Tubifex gracilentus, Cui, Yongde, 2017

Cui, Yongde, 2017, Four species of Tubifex Lamarck (Annelida: Oligochaeta: Naididae) from Tibet, China, Zootaxa 4320 (2), pp. 366-378 : 369-371

Tubifex gracilentus n. sp.

( Figs. 4–6 )

Holotype. IHB XZ20150511 a, mature specimen, stained and whole-mounted in Canada balsam.

Type locality. Juemu River (29°39'23″N, 94°17′12″E), southeast Tibet of China, ca. 3,290 m asl. Sediment silt. Water depth 40–60 cm, water temperature 6.4°C, pH 6.2, dissolved oxygen 8.8 mg /L, and conductivity 12.3 µs/cm. Collected on 11 May 2015 by the authors.

Paratype. IHB XZ20150511 b, 1 mature specimen, stained and whole-mounted in Canada balsam, from the type locality.

Other material. 1 specimen for SEM, from the type locality; 1 mature specimen whole-mounted in Canada balsam, from Trigu Co ( Co means lake in Tibet).

Etymology. The epithet “ gracilentus ” is Latin for “slender and thin”, and refers to the thin and long penial sheath of this species.

Description. Length 6.4–6.7 mm (Holotype: 6.7 mm), width at genital segments X–XI 0.5–0.6 mm (holotype: 0.6 mm). Segments 32–34 (holotype: 32). Prostomium obtuse or conical ( Fig. 4A ). Clitellum inconspicuous. No coelomocytes.

Dorsal chaetae (0) 1–2 hairs and 1–4 bifids per bundle. Hairs smooth anteriorly ( Fig. 4B ), serrate posteriorly ( Fig. 4C ), 120–300 µm long, 2–3 µm thick. Dorsal bifids pectinate, 50–100 µm long, 1.5–2.5 µm thick, upper and lower tooth subequal, 6–8 µm long, with 2–3 (4) fine intermediate teeth, nodulus distal ( Figs. 4D , 5D ). Ventral chaetae bifid, (2) 4–6 per bundle anteriorly, 2–3 per bundle posteriorly, 60–160 µm long, 2–3 µm thick, upper tooth twice as long as lower (4 µm/2 µm), with (0) 1–2 fine intermediate teeth, nodulus distal ( Figs. 4E,F , 5A–C ). Ventral chaetae in X–XI present, unmodified. Male pores ( Figs. 5G , 6C : mp) paired in line with ventral chaetae in anterior of X. Spermathecal pores ( Fig. 5E : spp) paired in line with ventral chaetae, middle to posterior of XI.

Chloragogen cells from VI onwards. Male genitalia paired in X–XII. Sperm funnel cup-shaped, 30–40 µm long, 40–60 µm wide ( Fig. 5G, H : sf). Vas deferens long and irregularly coiled, 1800–2000 µm long, at least 3 times as long as atrium, anteriorly 14–16 µm wide, posteriorly 28 µm wide, ciliated throughout and entering atrium apically ( Figs. 5G, H , 6A : vd). Atrium spindle-shaped, 560–640 µm long, maximally 80–100 µm wide ( Figs. 5G, H , 6A : at). Ejaculatory duct 100–120 µm long, 20–32 µm wide, entering muscular bulb ( Fig. 5G, H , 6A : ed; Fig. 5G : mb). Prostate gland large, attached to ental portion of atrium, 120–140 µm long, 80–100 µm wide ( Fig. 5G, H , 6A : pr). Penis inconspicuous, surrounded by cuticular, symmetrical and funnel-shaped penial sheath. Penial sheath extremely thin, long and sinuous, 32–36 µm wide at ental end, 3–5 µm wide at thin and prolonged ectal portions, 520–540 µm long, length to width ratio nearly 15–16 ( Figs. 5G, H , 6B : ps). Testes paired in X, immediately behind septum 9/10. Ovaries paired in XI, immediately behind septum 10/11. Spermathecae paired in X, ampullae oblong, 200–280 µm long, 140–250 µm wide; duct 100–120 µm long, 24–28 µm wide; sperm random in lumina, no spermatozeugmata ( Figs. 5E , 6C : sp).

Remarks. The main identification characteristics of long and winding vas deferens divided into thin and thick sections, long atrium gradually tapering towards distal portion, large prostate gland and elongate penial sheath suggest that the present species belongs to the genus Tubifex ( Brinkhurst & Jamieson 1971; Holmquist 1985; Juget et al. 2006). Tubifex tubifex (Müller, 1774) resembles this species in pectinate dorsal chaetae, long and winding vas deferens divided into thin and thick sections, large prostates, and in atria with a long ejaculatory duct, but differs from it in a cylindrical penis covered with a short and tub-shaped cuticle ring. Furthermore, spermathecae are absent, or present with spermatozeugmata, or present with empty ampullae. T. gracilentus n. sp. is easily distinguished from its congeners by the extremely thin and long funnel-shaped penial sheath (Table 2).

Distribution and habitat. Known from the type locality, Cuomujiri Lake and Trigu Co. Freshwater.

Figures

FIGURE 4. Tubifex gracilentus n. sp., SEM micrographs. A. Lateral view of anterior body. B. Hair in IV. C. Hair in XII. D. Dorsal pectinate chaeta in XII. E. Ventral chaeta in IV. F. Ventral chaeta in XIII. Scale bars: A. 500 µm; B – F. 20 µm.

FIGURE 5. Tubifex gracilentus n. sp. A. Ventral chaeta in II. B. Ventral chaeta in IV. C. Ventral chaeta in a posterior segment. D. Distal tip of dorsal pectinate chaeta in VIII. E. Spermatheca. F. Penial sheath. G. Male genitalia in X – XII, dorsal view. H. Male genitalia in X – XII, lateral view. Scale bars: A – D. 20 µm; E – H. 100 µm.

FIGURE 6. Tubifex gracilentus n. sp., micrographs from live worms. A. Ventral view of male genitalia in X – XII. B. Penial sheath and muscular bulb. C. Spermatheca and male pore.