Rheotanytarsus oss Cranston, 1997

Liu, Wen-Bin, Yao, Yuan, Chang, Tong, Yan, Chun-Cai & Lin, Xiao-Long, 2022, Contribution to the knowledge of Rheotanytarsus pellucidus species group from China (Diptera, Chironomidae): three new and one newly recorded species, Zootaxa 5188 (2), pp. 145-156 : 151-152

Rheotanytarsus oss Cranston, 1997

( Figs 1C , 4A–E )

Rheotanytarsus oss Cranston, 1997: 722 ; Kyerematen, Saether & Andersen, 2000: 163

Specimens examined: One male ( NKU: MHMA02 ), China, Yunnan, Xishuangbanna, Menghai, Meng’ang , 6.v. 2013, sweep net, leg. X.L. Lin.

Diagnosis. The species can be distinguished from known species of Rheotanytarsus by the following combination of characters: antenna with 13 flagellomeres; anal tergite bands of V-type and separated; anal point slightly constricted in the middle and swollen apically; superior volsella bulb-like, with one knob-like structure dorsally; the stem of median volsella curved, with five thin and long setae apically; inferior volsella curved and mostly with equal width.

Description. Adult male (n = 1)

Total length 1.69 mm. Wing length 0.95 mm. Total length/wing length 1.77. Wing length/length of profemur 1.84.

Colouration ( Fig. 1C ). Thorax pale yellow, with pale brown stripes and postnotum brown, the femur and tibia of fore leg brown, mid and hind legs brown except the basal half of femur pale yellow.

Head. Antenna with 13 flagellomeres, ultimate flagellomere 68 μm long. AR 0.16, relatively small. Temporal setae 7. Clypeus with 15 setae. Tentorium 81 μm long, 13 μm wide. Palpomere lengths (in μm): 26, 26, 54, 72, 136; Pm5/ Pm3 2.52. Third palpomere with 2 sensilla clavata distally.

Thorax. Dorsocentrals 7; acrostichals 8; prealar 1. Scutellum with 4 setae.

Wing ( Fig. 4A ). VR 1.56. Brachiolum with one seta, Sc bare, R with 11 setae, R 1 with 17 setae, R 4+5 with 35 setae, M 1+2 with 33 setae, M 3+4 with 20 setae, false vein with 84 setae, Cu with 11 setae, Cu 1 with 11 setae, PCu with 36 setae, An with 17 setae, remaining veins bare. Cell r 4+5 with c. 250 setae, m with two setae, m 1+2 with c. 150 setae, m 3+4 with c. 100 setae, cu+an with c. 120 setae.

Legs. Fore leg bearing single tibial spur, 24 μm long. Combs of mid tibia 23 μm wide with 18 μm long spur, and 29 μm wide with 18 μm long spur; combs of hind tibia 31 μm wide with 23 μm long spur, 34 μm wide with 28 μm long spur. Tarsomere 1 of mid leg with four sensilla chaetica. Lengths (in μm) and proportions of legs as in Table 3 .

Hypopygium ( Figs. 4B–E ). Tergite IX 64 μm long, with five weak median setae at base of anal point; anal tergal bands of V-type, with a small tilt angle, and with a little bit of basal bands. Anal point 26 μm long, slightly constricted in middle and swollen apically with rounded apex, bearing seven lateral setae on each side; crests of V-type and opened, nearly reaching apex of anal point. Transverse sternapodeme 32 μm long, with oral projections. Phallapodeme 56 μm long. Gonocoxite 77 μm long. Gonostylus 74 μm long, gradually tapered, with rounded apex. Superior volsella ( Fig. 4D ) 31 μm long, bulb-like, with two anteromedian setae, three dorsal setae on a knob-like structure on the dorsal, and one ventral seta near base. Digitus reduced and not visible. Median volsella ( Fig. 4E ) 99 μm long, well reaching beyond apex of inferior volsella; stem curved, covered with simple setae, and with five long foliate setae apically. Inferior volsella 59 μm long, curved and mostly with equal width, with microtrichia. HR 1.04. HV 2.28.

Remarks. Rheotanytarsus oss is recorded in China for the first time. The Chinese specimen fits well with the original description in Cranston (1997) and the review of the pellucidus species group (Kyerematen et al. 2000). Neither of the two studies described and figured the digitus, we found that reduced, and one ventral seta present in the Chinese specimen.

Distribution. Australia, Thailand and China (Yunnan).

Figures

FIGURE 1. Adult males of Rheotanytarsus pellucidus species group. A. Rheotanytarsus ashei Yao & Liu sp. n., lateral view; B. Rheotanytarsus pinderi Yao & Liu sp. n. lateral view; C). Rheotanytarsus oss, dorsal view; D. Rheotanytarsus vallenduuki Yao & Liu sp. n., lateral view. Scar bars = 500 μm.

FIGURE 4. Rheotanytarsus oss Cranston. A. wing; B. hypopygium, dorsal view; C. hypopygium, ventral view; D. superior volsella; E. median volsella.