Rheotanytarsus adjectus ( Johannsen, 1932 )

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 : 2-5

Rheotanytarsus adjectus ( Johannsen, 1932) ( Figs 1A, 2)

Tanytarsus adjectus Johannsen, 1932: 547 .

Rheotanytarsus adjectus (Johannsen) : Thienemann In: Zavrel & Thienemann, 1934: 146, 153–154; Kyerematen et al., 2000: 233.

Material examined. 3♂ ( SHOU: WZSM08 - WZSM10 ), China, Hainan, Wuzhishan, Shuimanxiang , 18.88388°N, 109.66448°E, elev. 644 m, 9.XII.2010, leg. F.Q. Kong.

Diagnosis. The adult males can be distinguished from other species of acerbus group by the following combination: AR 0.33–0.42; anal tergite bands branched and horizontal; the base of anal point with relatively dense setae, anal point crest well developed; gonostylus oval, relatively broad, with a pointed apex; superior volsella rounded, triangular in apical portion, with an r-shaped fold on the ventral side, and the digitus absent; median volsella with two leaf-like plates, both with crisscross vein-like structures ( Johannsen, 1932; Kyerematen et al., 2000).

Description. Adult males (n = 3, except stated). TL 1.78–1.83 (2) mm. WL 1.09–1.19, 1.12 mm. TL/WL 1.80–1.97 (2). WL/length of profemur 1.64–1.67, 1.66.

Coloration. Thorax tawny with dark brown stripes, abdomen and legs tawny.

Head. Ultimate flagellomere 159–187, 178 μm long. AR 0.33–0.42, 0.38. Temporal setae 6–7, 7. Clypeus with 18–20, 19 setae. Tentorium 80–96, 87 μm long, 14–18, 16 μm wide. Palpomere lengths (in μm, n = 2): 25–29, 29, 78–80, 77, 142– 143; Pm5/Pm3 1.78–1.83. Third palpomere with 2 sensilla clavata distally.

Thorax. Ac 8–9, 9; Dc 7–8, 8; Pa 1, Scts 4 (2). Halteres with 5–6 (2) setae.

Wing ( Fig. 1A). VR 1.67–1.78, 1.72. Brachiolum with one seta, Sc bare, R with 15–17, 16 setae, R 1 23–28, 25 setae, R 4+5 54–60, 56 setae, M 1–2, 1 seta, M 1+2 50–57, 54 setae, M 3+4 26–28, 27 setae, false vein about 100 setae, Cu 18–21, 19 setae, Cu 1 14–17, 16 setae, PCu 61–64, 63 setae, An 26–29, 27 setae, remaining veins bare. Cell r 4+5 about 350 setae, m 4– 8, 6 setae, m 1+2 about 300 setae, m 3+4 about 130 setae, cu+an about 150 setae.

Legs. Fore tibia bearing single spur, 18–26, 22μm long. Combs of mid tibia 15–26, 20μm wide with 16–22, 20 μm long spur, and 26–31, 29 μm wide with 17–20, 19 μm long spur; combs of hind tibia 31–33, 32μm wide with 25–27, 26 μm long spur, and 36–37, 36μm wide with 28–29, 28 μm long spur. Tarsomere 1 of mid leg with 4–5, 4 sensilla chaetica. Lengths (in μm) and proportions of legs as in Table 1.

Abdomen ( Fig. 2A). Tergite IX 87–97, 93 μm long, with 13–18, 15 median setae densely distributed at base of anal point, anal tergite bands branched and horizontal.

Hypopygium ( Fig. 2). Anal point 23–25, 24 μm long, gradually tapering towards rounded apex, bearing 4–5, 5 lateral setae on each side; crests of V-type, separated and developed basally, and fused apically. Transverse sternapodeme 25–33, 28 μm long, with distinct oral projections. Phallapodeme 58–69, 64 μm long. Gonocoxite 83–101, 89 μm long. Gonostylus 97–113, 103 μm long, relatively broad in middle, with a pointed apex. Superior volsella ( Fig. 2C) 36–45, 41μm long, rounded, triangular in apical portion, with two weak anteromedian setae and 5–6, 5 weak dorsal setae; an r-shaped fold appearing on ventral side of superior volsella. Digitus absent. Median volsella ( Fig. 2D) relatively short (34–43, 37 μm), not reaching apex of superior volsella; stem with several simple setiform lamellae along inner margin; two leaf-like plates emerging from middle of stem, and both with crisscross vein-like structures; plates stacking together, herein illustrated one of them. Inferior volsella 61–69, 65 μm long, with microtrichia. HR 0.84–0.89, 0.87. HV 1.83–1.85, 1.84.

Remarks. The species is recorded in China for the first time. The Chinese specimens fit well with the original description ( Johannsen, 1932), especially the characteristic median volsella.

Distribution. China (Hainan), Indonesia.