Rheotanytarsus cangshanensis Lin & Yao, 2024

Rheotanytarsus cangshanensis Lin & Yao , sp. nov.

( Figs 1B, 3)

Material examined. Holotype ♂ ( SHOU: XL1194 ), China, Yunnan, Dali, Cangshan Mountain , Qingbi Stream , Qinglong Pond , 25.647531°N, 100.142625°E, elev. 2558 m, 20.V.2018, light trap, leg. X.L. Lin. Paratypes. 2♂ ( SHOU: XL1197 , XL1209 ), same data as holotype GoogleMaps .

Etymology. The specific name refers to the type locality, Cangshan Mountain.

Diagnosis. The adult males can be distinguished from other species of acerbus group by the following combination: AR 0.32–0.34; anal tergite bands of V-type, well developed and separated; the tergite IX with eight strong setae along the posterior margin; anal point triangular, with rounded apex, and anal crests of Y-type, basally developed and apically opened; superior volsella oval, and ovate; the stem of median volsella straight, with petal-shaped lamellae on apex.

Description. Adult males (n = 3, except stated). TL 2.65–2.79, 2.74 mm. WL 1.72–1.75, 1.74 mm. TL/WL 1.54–1.59, 1.57. WL/length of profemur 2.08–2.10, 2.09.

Coloration. Thorax yellowish brown except postnotum with a brown area, abdomen pale yellow except apical 1/3 yellow and hypopygium light brown, fore legs brown except tarsomeres 2–5 dark brown, mid and hind legs with pale yellow femur and rest pale brown.

Head. Ultimate flagellomere 196–207, 201 μm long. AR 0.32–0.34, 0.33. Temporal setae 9–10, 10. Clypeus with 15– 17, 16 setae. Tentorium 97–109, 103 μm long, 28–31, 30 μm wide. Palpomere lengths (in μm): 35–45, 40; 29–33, 31; 127– 143, 133; 124–128, 125; 228–288, 258; Pm5/ Pm3 1.80–2.01, 1.94. Third palpomere with 2 sensilla clavata distally.

Thorax. Ac 9–11, 10; Dc 10–11, 10; Pa 1, Scts 8–10, 9. Halteres with 7–8, 7 setae.

Wing ( Fig. 1B). VR 1.43–1.46, 1.45. Brachiolum with one seta, Sc with 1–2, 1 setae, R 18–20, 19 setae, R 1 28–32, 30 setae, R 4+5 60–67, 63 setae, RM with one seta, M 1+2 61–68, 65 setae, M 3+4 40–43, 41 setae, false vein 74–87, 77 setae, Cu 18–22, 20 setae, Cu 1 24–25, 24 setae, PCu 50–52, 51 setae, An 33–35, 35 setae, remaining veins bare. Cell r 4+5 about 250 setae, m 6–8, 7 setae, m 1+2 about 200 setae, m 3+4 about 150 setae, cu+an about 150 setae.

Legs. Fore tibia bearing single spur, 27–35, 33μm long. Combs of mid tibia 23–32, 26μm wide with 24–28, 26 μm long spur, and 34–38, 36 μm wide with 25–30, 27 μm long spur; combs of hind tibia 37–39, 38μm wide with 28–43, 36 μm long spur, and 40–42, 41 μm wide with 35–38, 37 μm long spur. Tarsomere 1 of mid leg with one sensillum chaeticum. Lengths (in μm) and proportions of legs as in Table 2.

Abdomen ( Figs 3A, E). Tergite IX 88–110, 98 μm long, with 6–10, 8 median setae at base of anal point, and with eight strong setae along posterior margin ( Fig. 3E); anal tergite bands of V-type, well developed and separated, without basal branches.

Hypopygium ( Fig. 3). Anal point 38–48, 43 μm long, subtriangular, with rounded apex, bearing 3–4, 3 lateral setae on each side; crests basally broad and apically opened. Transverse sternapodeme 36–48, 41 μm long, with distinct, curved oral projections. Phallapodeme 68–84, 77 μm long. Gonocoxite 118–130, 125 μm long. Gonostylus 102–115, 108 μm long, crescent-shaped with blunt apex. Superior volsella ( Fig. 3C) 46–48, 47 μm long, ovate, with two anteromedian setae and 3– 5, 4 dorsal setae. Digitus ( Figs 3A, C) nearly reaching apex of superior volsella, gradually tapered to almost pointed apex (left) or curved column with blunt apex (right), bearing one seta located on minute tubercle near apex. Median volsella ( Fig. 3D) 69–72, 70 μm long, close to but not reaching apex of inferior volsella; stem covered by simple setiform lamellae, and with several separated petal-shaped lamellae and a few simple setiform lamellae apically; these petal-shaped lamellae all with slender tips. Inferior volsella 83–87, 85 μm long, curved and slightly swollen in apical portion, with microtrichia. HR 1.10–1.20, 1.15. HV 2.41–2.59, 2.53.

Female and immatures. Unknown.

Remarks. The new species resembles R. parvicrinis ( Tokunaga, 1938) by having similar shapes of the inferior volsella, gonostylus and the apical setae of median volsella, but can be separated from the latter species by the anal point subtriangular with rounded apex and the median volsella nearly reaching the apex of inferior volsella, whereas in R. parvicrinis the anal point is not triangular, and the median volsella does not reach the apex of superior volsella.

Distribution. China (Yunnan).