Stempellinella gilkai, Zakrzewska & Jankowska, 2021

Zakrzewska, Marta & Jankowska, Ariadna, 2021, A new fossil Stempellinella from Eocene Baltic amber, with systematic notes and amendment of the generic diagnosis (Diptera: Chironomidae), Zootaxa 4908 (4), pp. 505-514 : 506-507

Stempellinella gilkai sp. nov.

LSID: urn:lsid:zoobank.org:act:CE2F9673-970F-4DA7-80B9-0E67AF40DF44

Type material. Holotype. Adult male (tarsi of both fore, left mid and right hind leg missing) preserved in 30 x 24 x 5 mm piece of amber ( Fig. 2A, B ) (Eocene Baltic amber, ~40–45 Ma, inventory no. F28a LSZ DIZP; IR spectrum no. 16218 IAA; Fig. 1 ). Syninclusions: Chironominae , 1 adult male (F28b LSZ DIZP), Sternorrhyncha, 1 specimen (F28c LSZ DIZP).

Derivatio nominis. Authors dedicate the specific epithet to their mentor, Prof. Wojciech Giłka, a Chironomidae specialist.

Diagnosis. Antennal flagellum composed of 13 flagellomeres. Sc ending far distal of RM; RM long, slightly oblique relative to M. Vein M 3+4 ending opposite to R 4+5. Gonostylus slightly shorter than gonocoxite. Anal point stout, with strong crests framing numerous irregularly dispersed spinulae. Superior volsella elongate, peanut-shaped. Stem of median volsella long, bearing setiform and foliate lamellae, distal lamella with elongated filiform tip reaching apex of inferior volsella. Inferior volsella with spherical bulge bearing 4 medially directed distinct setae, apical part bent medially.

Description. Adult male (n = 1).

Total length ~ 1.55 mm; wing length 945 μm.

Head ( Fig. 2B, C ). Eyes bare, without dorsomedian extension, broadly separated by frons. Frontal tubercles conical, length 8 μm, width 8 μm. Antenna with 13 flagellomeres (borders between flagellomeres 12 and 13 faintly visible but present) ( Fig. 2C ), AR 0.45, plume fully developed. Length of palpomeres 2–5 (in μm): 28, 60, 76, 117. Clypeus with at least 5 setae.

Thorax ( Fig. 2B ). Ac at least 7, Dc at least 7 on each side, Scts at least 3, Pa unobservable.

Wing ( Fig. 3 ). Slender, with anal lobe weak, broadest at 2/3 length; width: 285 μm, length/width ratio: 3.32. Sc ending well distal of RM and slightly distal of FCu, R 2+3 not visible. RM oblique relative to M. FCu placed distally of RM; VR Cu 1.36. Veins ending as follows (in order from base to tip): An, Sc, Cu 1, R 1, R 4+5 and M 3+4, M 1+2. Wing membrane and most veins (except subcosta and media) covered with macrotrichia.

Legs ( Fig. 2B ). Tibial apices with their armature faintly visible. Foreleg tibia with fine spur, up to 10 μm long. Mid- and hindleg tibia with small combs ~10 μm long. One midleg comb bearing ~20 μm long spur, both hindleg combs with spurs (~15-25 μm long). Sensilla chaetica on ta 1 of p 2 not observed. Pulvilli absent. Lengths of leg segments and leg ratios as in Table 1.

Hypopygium ( Fig. 4 A–E). Gonostylus short, ~65 μm, slightly shorter than gonocoxite, gently tapering to blunt apex armed with both strong setae and microtrichia. Anal tergite subtriangular, with 5–6 posterolateral setae on each side of anal point, several irregularly dispersed fine median setae present. Anal point long and stout, reaching posterior margin of superior volsellae apices, tapering to blunt apex, with strong crests framing 21 irregularly dispersed spinulae ( Fig. 4A, C ). Superior volsella elongate, peanut-shaped, apex with protuberances bearing up to 4 setae. Digitus not observed. Stem of median volsella long (~30 μm), more or less cylindrical with 2 subtle conical processes on apex, bearing two setiform lamellae on the proximal part and 5 to 6 foliate lamellae, distal lamella with elongated filiform tip reaching apex of inferior volsella ( Fig. 4B, D, E ). Inferior volsella reaching 2/3 length of gonostylus, with spherical bulge bearing 4 medially directed distinct setae at 1/3 of its length, with apical part bent medially, bearing several strong setae ( Fig. 4 A–C).

Figures

FIGURE 1. Fourier transform infrared spectroscopy (ATR) spectrum no. 16218 IAA obtained from the piece of Baltic amber (Eocene, ~40–45 Ma) with the examined inclusion.

FIGURE 2. Stempellinella gilkai sp. nov., holotype, adult male (F28a LSZ DIZP, Eocene Baltic amber, ~40–45 Ma): A inclusion in amber, B habitus, C head and antenna (white arrows: borders between flagellomeres). Scale bars: 1 cm (A), 500 μm (B), 200 μm (C).

FIGURE 3. Stempellinella gilkai sp. nov., holotype, adult male (F28a LSZ DIZP, Eocene Baltic amber, ~40–45 Ma): A, B wing. Scale bar: 100 μm. C—costa, Sc—subcosta, R, R1, R 4+5 —radial veins, RM—radial-median crossvein, M, M1+2, M3+4—median veins, Cu, Cu1—cubital veins, FCu—cubital crossvein, An—anal vein.

FIGURE 4. Stempellinella gilkai sp. nov., holotype, adult male (F28a LSZ DIZP, Eocene Baltic amber, ~40–45 Ma): A–C hypopygium in dorsal aspect, stacked at different depth levels (A, B) and drawn (C), D, E median volsella (magnified c. 2 times relative to hypopygium photo). Scale bars: 50 μm. MS—median setae, AnP—anal point, SVo—superior volsella, IVo—inferior volsella, Gc—gonocoxite, Gs—gonostylus.