Michaelsen in Pfeffer, 1890
Type species Pachydrilus georgianus Michaelsen, 1888b
Number of species about 95. Four species known from fresh waters of NWE:
Marionina argentea (Michaelsen, 1889a)
Marionina clavata Nielsen and Christensen, 1961
Marionina riparia Bretscher, 1899
Marionina southerni (Cernosvitov, 1937b)
The original genus name Marionia Michaelsen, 1889c appeared to be preoccupied, and was therefore replaced with Marionina, by the same author in the following year.
Description
Small enchytraeids, mostly white or transparent. Chaetae can be of different shape (straight or sigmoid but always with nodulus) and different number per bundle, chaetal bundles can be reduced in some segments, up to their complete lack in some species. Male pores in XII. Three pairs of pharyngeal glands. Usually no appendages on digestive tube (but rarely present on oesophagus). Blood mostly colourless, dorsal vessel reaching up to clitellar segments, seldom further backwards. Spermathecae in V, mostly connected with oesophagus, usually bearing glands on ectal duct and at ectal pore. Penial bulb present. The genus is evidently polyphyletic, without any strict common combination of characters distinguishing it from some other enchytraeid genera. Much more species are recorded from soil, or from marine habitats in NWE, but they are not included in this guide.
Burrowing in sediment.
Distribution
Cosmopolitan.
Ecology
In soil, marine littoral, and freshwater.
Reproduction
Sexual only, with eggs laid in cocoons.
Literature
Roule, 1888: 309; Michaelsen, 1888b: 65; Michaelsen, 1889c: 28; Pfeffer, 1890: 511; Ude, 1896: 23; Nielsen and Christensen, 1959: 108-110; Chekanovskaya, 1981: 391-393; Kasprzak, 1986: 141-142, Figs 397-438.