Piguet, 1906a
Description
Transparent worms, sometimes anteriorly pigmented. Dorsal bundles beginning from VI, with 1-2 hair chaetae, 115-643 µm long, and 1-2 finely bifid needle chaetae, 42-86 µm long. Ventral chaetae by 2-7, in II-V 60-135 µm long, with upper tooth longer and thinner; basal portions of teeth diverging right off at an acute angle; lower tooth forming a right angle with the longitudinal axis of chaeta. From VI on, ventral chaetae shorter (60-105 µm), much thicker and more curved, with teeth of about equal length, or upper one slightly longer but always thinner. In mature individuals hooked penial chaetae by 3-4. Stomachal dilatation abrupt. Length 4-10 mm, segment number in zooids 12-21, in single individuals 18-38. Highly variable species but some former variants were later on defined as separate species (Nais simplex, Nais pardalis, Nais christinae). Can be confused with Nais simplex if bifidity of needle chaetae remains unnoticed; with Nais christinae and Nais pardalis, which have parallel teeth in their anterior ventral chaetae; and, particularly, with Nais communis. However, the last species usually reveals shorter hair chaetae, larger teeth in needle chaetae, smaller difference between anterior and posterior ventral crotchets and gradual stomachal dilatation.
Crawling on substratum. Able to swim (unlike Nais communis).
Distribution
Cosmopolitan.
Ecology
In freshwater.
Reproduction
Mostly asexual, by paratomy (budding). Mature individuals and sexual reproduction rare or seasonal.
Literature
Piguet, 1906a: 253-260, Pl. X Figs 10-18, Pl. XI Figs 18, 20-21, 23, Pl. XII Figs 12-13; Sperber, 1948: 107-110, Pl. VI Fig. 3, Pl. VII Fig. 2; Sperber, 1950: 60, Pl. I Fig. 8; Brinkhurst and Jamieson, 1971: 332-333, Figs 7.5T-L, 7.8N-Q; Chekanovskaya, 1981: 231-232, Fig. 102; Hrabe, 1981: 40, Pl. 4 Figs 11-15; Kasprzak, 1981: 128, Figs 372-374.