Geogenia Kinberg, 1867: 97; Perrier 1886: 876; Reynolds & Cook 1976: 52; 1993: 22; Pickford 1975: 23; Brinkhurst & Jamieson 1971: 739.
Microchaeta [partim]: Rosa 1891: 382; 1898: 1; Beddard 1895: 675.
Geogenia (Microchaeta ?): Michaelsen 1899: 428.
Geogenia (Microchaetus ?): Michaelsen 1891: 38; 1899: 428; 1900: 462.
Microchaetus: Michaelsen 1899:428 [redescription of natalensis]; [partim]: 1900: 448; 1908:40; 1913 a: 545; 1913 b: 61; 1913 c: 422; 1918: 331; Brinkhurst & Jamieson 1971: 739; Pickford 1975: 23 [partim]; Reynolds & Cook 1993: 6; Hodgson & Jamieson 1992: 112 [for pentheri]; Plisko 1995: 283; [partim]: 1991: 279; 1992: 338; 1993: 222; 1998: 250; 2002:205; 2003: 281; 2005: 105; 2006: 34. Type species: Geogenia natalensis Kinberg, 1867
Diagnosis: Holandric, testes and male funnels in 10, 11. Excretory system holoic, with V-shaped nephridial bladders. Gizzard single in segment 7. Dorsal blood vessel double in 4–9, being partly or fully separated when crossing segments, but simple after 10; in segment 8 broadly parted, in 9 enlarged, constituting a ‘cordiform’ organ. Calciferous glands not stalked, paired or encircling oesophagus, although always with dorsal or ventral vestigial grooves; in one or two segments. Spermathecae and spermathecal pores in pre-testicular, testicular or post-testicular segments. If only pre-testicular or post-testicular, then pores occur in fewer than four furrows. If in more than four furrows, pores occur anterior to testes segments, in testis and post-testicular intersegmental furrows. Two pairs of seminal vesicles; rarely only one anterior pair. Two, three or four anterior septa (4/5–8/9) variably thickened. Body length of most species 40–300 mm, some extending to 400 mm, and one species reaching 800 mm. Number of segments approximately 100–500.