Plecia stygia ( Heyden & Heyden, 1865 )

Skartveit, John & Wedmann, Sonja, 2021, A Revision of fossil Bibionidae (Insecta: Diptera) from the Oligocene of Germany, Zootaxa 4909 (1), pp. 1-77 : 38

Plecia stygia ( Heyden & Heyden, 1865) (figs. 59–60, 169–171)

Protomyia stygia Heyden & Heyden 1865: 24 .

Protomyia veterana Heyden & Heyden, 1865: 25 . Syn.n.

Localities: Rott.

Material examined: Syntypes of Protomyia stygia NHMUK 58808 (fig. 59), 58809. Holotype of Plecia veterana NHMUK In 58796 (fig. 60).

Additional material LACMIP 2533.294 / LACMIP Type 3426, 2533.295 / 3427, 2533.1063ab, 2533.1071ab, 2533.1072, 2533.1146ab, 2533.1148ab, 2533.1156ab, 2533.1159ab, 2533.1168ab, 2533.1173, 2533.1175ab, 2533.1178ab, 2533.1186ab, 2533.1188ab, 2533.1189, 2533.1191, 2533.1192, 2533.1193, 2533.1197, 2533.1200, 2533.1202, 2533.1203ab, 2533.1206, 2533.1223, 2533.1224, 2533.1232ab, 2533.1282ab, 2533.1283, 2533.1285ab, 2533.1300ab, 2533.1303ab, 2533.1306ab, 2533.1313ab, 2533.1317ab, 2533.1321, 2533.1322ab, 41997.109ab, 41997.222ab. Isolated wings: LACMIP 2533.1204ab.

Description:

Female (N=50, figs. 59–60, 169–171):

Total length 4.9–7.0 mm (N=35). Body short and squat.

Head: Length about 0.65–0.85 mm (some specimens have measurements outside this range, but this is likely due to postmortem deformation), width about 0.7–0.9 mm Blackish-brown, complex eye rather large, oval. Antenna conical, flagellum 7-segmented, 0.41–0.53 mm long (N=12). Palpus dark brown, rather slender. Ocellar triangle tall and prominent.

Thorax: Length 1.6–2.2 mm (N=44), width 1.4–1.7 mm (N=18). Brownish-black, haltere light brown.

Legs: rather short, femora yellowish with dark tips, fore tibiae and tarsi dark brown to black. Hind tibia yellowish with dark tip, spur needle-fine, about one third the length of first hind tarsomere, hind tarsus dark brown, slender. Fore femur 1.3–2.1 mm long (N=11), 0.29–0.39 mm wide (N=8), fore tibia 1.3–1.8 mm long (N=22), 0.17–0.24 mm wide (N=15), fore first tarsomere 0.52–0.81 mm long (N=5), hind femur 1.7–2.3 mm long (N=3), hind tibia 1.7–2.3 mm long (N=20), 0.20–0.27 mm wide (N=7), hind first tarsomere 0.67–0.85 mm long (N=18).

Wing (figs. 170–171): Length 5.0– 7.4 mm (N=50), width 1.9–2.7 mm (N=46), length/width = 2.4–3.0, light grayish-brown fumose, costal cell slightly darkened. Veins rather fine. Pterostigma not apparent. Humeral vein present, oblique. Subcosta fine and straight, running some distance from R. R 2+3 rather long, oblique, basally bent. R 4+5 apically gently curved. Costa extends to apex of R 4+5. R-M vertical. M- and CuA-veins apically gently curved. CuP straight, apically converging a little towards CuA 2. Vein measurements are given in Table 4.

Abdomen: Length 3.0–5.0 mm (N=48), width 1.4–2.2 mm (N=36), blackish-brown, short and stocky. Last tergite posteriorly deeply concave. Last sternite with deep, V-shaped mesal cleft. Cerci small and rounded.

Male unknown.

Discussion:

Protomyia stygia and P. veterana supposedly differ mainly in the shape of the wing, being relatively narrow in stygia and wide in veterana . However, this character is highly dependent on taphonomy, the apparently wide types (« veterana ») being in all likelihood due to perspective shortening because they have been compressed obliquely. This is neatly illustrated by several specimens apparently having one wing of the «narrow» type and one wing of the «wide» types.