Archistempellina bifurca Giłka et Zakrzewska, 2013

Giłka, Wojciech, Zakrzewska, Marta, Dominiak, Patrycja & Urbanek, Aleksandra, 2013, Non-biting midges of the tribe Tanytarsini in Eocene amber from the Rovno region (Ukraine): a pioneer systematic study with notes on the phylogeny (Diptera: Chironomidae), Zootaxa 3736 (5), pp. 569-586 : 571-573

Archistempellina bifurca Giłka et Zakrzewska , sp. nov.

Type material. Holotype. Adult male (tarsus of left fore leg and right mid leg missing) in 8 x 6 x 4 mm piece of amber (SIZ K-26075, Fig. 1 A).

Derivatio nominis. From Latin, meaning ‘forked’, in reference to the shape of the hypopygial median volsella armed with two slender lamellae.

Diagnosis. Tibia of fore leg with small spur; femur of mid leg longer than femur of hind leg. Anal point tapering to pointed apex, reaching over superior and median volsellae and over half length of inferior volsella. Superior volsella very small, cylindrical. Stem of median volsella longer than its falciform lamellae.

Description. Adult male (n = 1). Total length 2.7 mm; wing length c. 1400 Μm.

Head ( Fig. 1 B–D). Eyes bare, with well developed dorsomedian extensions. Frontal tubercles not observed. Antenna with 13 well discernible flagellomeres, AR 1.12–1.15, plume fully developed ( Fig. 1 C, D). Palps slightly asymmetrical, length of palpomeres 2–5 (Μm): 48, 123, 147, 205–245. Clypeals unobservable.

Thorax ( Fig. 1 B). Antepronotum relatively well developed, scutum not overreaching antepronotum. Tubercle on scutum absent. Most of setae unobservable, at least 8 scutellars.

Wing ( Fig. 1 E). Slender, with anal lobe weak, broadest at 2/3 length, width: 387 Μm, length/width ratio 3.62. RM slightly oblique relative to R. Sc unobservable. R1 and R2+3 arcuate. FCu placed distally of RM; VR Cu 1.25. Veins ending as follows (in order from base to tip): An, Cu1, R1, R2+3, M3+4, R4+5, M1+2; distances between ends of R1–R2+3 and R2+3–R4+5 unequal (VR C c. 4); An reaching FCu at least. Wing membrane covered with dense macrotrichia in distal half.

Legs. Tibia of fore leg with small spur, c. 10 Μm long. Single tibial comb of mid leg fan-shaped, teeth up to 20 Μm long, with single slender c. 40–45 Μm long spur; combs of hind leg broadly separated, fan-shaped, one comb broad (composed of c. 15 teeth) up to 20 Μm long, without spur, second comb narrow, teeth up to 25 Μm long, bearing c. 50 Μm long spur. Sensilla chaetica on ta1 of p2 not observed. Pulvilli absent. For length of leg segments and leg ratios see Table 1 .

Hypopygium ( Fig. 1 F–K). Gonostylus cylindrical, straight, c. 115 Μm long, distinctly longer than gonocoxite, with strong apical seta. Anal tergite subtriangular, bearing several strong median setae. Anal point slender, styliform, tapering to pointed apex, without spinulae and crests, bearing at least 4 posterolateral setae on each side; anal point reaching over superior and median volsellae and over half length of inferior volsella; upturned in lateral view with tip bent down ( Fig. 1 F–I). Superior volsella extraordinarily small, cylindrical, slightly swollen in distal part, bearing at least 2 setae at rounded apex ( Fig. 1 J). Digitus absent. Stem of median volsella about the size and shape of superior volsella, c. 20 Μm long, slightly curved, medially directed, bearing 2 slender falciform lamellae; stem distinctly longer than lamellae ( Fig. 1 K). Inferior volsella reaching 1/3 length of gonostylus at most, clubshaped, with distinctly enlarged head-like apical half, armed with several stout curved setae.

Remarks. The best diagnostic characters that allow the separation of Archistempellina bifurca and A. falcifera are the shape of the anal point, the arrangement/position of the anal point apex in relation to the hypopygial volsellae (cf. Fig. 1 F, G, I and Fig. 2 E, G, H), and the lamellae/stem length proportions in median volsellae (cf. Fig. 1 K and 2J).

Figures

FIGURE 1. Archistempellina bifurca sp. nov., male. A— holotype (inclusion); B— habitus; C, D— antenna (D— photographed using Nomarski DIC); E— wing; F – K— hypopygium: F, I— dorsal aspect; G— ventral aspect; H— lateral aspect; J— superior volsella; K— median volsella (J, K— magnified three times relative to hypopygium drawn).

FIGURE 2. Archistempellina falcifera sp. nov., male. A — holotype (inclusion); B — habitus; C — antenna; D — wing; E – J — hypopygium: E, G — ventral aspect; F — lateral aspect; H — anal point; I — superior volsella, J — median volsella (H – J — magnified c. three times relative to hypopygium drawn).

Tables

TABLE 1. Leg segment lengths (µm) and leg ratios of male Archistempellina bifurca sp. nov.

fe	ti ta1	ta2	ta3	ta4	ta5	LR
P1 585	395–410 760	-	-	255	85	1.85
P2 685	560 400	195	140	90	60	0.71
P3 645	595 520	285	240	140	80	0.87