Axysta clausseni, Stuke, 2022

Stuke, Jens-Hermann, 2022, A Second European Axysta Species (Diptera: Ephydridae), Acta Zoologica Academiae Scientiarum Hungaricae 68 (2), pp. 159-168 : 161-164

Axysta clausseni sp. n.

( Figs 1 , 4–5 , 7–9 )

Holotype. Male: (1) “NDS Lüneburg / Forst nw Gudow / 28.5.2017, Stuke leg. / 2073 [cross written]”; (2) “ Holotypus / Axysta clausseni m / spec. nov. m / Stuke det. 2021”. The locus typicus is located at 53,298°N 11,000°E, and the forest is called “Bohldamm”. The specimen is pinned on a minute and, except from a missing right antenna, is in excellent condi- tion ( Fig. 1 ). The holotype is preserved in the collection of the Museum für Naturkunde – Leibniz Institute for Evolution and Biodiversity Science, Berlin, Germany ( ZMB).

Paratypes. GERMANY: 1 f, 14.iv.2007, Lower Saxony, Ahlhorner ponds [52,928°N 8,139°E]; 1 f , 30.iv.2017, Lower Saxony, Aschendorfer Obermoor S Papenburg [53,027°N 7,424°E]; 1 f , 7.v.2017, Lower Saxony, Esterwegen, Teufelsbergweg [53,011°N 7,596°E]; 1 f , 7.v.2017, Lower Saxony, Esterweger Dose [53,018°N 7,647°E]; 1 m , 28.v.2017, Lower Saxony, forest NW Gudow [53,298°N 11,000°E]; 1 m , 23.iv.2019, Lower Saxony, Heseler forest [53,306°N 7,618°E]; 1 f , 28.iii.2019, Lower Saxony, Leer, Westerhammrich [53,241°N 7,440°E]; 1 f , 1.viii.2018, Lower Saxony, “Neuer Teich” close to Zorge [51,651°N 10,629°E]; 1 f , 11.v.2008, Lower Saxony, Sumter See [53,281°N 10,894°E]; 1 f , 16.viii.2009, Lower Saxony, Thülsfelder reservoir, [52,934°N 7,924°E] ; FINLAND: 1 m 1 f , 21.vii.2020, Lapland, Vuojoki 2.5 km NNE Vuojärvi [67,106°N 26,638°E]; 1 f , 17.vii.2020, Päijät-Häme, Jääsjärvi 2.6 km NE Hartola [61,597°N 26,051°E] .

Additional material. GREAT BRITAIN: 1 m, 8.x.1977, Wales, Craig Cerrid Gleisiad NNR [51,887°N 3,497°W], ex Juncus , leg. et det. A. G. Irwin, coll. Norwich Castle Museums; 1 f, 6.viii.2008, West Norfolk, Caudlesprings, Nymphaea / Phragmites pond [52,578°N 0,863°E], leg. et det. A. G. Irwin, coll. Norwich Castle Museums; 1 m, 10.viii.1983, West Norfolk, Thompson Common [52,527°N 0,843°E], ex Carex tussock, leg. et det. A. G. Irwin, coll. Norwich Castle Museums; 1 f, 1.viii.1985, West Norfolk, Thompson Common near old car park [52,532°N 0,848°E], leg. et det. A. G. Irwin, coll. Norwich Castle Museums.

Diagnosis. Only the two species A. cesta and A. clausseni are known within Europe and these may be distinguished using the key below. In the key of KRIVOSHEINA and MATHIS (2010) A. clausseni will run to couplet 4, where A. cesta and the Holarctic A. nigrifacies are separated. The distinction of these two species using the characters given at couplet 4 of that key is unreliable because the facial dusting of A. cesta can vary, with some specimens having a completely dusted facial carina and others with a subshining or shining facial carina. Therefore, segregation of the species using this character is not possible and reliance should be placed instead on the shape of the phallus. A. clausseni differs distinctly from A. nigrifacies in the shape of the phallus (cf KRIVOSHEINA & MATHIS 2010: 385, Figs 41, 43).

Description of male Holotype. Length about 1.7 mm. Wing length = 1.6 mm. Head height = 0.4 mm. Head black. Gena-eye ratio = 0.3 (in lateral view, genal height measured at maximum eye height).

