Piguet, 1906a
Description
Transparent worms, with brown pigment anteriorly. Eyes present. Dorsal bundles beginning from VI. Hair chaetae by 1-2, quite short (90-215 µm), accompanied with 1-2 needle chaetae, 44-82 µm long, with short but distinct teeth. Ventral chaetae in II-V by 2-5, 80-136 µm long, with parallel teeth, upper tooth 1.5-2 times as long as lower one. From VI on, usually ordinary ventral chaetae, 2-5 per bundle, 65-80 long, thicker and more curved, with teeth equally long or upper tooth slightly longer and thinner. Often in VI and in some subsequent segments single giant chaetae per bundle, 80-93 µm long and up to 4.2 µm thick, with upper tooth 2-3 times as long as lower one. In mature individuals blunt penial chaetae by 2-3, about 80 µm long. On abrupt transition of oesophagus to wide midgut (stomach) in VIII, long cells projecting as brown appendage into cavity from its beginning. Length 2.5-9 mm, segment number in zooids 13-21, in single individuals 19-32. Specimens devoid of enlarged ventral chaetae can be confused with Nais variabilis. However, the latter species has a large angle between teeth of ventral chaetae in II-V; hair chaetae are more than 2.75 times as long as needles; no long cells protruding into lumen of intestinal dilatation. Specimens with enlarged ventral chaetae differ from both Nais bretscheri and Nais stolci in revealing an abrupt stomachal dilatation and in about equally long teeth of posterior crotchets. In comparison with Nais bretscheri, enlarged chaetae are less modified in Nais pardalis and begin already from VI.
Crawling on substratum. Able to swim.
Distribution
Holarctic with North Africa, Sino-Indian Region, South America.
Ecology
In freshwater.
Reproduction
Mostly asexual, by paratomy (budding). Mature individuals and sexual reproduction rare or seasonal.
Literature
Piguet, 1906a: 270-274, Pl. X Fig. 20, Pl. XII Figs 4-5, 17; Sperber, 1948: 124-126, Fig. 13N-P, Pl. VIII Figs 5-6; Sperber, 1950: 63-64, Fig. 14N-P; Brinkhurst and Jamieson, 1971: 335-336, Fig. 7.6I-L; Chekanovskaya, 1981: 232-234, Fig. 103; Hrabe, 1981: 43-44, Pl. 5 Figs. 12-19; Kasprzak, 1981: 123,127-124, Figs 365-371.