Piguet, 1906a
Description
Transparent worms but usually with brown pigment in anterior segments. Eyes usually present. Oesophagus gradually dilating to midgut. Dorsal bundles beginning from VI, consisting of 1-2 hair chaetae, 90-270 µm long, and 1-2 needle chaetae, 40-82 µm long, with distinct diverging teeth. Ventral chaetae in II by 2-7, 40-93 µm long, with upper tooth longer and thinner; from VI on by 2-6, 54-91 µm long, only slightly thicker and more curved than anterior chaetae, with gradually levelling tooth length. In mature individuals penial chaetae by 2-3, either hooked or with reduced upper tooth. Length 1.5-12 mm, segment number in zooids 10-21, in single individuals 12-32. Can be confused with Nais variabilis when preserved, but has usually shorter hair chaetae, larger teeth in needle chaetae, smaller difference between anterior and posterior ventral crotchets, and gradual dilatation of stomach. Nais variabilis can swim but Nais communis can not.
Crawling on substratum, unable to swim.
Distribution
Cosmopolitan.
Ecology
In freshwater.
Reproduction
Mostly asexual, by paratomy (budding). Mature individuals and sexual reproduction rare or seasonal.
Literature
Piguet, 1906a: 247-253, Pl. X Fig. 9, Pl. XI Figs 14-17, 19, Pl. XII Fig. 11; Sperber, 1948: 102-107, Pl. VII Fig. 1; Sperber, 1950: 60, Fig. 10; Brinkhurst and Jamieson, 1971: 220-332, Fig. 7.5E-H; Chekanovskaya, 1981: 229-230, Fig. 100; Hrabe, 1981: 40-41, Pl. 4 Figs 6-10; Kasprzak, 1981: 129, Figs 381-384.