Antenna black, light brown dusted. Arista brown, with short setulae only. All om- matidia of about same size, all over with scattered, distinct ommatrichia. Eye height-length ratio = 0.9 (in lateral view, maximum eye height / maximum eye length). Ocelli almost forming an isosceles triangle. Frons shining black, with ocellar triangle, anterior margin of frons and fronto-orbital plate slightly dusted. Frontal triangle not delimited. Frons polished, fronto-orbital plate slightly wrinkled. Face with small and barely projecting facial view. Abbreviations: ce = cercus, ep = epandrium, ph = phallus, pha = phallus apodeme tubercle. Face silver dusted with central area around facial tubercle subshining. Facial ratio = 1.5 (in frontal view, distance between the oral margin and the dorsum of the ptilinal fissure / narrowest distance between the compound eyes across the face). Clypeus black, short, slightly silver-grey dusted. Gena silver-grey dusted, black in anterior view. Occiput silver-grey dusted. Palpus black. Proboscis inconspicuous. Chaetotaxy: large ocellar seta inserted lateral to anterior ocellus; no setulae between ocelli; no postocellar seta; 1 large medial vertical seta; no paravertical seta; no postocular setae; 1 large lateroclinate frontoorbital seta; no frontal setulae; 2 inconspicuous lateral inclinate facial setae and facial ridge with 4 upcurved setae; 5-6 inconspicuous genal setae.

Thorax with brown to grey dusting and lacking any obvious setulae. Scutum and scutellum lightly covered with brown dusting, lacking any dusting patterns. Pleurae densely grey dusted. Anepisternum dorsally with scattered brown setulae. Anepisternum subshining, with posterodorsal corner shining. Anepimeron subshining, with upper third mainly shining. Chaetotaxy reduced: 1 line of minute acrostichal setulae; 0+1 dorsocentral setae, with a line 7-8 setulae which might represent additional dorsocentral setae in front of the dorsocentral seta; no prescutellar seta; no postsutural supra-alar seta; no postpronotal seta; 1 notopleural seta only; 1 postalar seta; 1 large apical and 1 small lateral scutellar seta; 1 small posterodorsal katepisternal seta; 1 small seta at posterior margin of anepisternum. Wing slightly brownish infuscated, veins light brown to black. Wing completely covered with microtrichia. Costa without setae between subcostal break and R 4+5 but with slightly elongated setulae. Alula small, with long brown setulae at hind margin. Costal Index I = 0.9 (straight line distance between the apices of R 1 and R 2+3 [S2 C] / straight line distance between the apices of R 2+3 and R 4+5 [S3 C]). Costal Index II = 2.5 (straight line distance between the apices of R 4+5 and R 2+3 [S3 C] / straight line distance between the apices of Media and R 4+5 [S4 C]). R 4+5 -vein ratio = 0.2 (straight line distance along vein R 4+5 between crossvein r-m and branch of R 4+5 and R 2+3 [S1 R 4+5] / distance apical of r-m [S2 R 4+5]). M-vein ratio = 0.5 (straight line distance along vein M between crossveins dm-cu and r-m [S1 M] / distance apical of dm-cu [S2 M]). Costa reaching apex of R 4+5 only. Radial vein R 4+5 almost straight. Haltere brownish, with black knob. Legs black, with knees and tarsi dark brown. Legs slightly brown dusted except for the shining posterior surface of hind leg. Legs with short black to golden setulae. No distinct setae on legs. Metatarsus II-tibia II ratio = 0.4 (length metatarsus 2 / length tibia 2).

Abdomen black. Lateral margins of tergites sharply creased. Tergites shining and with conspicuous pits, with brown setulae originating in the pits. Tergite III–IV ratio = 0.5 (length tergite 3 medially / length tergite 4 medially). Tergite IV–V ratio = 7.4 (length tergite 4 medially / length tergite 5 medially). Sternites not visible without preparation because lateral margins of tergites overlap ventrally. Sternites as shown at Fig. 8 . No setulae recognised on sternites. Epandrium small ( Fig. 4 ), with fine setulae only. Cercus small, only slightly longer than depth of epandrium anterior to it. No recognisable surstylus-like structure. Subepandrial plate not recognised. Hypandrium represented by an elongated plate with its lateral edges connected by a semicircular bridge ( Fig. 9 ). Gonite with broad base that is fused with hypandrium, and with a pointed and downcurved tip. Phallus apodeme with distinct angle ( Fig. 5 ). Phallus U-shaped at base, distiphallus with folds that reach from base to tip. [Male postabdomen and sternites are described based on 2 dissected paratypes.].

Variability. Knob of haltere may be brown. Legs may be completely black.

Female. Except for the postabdomen, there are no obvious differences between sexes.

Figures

Fig. 1. Habitus of Axysta clausseni (holotype)

Figs 2–5. Terminalia of European Axysta: 2 = epandrium A. cesta, dorsal view; 3 = phallus A. cesta, lateral view; 4: epandrium A. clausseni, dorsal view; 5 = phallus A. clausseni, lateral

Figs 6–7. Distribution of microtrichia on anepisternum and anepimeron, lateral view: 6 = A. cesta; 7 = A. clausseni. Abbreviations: anepm = anepimeron, aneps = anepisternum

Figs 8–9. Axysta clausseni, male: 8 = sternites 1–5; 9 = postgonite and hypandrium, lateral view.Abbreviations: hyb = hypandrium bridge, hyp = hypandrium plate, pgo = postgonite, S1 = sternite 1, S5 = sternite 5