Chaetogaster diaphanus Gruithuisen 1828

1. Chaetogaster diaphanus (Gruithuisen, 1828)

(Figure 2)

Chaetogaster diaphanus (Gruithuisen). Chen 1940: 29–31; Liang 1964: 643 –644, 1979: 274; Wang 2002: 80; Timm & Všivkova 2007: 26; Cui 2008: 60.

Material examined. Lhasa River: ST12, 1 specimen (spm). Niyang River: ST30, 1 spm; ST31, 1 spm; ST32, 1 spm. Lalu Wetland: ST62, 3 spms.

Description of new material. Length 2.4–5.0 mm, width 0.8–1.0 mm, segments 10–15. No eyes. Prostomium inconspicuous. Pharynx developed, with thick muscle layer, pharyngeal glands in II–IV. Oesophagus narrow in IV. Stomach in V–VI, and dilatation sudden in V. Stomachal plexus forming transverse ducts only anteriorly. No dorsal chaetae. Ventral chaetae (Fig. 2 A–C) of II 9 per bundle, 225–238 Μm long, about 4.5 Μm thick, upper prong longer than lower, with distal or median nodulus; from III on 7–11 per bundle, 174–221 Μm long, about 3 Μm thick, upper prong curved, longer and thinner than lower, with almost median nodulus. Penial chaetae (Fig. 2 D–F; Fig. 2 G, pc) 7 per bundle, about 112 Μm long, 4 Μm thick, simple-pointed or with 2–3 short fine teeth, with distal nodulus. Male pores paired in line with ventral chaetae, middle VI. Spermathecal pore paired in line with ventral chaeta, anterior to mid-V. Clitellum in 1/ 2V–VI. Male genitalia paired in V–VI. Male funnel (Fig. 2 G, sf) cup-shaped, 80 Μm long, 84 Μm wide, with 12.5 Μm thick wall. Vasa deferentia (Fig. 2 G, vd) short, 28 Μm wide, joining atria apically. Atrial ampulla (Fig. 2 G, at) large, round, 168 Μm long, 144 Μm in diameter, 17.5–22.5 Μm thick wall, with sperm masses (Fig. 2 G, sm) in lumina. Spermathecal ampulla (Fig. 2 G, sa) pear-shaped, about 75 Μm long, 87 Μm wide, with 10 Μm thick wall, ducts very short.

Remarks. This species is widely distributed in China (Wang & Cui 2007) and has also been recorded from Tibet by Stephenson (1909). The new material conforms to previous descriptions in most aspects except the body width and the number of penial chaetae (Chen 1940; Sperber 1948; Timm 1999). The new specimens are thicker than previously collected material from China (Liang 1964), but within the range given by Timm (2009) for European specimens. In our specimens there are usually 7 penial chaetae per bundle, whereas in previous descriptions there are only 3–5 per bundle (Chen 1940; Sperber 1948; Liang 1964; Brinkhurst & Jamieson 1971; Timm 1999).