Piguet, 1906a
Description
Transparent worms, sometimes with pigment. Eyes present. Dorsal bundles beginning from VI, with 1-2 hair chaetae, 190-270 µm long, and with 1-2 obtusely simple-pointed needle chaetae, 60-80 µm long. In ventral chaetae of II-V lower tooth diverging from upper one (and from the longitudinal axis of chaeta) almost at a right angle. In needle chaetae nodulus at about 1/3 from distal end. Ventral chaetae by 2-6, 73-120 µm long, their teeth equally thick but upper one 1.6-2 times as long as lower one. From VI on, ventral chaetae by 2-5, 63-95 µm long, thicker and more curved than anterior ones, with teeth equally long or upper tooth slightly longer but always 2-3 times as thin. In mature individuals hooked penial chaetae by 2-3. Stomachal dilatation sudden. Length 4-9 mm, segment number in zooids 14-22, in single individuals 17-40. Can be confused with Nais variabilis that has very fine, sometimes hardly distinguishable teeth in needle chaetae. Similar obtuse needle chaetae of Nais alpina and Nais behningi reveal more distal nodulus, while teeth are parallel in anterior ventral crotchets of those species, and the upper tooth is considerably longer in their posterior crotchets.
Crawling on substratum. Able to swim.
Distribution
Almost cosmopolitan
Ecology
In freshwater.
Reproduction
Mostly asexual, by paratomy (budding). Mature individuals and sexual reproduction rare or seasonal.
Literature
Piguet, 1906a: 260-266, Pl. XI Figs 22, 24, Pl. XII Figs 1-3, 14; Sperber, 1948: 110-112, Figs 11A-C, 26E, Pl. VII Figs 3-5; Sperber, 1950: 61, Fig. 11A-C; Brinkhurst and Jamieson, 1971: 333-334, Figs 7.5M-O, 7.6A; Chekanovskaya, 1981: 226-227, Fig. 98; Hrabe, 1981: 47, Pl. 6 Fig. 20, Pl. 7 Figs 1-6; Kasprzak, 1981: 122, Figs 332-336.