Müller, 1774
Description
Transparent worms, with some yellowish brown pigment anteriorly. Eyes present. Dorsal bundles beginning from VI, with 1-5 thick, curved, 135-316 µm long hair chaetae and with 1-5 87-134 µm long hair-like needle chaetae almost devoid of any nodulus. Ventral chaetae by 2-5 in II-V, 90-140 µm long, with slightly longer and thinner upper tooth; from VI on much thicker and more curved, with lower tooth longer and 2-3 times as thick as upper one. In mature individuals simple-pointed, hooked penial chaetae by 2-3. Stomachal dilatation abrupt. Length 3.5-6.5 mm, segment number in zooids 11-19, in single individuals 25-33. Can be confused with Nais pseudobtusa but differing from it in having more numerous dorsal hair and needle chaeta, of almost similar shape, as well as in possessing longer and thicker lower tooth of posterior ventral chaetae.
Crawling on substratum. Able to swim.
Distribution
Holarctic and Sino-Indian Region.
Ecology
In freshwater.
Reproduction
Mostly asexual, by paratomy (budding). Mature individuals and sexual reproduction rare or seasonal (observed in autumn, in northern Europe).
Literature
Müller, 1774: 23-24; Gervais, 1838: 17; Piguet, 1906a: 234-237, Pl. X Figs 2-4, Pl. XI Fig. 5, Pl. XII Fig. 8; Sperber, 1948: 116-118, Pl. VIII Fig. 4; Sperber, 1950: 62, Fig. 12A-C, Pl. II Fig. 2; Brinkhurst and Jamieson, 1971: 338-339, Fig. 7.7F-I; Chekanovskaya, 1981: 224-226, Fig. 97; Hrabe, 1981: 45-46, Pl. 6 Figs 7-15; Kasprzak, 1981: 119-120, Figs 320-324.