(Gruithuisen, 1828)
Description
Small and stout, transparent worm, usually occurring as a chain of several zooids. Five anterior segments fused forming head and containing muscular pharynx. Prostomium conspicuous, conical in preserved worms but oval and with sensory hairs in living ones. Chaetae in ventral bundles only (seldom atavistic forms with vestigial dorsal chaetae can occur), absent from III-V. In II, chaetae 4-8 per bundle, 70-112 µm long. From VI on, chaetae 3-7 per bundle, 42-81 µm long. Penial chaetae 2-3 per bundle, 70 µm long. Length 1-5 mm, segment number in zooids 8, in single worms 10-18. Easily distinguishable from other congeners in having distinct prostomium. In the closely related, probably synonymous, Chaetogaster palustris Pointner, 1911, extremely long sensory hairs occur both on prostomium and body segments. Pseudochaetogaster longemeri Lafont, 1981, bearing dorsal bundles with 2 bifid chaetae from VI on, may be an atavistic form of Chaetogaster diastrophus.
Crawling on substratum.
Distribution
Almost cosmopolitan. Both Chaetogaster palustris and Pseudochaetogaster longemeri are recorded from Western Europe; equivalents of the latter but named as Chaetogaster diastrophus, known also from the Great Lakes of North America.
Ecology
In various freshwater bodies, living on water plants and bottom sediment. Common. Feeding on algae and minute animals.
Reproduction
Paratomy (budding). Sexually mature individuals rare.
Literature
Gruithuisen, 1828: 416-420, Pl. XXV Figs 7-9; Sperber, 1948: 59-62, Figs 3C, 6, 7A,B,G, Pl. I fig. 1; Sperber, 1950: 52, Figs 3A,B; Brinkhurst and Jamieson, 1971: 307-308, Fig. 7.1A-E; Chekanovskaya, 1981: 256-257, Figs 117-118; Hrabe, 1981: 32, Pl. 2 Figs 1-4, 13; Kasprzak, 1981: 93, Figs 169-173. For C. palustris: Pointner, 1911: 629-630, Pl. XXVIII Figs 2-3; Sperber, 1948: 63. For Pseudochaetogaster longemeri: Lafont, 1981b: 27-32, Figs 1-4.