289; Brinkhurst and Jamieson, 1971: 190, 195.