Penthetria sp.

Skartveit, John, 2021, A new fossil species of the genus Bibio, with an update on bibionid flies from Baltic and Rovno amber (Diptera, Bibionidae), Deutsche Entomologische Zeitschrift 68 (1), pp. 81-99 : 81

Penthetria sp. Figs 3 , 18

Material.

Female, SDEI Dip-00823 - CCHH#1789-4, embedded in a clear amber block which has undergone autoclave treatment (C. Hoffeins, in litt.).

The species differs from Penthetria montanaregis in the following aspects: smaller, wing length about 4.5 mm, wing narrower, more than 3 times as long as wide (in bibionids, females generally have wider wings than conspecific males) with reduced anal lobe, R2+3 placed more distally so that the segment R2-5 is almost as long as R4+5 (less than half as long in P. montanaregis ), fork of M strongly asymmetrical (nearly symmetrical in P. montanaregis ), CuA2 apically strongly curved basad (moderately curved basad in P. montanaregis ). It differs from female Penthetria integroneura Skartveit, 2009 most conspicuously by the presence of R2+3 and by the more strongly curved CuA-veins, also by the presence of strong setae dorsally on the thorax and apparently by the head shape, though the latter is likely affected by autoclave treatment.

Description.

Male unknown.

Female (N = 1): Total length 5.0 mm. The specimen is of a uniform, dark colour, likely affected by the autoclaving.

Head: length 0.58 mm. Apparent shape probably affected by autoclaving, outline of complex eye not possible to see. Flagellum 0.42 mm long, 0.07 mm wide, 7-segmented, shape of flagellomeres obviously affected by autoclaving. Palp relatively long, outer segments appear to be very slender, but this is likely an artefact caused by autoclaving.

Thorax: Length 1.18 mm. Dorsally with some relatively long and strong, erect setae, details otherwise not possible to make out. Haltere light brown.

Legs: relatively long, femorae slightly clavate, tibiae apparently very slender (possibly affected by autoclaving). The legs are clad with relatively long, brown pile, on tibiae about as long as the tibia’s width. Tibial spurs fine and sharp. Segment measurements, all inn mm: fore femur length 1.37, width 0.16, fore tibia length 1.32, width 0.12, mid femur length 1.23, hind femur length 1.69, width 0.18, hind tibia length 1.71, width 0.13, hind first tarsomere length 0.63, width 0.07.

Wing (Fig. 18 ): Length 4.6 mm, width 1.5 mm, length/width = 3.1. Brown fumose, relatively slender, veins brown throughout, R-veins considerably more robust than M- and CuA-veins. Costa relatively strong with rather long setules which at least basally are longer than the width of the vein, extending a little past half-way between apices of R4+5 and M1. Humeral vein present, oblique. Pterostigma relatively small, oval, brown. Subcosta fine but distinctive, straight. R2+3 oblique, almost straight, a little less than half as long as R4+5, which is gently curved. Rs straight, nearly three times as long as R-M, which is vertical. R2-5 (basally of R2+3) almost as long as R4+5 (distally of R2+3). M basally connected to CuA. M-veins fine, M and M2 form an approximately straight line with M1 diverging forward from this. CuA1 apically slightly, CuA2 strongly bent basad. CuP parallel to CuA/CuA2, fine but does reach wing margin. Anal lobe strongly reduced, basal-posterior edge of the wing nearly straight-lined. Vein lengths, all in mm: Subcosta 2.48, Basal R 1.46, R1 1.44, Rs 0.53, R2-5 1.09, R2+3 0.58, R4+5 1.27, R-M 0.19, basal M 1.41, distal M 0.44, M1 1.85, M2 1.41, M-CuA 0.14, CuA 1.02, CuA1 1.99, CuA2 1.18. The wings have numerous, transverse cracks probably caused by autoclaving, this has not altered the overall shape, though.

Abdomen: Length 3.6 mm, dark, cylindrical, with fine, dark, short pile. Shape of terminalia difficult to make out, probably affected by autoclaving.

Discussion.

The specimen of this species is obviously affected by autoclave treatment, particularly so in the head where the overall shape appears changed, the outlines of the complex eyes are not possible to make out, and the shapes of the antennal and palp segments are strongly disrupted. The autoclaving appears also to have altered the appearance of the terminalia, and possibly thorax and legs to some extent. However, the wing characters appear to be uncompromised and should be sufficient to recognise the species, at the very least to differentiate it from the other species of Penthetria known from Baltic amber. Identifying Penthetria species based on female specimens is very difficult in recent species and this is probably so in fossil species, too, hence this specimen is not given a formal name at this stage.

Figures

Figure 3. Penthetria sp., female. SDEI Dip- 00823 - CCHH 1789 - 4. Photo: Christel and Hans-Werner Hoffeins.

Figure 18. Penthetria sp., female, wing. Scale bar: 1 mm.