Rheotanytarsus yamamotoi Lin & Yao, 2024

Sun, Li, Wang, Ruihao, Yao, Yuan, Sun, Bingjiao & Lin, Xiaolong, 2024, Review of the Rheotanytarsus acerbus species group from China (Diptera: Chironomidae), Zoological Systematics 49 (4), pp. 343-351 : 6-8

Rheotanytarsus yamamotoi Lin & Yao , sp. nov.

( Figs 1C, 4)

Material examined. Holotype ♂ ( SHOU: XL1400 ), China, Sichuan, Dujiangyan, Tai’an, Qingchenghoushan Scenic Area , 30.9257°N, 103.4928°E, elev. 920 m, 27.VII.2015, sweep net, leg. B.J. Sun. Paratype. 1♂ ( SHOU: XL526 ), China, Hainan, Changjiang, Bawangling National Nature Reserve , 19.11463°N, 109.08419°E, elev. 142 m, 12.III.2016, leg. B.J. Sun.

Etymology. The specific name refers to Dr. Masaru Yamamoto, for his contribution to Japanese Chironomidae .

Diagnosis. The adult male can be distinguished from other species of acerbus group by the following combination: AR 0.65–0.73; anal tergite bands of V-type, distinctly branched, anteriorly fused; anal point constricted in the middle, with rounded lanceolate apex, anal crests of Y-type, basally broad and apically opened; superior volsella with a subtriangular apical extension, which tapers to a sharp point; the stem of median volsella bent at right angle, with relatively small lamellae fused into a plate on apex.

Description. Adult males (n = 2, except stated). TL 2.15–2.50 mm. WL 1.20–1.27 mm. TL/WL 1.80–1.97. WL/length of profemur 1.76–1.77.

Coloration. Thorax, legs, and abdomen pale yellow.

Head. Ultimate flagellomere 291–351 μm long. AR 0.65–0.73. Temporal setae 9. Clypeus with 14–15 setae. Tentorium 72–97μm long, 15–18μm wide. Palpomere lengths (in μm): 27–44, 33–37, 91–93, 98–106, -. Third palpomere with 2 sensilla clavata distally.

Thorax. Ac 8–10, 10; Dc 7; Pa 1, Scts 6.

Wing ( Fig. 1C). VR 1.37–1.39. Brachiolum with one seta, Sc with one seta, R 18–21 setae, R 1 20–27 setae, R 4+5 46–48 setae, M 1+2 32–40 setae, M 3+4 27–31 setae, false vein 64–70 setae, Cu 14 setae, Cu 1 18–20 setae, PCu 30–43 setae, An 26– 29 setae, remaining veins bare. Cell r 4+5 about 200 setae, m 6–7 setae, m 1+2 about 200 setae, m 3+4 about 100 setae, cu+an about 140 setae.

Legs. Fore tibia bearing single spur, 19–20μm long. Combs of mid tibia 18–21 μm wide with 21–33 μm long spur, and 21–23 μm wide with 23–30 μm long spur; combs of hind tibia 23–27 μm wide with 33–36 μm long spur, and 22–23 μm wide with 36–39 μm long spur. Tarsomere 1 of mid leg of the paratype with four sensilla chaetica. Lengths (in μm) and proportions of legs as in Table 3.

Abdomen ( Fig. 4A). Tergite IX 74–78 μm long, with 2–5 median setae at base of anal point, anal tergite bands of Vtype, distinctly branched, fused anteriorly.

Hypopygium ( Fig. 4). Anal point 26–29 μm long, constricted in middle and with rounded lanceolate apex, bearing three lateral setae on each side; crests basally broad and apically opened, the apical half nearly parallel-sided. Transverse sternapodeme 31–36 μm long, with straight projections. Phallapodeme 64–82 μm long. Gonocoxite 92–104 μm long. Gonostylus 87–91 μm long, gradually tapered and curved. Superior volsella ( Fig. 4C) 33–36 μm long, ovoid, with a subtriangular apical extension, which tapers to a sharp point, and with two anteromedian setae and 4–5 dorsal setae. Extension of superior volsella more pronounced and sharper in paratype. Digitus fang shaped with almost pointed apex, bearing one seta located on cylindrical tubercle in middle. Median volsella ( Fig. 4D) 44–49 μm long, close to but not reaching apex of superior volsella, with three setiform lamellae fused into a fan-shaped plate; plate covered by three setiform lamellae dorsally; stem obliquely inward and bent at right angle near apex, covered by setiform lamellae. Inferior volsella 60–61 μm long, curved and basally swollen, with microtrichia. HR 1.01–1.20. HV 2.36–2.88.

Female and immatures. Unknown.

Remarks. The new species resembles R. samaki Lehmann, 1979 by having similar shapes of superior volsella and gonostylus, but can be separated from the latter species by the anal point with rounded lanceolate apex, and the stem of median volsella markedly being curved, with relatively small lamellae fused into a plate on apex, whereas in R. samaki , the anal point is tapered to pointed apex, and the median volsella has lined stem and does not have apical plate.

Distribution. China (Hainan, Sichuan).

Key to known males of the R. acerbus species group.

1.

2.

3.

4.

5.

6.

7.

Gonostylus with curved apex ............................................................................................................................................................... 2

Gonostylus not curved .........................................................................................................................................................................3

Tergite IX with about 20 setae; digitus present ..................................................................................... R. acerbus ( Johannsen, 1932)

Tergite IX with 8 setae; digitus absent ................................................................................................ R. aphelus Wang & Guo, 2004

Gonostylus with pointed apex .............................................................................................................................................................. 4

Gonostylus with rounded apex............................................................................................................................................................. 5

Median volsella with two leaf-like plates; anal tergite bands horizontal.............................................. R. adjectus ( Johannsen, 1932)

Median volsella with one small and rounded plate; anal tergite bands of V-type........... R. acuminatus Kyerematen & Saether, 2000

Digitus absent..................................................................................................................................... R. parvicrinis ( Tokunaga, 1938)

Digitus present .....................................................................................................................................................................................6

AR relatively low, about 0.3; superior volsella with rounded apex; tergite IX with eight strong setae .................................................. ................................................................................................................................................ R. cangshanensis Lin & Yao , sp. nov.

AR relatively high, larger than 0.6; superior volsella with pointed apex; tergite IX with only microtrichia ........................................7

Superior volsella with three characteristic extensions; anal tergite bands separated; anal point tapered to pointed apex ...................... ................................................................................................................................................................... R. samaki Lehmann, 1979

Superior volsella with one apical extension; anal tergite bands fused; anal point with rounded lanceolate apex................................... ...................................................................................................................................................... R. yamamotoi Lin & Yao , sp. nov.

Funding The work is financially supported from the research start-up fund project for young teachers of Shanghai Ocean University (A2-2006-23-200303), National Natural Science Foundation of China (31900344) and the China Postdoctoral Science Foundation Grant (2018M640227).

Acknowledgements

We are grateful to Dr. Fanqing Kong for his effective collecting in field.