Stempellina radoszkowskii sp. nov.

http://zoobank.org/ urn:lsid:zoobank.org:act: F90C1ED3-A009-432A-94B6-BD34FE2AA118

(Fig. 9A–E)

Type material. Holotype, adult male: North Korea, Paektu Mountain, Samdžijŏn at Samji Lake (41°50'N 128°20'E; ~ 1400 m a.s.l.), 23– 25.08.1992, sweep net, leg. A. Palaczyk.

Derivatio nominis. The specific epithet commemorates Oktawiusz Wincenty Radoszkowski (1820–1895), the meritorious entomologist and the first Polish discoverer of insects from Korea.

Diagnosis. Antenna with 5–6 flagellomeres, borders between flagellomeres 5–9 indistinct, ultimate segments completely fused, plume consisted of short sparse setae. Frontal tubercles robust. Hypopygial median setae absent. Anal point short and apically swollen, anal point crests thin, spinulae absent. Superior volsella extensive, apex round, with small apical protuberance. Stem of median volsella straight, with setiform and long spindle–shaped lamellae.

Description. Adult male (n = 1).

Body size. Minute species, total length ~ 2 mm. Wing length 1010 μm.

Colouration (in alcohol). Eyes, scutal stripes, postnotum and sternum light brown, remaining body parts pale yellowish, wing membrane transparent, veins a bit darker.

Head. Eyes bare, reniform, broadly separated by frons. Antenna only with 5–6 well discernible flagellomeres, borders between flagellomeres 5–9 indistinct, ultimate segments completely fused, AR ~2.6 (when flagellum measured as 6-segmented), ~2.0 (as 7-segmented), ~1.3 (as 9-segmented); plume weak, consisted of short and sparse setae (Fig. 9A). Frontal tubercles robust, ~30 μm long and ~10 μm wide at base, conical, with apex rounded. Length of palpomeres 2–5 (μm): 32, 66, 72, 117. Clypeus with 16 setae.

Thorax chaetotaxy. Setae weak, poorly observable; Ac not observed, likely absent, Dc 7–8, Pa 1, Scts 2 (pair of setae placed medially).

Wing. Squama bare, anal lobe reduced, cell m 3+4, distal part of cells m 1+2 and r 4+5 with macrotrichia, cell r 4+5 with a single row of macrotrichia in 3/4 distal part; veins C, R, R 1, R 4+5 (distal 1/4–1/2 part), M 1+2 (distal 3/4 part), Cu 1 and false vein above M 3+4 always with macrotrichia; An and false vein under Cu 1 (distal part) usually with some macrotrichia, other veins bare; M 3+4 ending distinctly distal of R 4+5.

Legs. Fore leg tibia with s-shaped spur (~5 μm long). Combs of mid and hind leg tibiae fine, each bearing spur: straight and equally long (~20 μm) on mid leg, and unequal on hind leg - longer spur (~40 μm) slender and evenly curved, shorter spur (~16 μm) straight; ta 1 of p 2 bearing 2 hook–shaped sensilla chaetica. For length of legs segments and legs ratios see Table 1.

Hypopygium. Gonostylus (~75 μm) as long as gonocoxite. Anal tergite with bands V-shaped broadly separated and 2–3 posterolateral setae, median setae absent. The tergite tapering towards short and apically slightly swollen anal point, anal point crests thin, spinulae absent (Fig. 9B, C). Superior volsella extensive, broadest at base, tapering towards round apex bearing small apical protuberance; 3 setae on anteromedian margin (Fig. 9B, D, E). Stem of median volsella straight, ~30 μm long, with setiform and long spindle–shaped lamellae reaching tip of inferior volsella (Fig. 9B, E). Inferior volsella slightly curved, parallel-sided, with distal part rounded (Fig. 9B, E).

Remarks. Except for a combination of hypopygial characters given in the diagnosis, the adult male of Stempellina radoszkowskii differs from all known Stempellina by lower number of antennal flagellomeres. This character was recently analysed in extant and fossil species of the genus (Zakrzewska et al. 2020), as well as in Stempellinella (Zakrzewska & Jankowska 2021) . A distinct trend towards reduction of the number of flagellomeres (12 or less) in extant species relative to those of fossil is confirmed here.