Nais longidentata, Cui, Yongde, He, Xuebao, Peng, Yu & Wang, Hongzhu, 2015

Cui, Yongde, He, Xuebao, Peng, Yu & Wang, Hongzhu, 2015, Records of Naididae and Lumbriculidae (Clitellata) from Tibet, China, with description of a new species of Nais, Zootaxa 3956 (4), pp. 513-530 : 521-524

13. Nais longidentata sp. n.

( Figures 4 , 5 ; Table 2)

Holotype. IHB NMC 20110702a, mature specimen mounted in Canada balsam, and stained with borax carmine.

Type locality. ST57, N 30°47'12.6", E 90°58'43.9", Lake Namco of Tibet, ca. 4,716 m asl, lake shore substrate type coarse gravel and sand; water depth 0.3 m, water temperature 10.0°C, dissolved oxygen 7.48 mg/L, pH 10.42, conductivity 1,783 µS/cm. 2 July 2011, collected by X. B. He, Y. D. Cui.

2014).

N. longidentata N. bretscheri N. communis N. elinguis N. pardalis N. variabilis N. badia

Species sp. n. Michaelsen, 1899 Piguet, 1906 Müller, 1774 Piguet, 1906 Piguet, 1906 Peng et al., 2014 Length (mm) 4.3–5.7 3–7 1.8–12 2.2–12 2.5–7.0 3–10 4.2–9.1 Paratypes. IHB NMC 20110702b–e, 4 specimens from the type locality mounted in Canada balsam, and stained with borax carmine.

Other material. More than 50 immature specimens from ST5, ST9, ST31, ST53, ST57, preserved in 10% formalin, collected by X. B. He, Y. D. Cui.

Etymology. The specific name " longidentata ” is Latin for "with long teeth”, and refers to the needle with two long teeth.

Description. Length 3.3–7.4 mm (holotype 4.3 mm), width at VI 0.3–0.6 mm (holotype 0.5 mm), segments 34–41(holotype 34). Prostomium conical. Eyes present, body pigment absent. Pharynx in II–III. Stomach in VII– VIII, dilatation sudden in VII, no elongate cells. Clitellum inconspicuous. Coelomocytes abundant. No swimming.

Dorsal chaetae from VI onwards ( Fig. 5 F). Hairs (0)1–2 per bundle, 225–450 Μm long, with faint serration ( Fig. 5 C). Needles 1–2 per bundle, 92–112 Μm long, with two long parallel teeth (10.0–13.8 Μm long), distal tooth slightly thinner and shorter than proximal, or subequal; nodulus ca. 2/5 from distal end ( Fig. 4 D, Fig. 5 D–E). Ventral chaetae of II–V 3–4 per bundle, 78–84 Μm long, distal tooth longer and thinner than proximal, with median or slightly distal nodulus, hardly longer and thinner than the rest. Ventral chaetae from VI 2–5 per bundle, 68–78 Μm long, distal tooth slightly longer than proximal, with 1–3 fine intermediate teeth, nodulus 2/5 from distal end ( Fig. 4 A–C; Fig. 5 A–B). Penial chaetae ( Fig. 4 E) 3 per bundle, 70–112 Μm long, 4 Μm thick, simple-pointed. Male pores paired in segment VI. Spermathecal pores paired in segment V.

Clitellum in V–VI. Male genitalia paired in V–VI. Vasa deferentia ( Fig. 4 F, vd) 90–100 Μm long, 8–9 Μm wide, completely surrounded by abundant prostate gland cells ( Fig. 4 F, pr), joining the atria subapically. Atrial ampullae large and round, 120 Μm in length, 45 Μm in diameter, wall 5 Μm thick ( Fig. 4 F, at). Spermathecal ampulla pear-shaped, 90 Μm long, 50 Μm wide, with distinct duct 60–70 Μm long, 9–10 Μm wide ( Fig. 4 F, sp).

Distribution. Known only from Lake Nam Co and Lake Yamzho Yumco of Tibet.

Remarks. Considering the characters such as the presence of eyes, coelomocytes abundant, dorsal chaetae from VI with hairs and double-pronged needles, ventral chaetae of II–V longer and thinner than the rest, pharynx in II–III, stomach beginning in VII, spermathecae with distinct ducts, vasa deferentia with prostate gland cells joining the atria subapically, atria without prostate glands, penial chaetae present with a simple hook, we think that the new species fits the definition of Nais Müller, 1773 ( Sperber 1948; Brinkhurst & Jamieson 1971; Hrabě 1979; Timm 1999; Envall et al. 2012).

About 31 species have been described in Nais , and ten species are distributed in China ( Sperber 1948; Liang 1964; Brinkhurst & Jamieson 1971; Semernoy 2004; Envall et al. 2012; Peng et al. 2014). N. longidentata sp. n. is distinguished from congeners in having long and parallel needle teeth, faintly serrated hairs, and pectinate ventral chaetae with 1–2 intermediate teeth.

Comparing N. longidentata sp. n. with allied species ( Table 2), the new species is similar to N. elinguis by the long and parallel needle teeth. However, the needles of the new species are longer than those of N. elinguis (10.0– 13.8 Μm vs. 3.1–4.6 Μm). N. badia Peng et al., 2014 resembles the new species in serrate hairs and pectinate ventral chaetae, but its large area of reddish brown pigment in I–VIII, wave-like body movements, and vasa deferentia with prostate gland cells only on their posterior parts are significantly different from N. longidentata sp. n.. Among further similar species, N. bretscheri Michaelsen, 1899 differs from the new species in giant chaetae in some anterior ventral segments; N. communis Piguet, 1906 differs in the thick prostate gland cells only on their posterior parts; N. variabilis Piguet, 1906 and N. pardalis Piguet, 1906 swim with spiral body movements and their stomach has elongate cells. In all these species the needle teeth are considerably shorter than in N. longidentata sp. n.

Figures

FIGURE 4. Nais longidentata n. sp. A – C. Ventral chaetae (III, VI, posterior, respectively). D. Needles. E. Penial chaetae. F. Lateral view of sexual organs in segments V – VI. Scale bar: A – D 20 Μm; E 50 µm, F 100 µm.

FIGURE 5. SEM (A – E) and optical microscope (F) micrographs of Nais longidentata n. sp. A – B. Ventral chaetae in IX (A) and XIII (B). C. Hair in VII. D – E. Needles in X (D) and a posterior segment (E). F. Lateral view of anterior body. Scale bars: A, B, D 20 µm, C 5 µm, E 10 µm.