Michaelsen, 1899
Description
Transparent worms, often with heavily pigmented anterior end. Eyes usually present. Dorsal bundles beginning from VI. Hair chaetae single, short (81-172 µm); beside them, 1-2 needle chaetae, 49-75 µm long, with quite long (up to 4.5 µm) parallel teeth. Ventral chaetae in II-V by 2-7, 70-118 µm long, with long parallel teeth, upper tooth twice as long as lower one. Giant chaetae beginning from VII, sometimes reaching to XIII, 1-2 per bundle, 78-127 µm long and 3-8 µm thick, straight, with very short, sometimes cleft or reduced, lower tooth. In VI and behind giant chaetae, ventral chaetae by 2-5, 57-90 µm long, thicker and more curved than in II-V, with upper tooth twice as long. In mature individuals hooked penial chaetae by 2. Stomachal dilatation gradual. Length 3-7 mm, segment number in zooids 13-22, in single individuals 17-35. The only species of Nais that reveal sometimes similar, although less modified, giant chaetae, are Nais pardalis and Nais stolci. However, giant chaetae begin already from VI in these species but always from VII in Nais bretscheri.
Crawling on substratum.
Distribution
Holarctic, China and Japan, South America.
Ecology
In freshwater, mostly on hard sediment.
Reproduction
Mostly asexual, by paratomy (budding). Mature individuals and sexual reproduction rare or seasonal.
Literature
Michaelsen, 1899: 121-122; Sperber, 1948: 120-123, Fig. 13A-M; Sperber, 1950: 63, Fig. 14A-M; Brinkhurst and Jamieson, 1971: 334-335, Fig. 7.6B-H; Chekanovskaya, 1981: 235-237, Fig. 105; Hrabe, 1981: 42-43, Pl. 5 Figs 1-11; Kasprzak, 1981: 123-125, Figs 337-354.