Plesioaxymyia imprevista Polevoi, 2025

Polevoi, Alexei, Burdíková, Nikola & Ševčík, Jan, 2025, New species of Plesioaxymyia Sinclair (Diptera, Axymyiidae) from the Palaearctic Region, including an updated molecular phylogeny of the family, ZooKeys 1236, pp. 297-315 : 297-315

Plesioaxymyia imprevista Polevoi sp. nov.

Figs 2 A – C , 3 A – C

Specimens examined.

Holotype. Russia • ♀; Karelia, Paanajarvi National Park, Vartolambina ; 66.246°N, 30.555°E; 80 m a. s. l.; 1–27 Jun. 2021; A. Protasova leg.; Malaise trap; GenBank: accession numbers PV 036313, PV 036316, PV 036319, PV 036317, PV 035246, PV 037681; ZISP, INS_DIP_0001011 .

Differential diagnosis.

Medium-sized, dark brown species (Fig. 2 A ); wings hyaline with dark elongated pterostigma, covering apical half of vein R 1; legs yellowish-brown with darkened tarsi, femora and tibiae darkened apically. Similar to Plesioaxymyia vespertina , from which it is distinguished by details of female terminalia: sternite 8 with smoothly rounded dorsoapical margin (forming somewhat protruding dorsoapical corner in P. vespertina ) and completely reduced basal segment of cerci (distinct in P. vespertina ).

Description.

Head. Head dark brown. Face sunken, clypeus convex, mouthparts brown. Palpus brown, 5 - segmented, with short (almost hidden) first segment and broadened third segment. Compound eye densely covered with short ommatrichia; divided by fine groove into upper and lower hemispheres of unequal size and with deep triangular excision opposite antennal base (Fig. 2 B ). Three ocelli arranged in equilateral triangle, placed on elevated tubercle. Frons with a few brownish hairs above antennal bases and between ocellar triangle and compound eye. Posterior part of head with numerous brownish hairs. Antenna 16 - segmented, brown; pedicel yellowish apically; middle flagellomeres about twice as wide as long.

Thorax. Mesonotum dark brown, thinly dusted, lacking any larger setae but covered with tiny yellowish hairs; a pair of narrow transverse shiny patches present along prescutal suture (Fig. 2 B ); prescutum yellowish laterally. Scutellum yellowish-brown, strongly convex, with short hairs along posterior margin. Pleura brown.

Wing. Wing length 4.08 mm. Wing hyaline with light brownish tinge (Fig. 2 C ); brown elongated pterostigma occupies apical half of R 1. Costa hardly produced beyond R 4 + 5. Sc curved into costa proximally to Rs; Sc-r reduced. Rs with kink; R 2 + 3 forked well beyond apex of R 1, R 2 deviates in slightly obtuse angle. Crossvein r-m perpendicular to R 4 + 5. M 1 + 2 branching slightly before apex of R 1; section of M-stem distal to r-m about as long as M 1, longer than M 2 and about twice as long as its section proximal to r-m. M 4 straight; CuA distinctly sinuous. CuP short, scarcely reaching beyond posteromedial angle of wing. Anal lobe well-developed. Macrotrichia on wing veins not visible. Halter brown.

Legs. Coxa, trochanters, femora and tibiae yellowish-brown; all femora and tibiae darkened apically; tarsi brownish. Hind tibia slightly curved in middle, with brush of bristly hairs posteroapically. Ratio of basitarsus to tibia: bt 1: t 1 – 0.45, bt 2: t 2 – 0.43, bt 3: t 3 – 0.30. Tibial spurs not developed.

Abdomen. Abdomen brown. Tergites 1–7 with sparse hairs posteriorly. Terminalia (Fig. 3 ) brown. Tergite 8 approximately one-third length of sternite 8, rounded and setose apically; sternite 8 lengthened, tapered apically, with sparse short hairs. Cercus one-segmented; basal segment not developed; apical segment about 4 times longer than wide, bearing ca. 10 setae.

Etymology.

The species epithet is from the Latin imprevistus (unexpected, unforeseen), stressing that the finding of this species in Northwest Russia was a real surprise.

Distribution.

The species is currently known only from the type locality in Russian Karelia (Northwest Russia).

Biology.

The adult was collected with a Malaise trap set in Vaccinium myrtillus type pine- and spruce-dominated forest. The larval biology is unknown.

Figures

Figure 2. Plesioaxymyia imprevista sp. nov., female holotype A habitus, lateral view B head and thorax, oblique anterodorsal view C wing. Abbreviations: CEE – triangular excision of compound eye; CuA – anterior branch of cubital vein; M 1, 2, 4 – medial veins; R 2, 3, 4 + 5 – radial vein; Sc – subcostal vein; TSP – transverse shiny patch of mesonotum. Scale bars: 1 mm (A, С); 0.3 mm (B).

Figure 3. Plesioaxymyia imprevista sp. nov., female terminalia A lateral view B dorsal view C ventral view. Abbreviations: cerc — cercus; st 7, 8 — sternites; tg 7, 8 — tergites. Scale bars: 0.2 mm (A – C).