Burmella, Godunko & Martynov & Staniczek, 2021

Godunko, Roman J., Martynov, Alexander V. & Staniczek, Arnold H., 2021, First fossil record of the mayfly family Vietnamellidae (Insecta, Ephemeroptera) from Burmese Amber confirms its Oriental origin and gives new insights into its evolution, ZooKeys 1036, pp. 99-120 : 99

Genus Burmella gen. nov. Figures 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , Table 1

Type species.

Burmella paucivenosa sp. nov.

Derivation of name.

The generic name of female gender is a composition of " Burmar " as an ancient term for Myanmar, combined with " ella ", a common ending of generic names in mayflies, and especially so within Ephemerelloidea .

Diagnosis.

Adults of Burmella gen. nov. differ from other mayfly genera by the following combination of features: forewings (a) with small number of cross veins; (b) pterostigma with simple veins, not anastomosed; (c) CuP smoothly curved towards wing base; (d) two secondary bifurcate veins in cubital field; (e) at least several free marginal intercalaries along ventral margin; hind wings (f) strongly rounded, small, as long as 0.08-0.14 of forewing length; (g) small number of cross veins; (h) triad RS present or absent; no MA and MP triads; (i) no secondary branches of cubital veins; (j) costal process developed, rounded apically, situated centrally; abdomen (k) with vestigial gill sockets recognizable at least on segments II-VI; genitalia (l) with large median projection of styliger plate, widely rounded apically; (m) three distal segments of forceps strongly elongated and slender; segment II longest, 5 × as long as segment III; segments III and IV approximately of equal length; segment IV expanding apically; (n) penis lobes widely separated by V-shaped cleft; (o) no trace of paracercus. Additionally, in female (p) anterior part of eyes covered by anterolaterally expanded clypeal shield.

Subimago and larva unknown.

Species composition.

Burmella paucivenosa sp. nov. (SMNS; BU-179); Burmella clypeata sp. nov. (SMNS; BU-321).

Locality and horizon.

Hukawng Valley, Kachin State, Myanmar (Burma); Cenomanian, mid-Cretaceous.

Figures

Figure 1. Burmella paucivenosa sp. nov., male imago, holotype, general lateral view A left side of body B right side of body. Scale bars: 2 mm.

Figure 2. Burmella paucivenosa sp. nov., male imago, holotype A head, right lateral view B compound eye, left lateral view C head and thorax, left lateral view D mesothorax, left lateral view. Blue line - border between portions of compound eye, da - damaged area, lp - lower portion, LPs and red line - lateroparapsidal suture, MNs and green line - mesonotal suture, MPs and yellow line - medioparapsidal suture, up - upper portion. Scale bars: 0.5 mm (A, C); 0.2 mm (B, D).

Figure 3. Burmella paucivenosa sp. nov., male imago, holotype A, B tarsus of right middle leg C right middle leg D left hind leg. I-V - tarsal segments, pts - patellotibial suture. Scale bars: 0.1 mm (A, B); 0.5 mm (C); 0.2 mm (D).

Figure 4. Burmella paucivenosa sp. nov., male imago, holotype A right and left wings position in amber B right forewing venation and size ratio of fore and hind wings. Scale bars: 1 mm.

Figure 5. Burmella paucivenosa sp. nov., male imago, holotype A right hind wing in amber B right hind wing venation. Scale bars: 0.2 mm.

Figure 6. Burmella paucivenosa sp. nov., male imago, holotype A abdomen, left lateral view B abdominal segments III-VII, lateral view C, D genitalia, ventrolateral view. III-VII - numbers of segments, white arrows mark remnants of gill sockets, pink area - penis lobes, light blue area - gonobasis (styliger plate), brown area styliger segment I, yellow area - styliger segment II, light green area - styliger segment III, purple area - styliger segment IV. Scale bars: 1 mm (A); 0.5 mm (B); 0.2 mm (C, D).

Figure 7. Burmella clypeata sp. nov., female imago, holotype A general dorsal view B general ventral view C, D head, dorsal view E head and thorax, dorsal view. BA - basal sclerite (basalare), LPs and red line - lateroparapsidal suture, MNs and green line - mesonotal suture, MPs and yellow line - medioparapsidal suture, rc - right cercus. Scale bars: 2 mm (A, B); 0.2 mm (C, D); 0.5 mm (E).

Figure 8. Burmella clypeata sp. nov., female imago, holotype A tarsus of left hind leg B tarsus of right hind leg C left forewing in amber D left forewing venation and size ratio of left fore- and right hind wings E distal part of left forewing F preserved basal part of right forewing. I-V - tarsal segments, ci - basally connected intercalary vein, fi - basally free intercalary vein. Scale bars: 0.1 mm (A, B); 1 mm (C, D); 0.5 mm (E, F).

Figure 9. Burmella clypeata sp. nov., female imago, holotype A right hind wing, dorsal view B right hind wing, ventral view C right hind wing venation. Scale bars: 0.2 mm (A, B); 0.5 mm (C).

Figure 10. Burmella clypeata sp. nov., female imago, holotype A body, ventral view B, C apical part of abdomen, ventral view D basal segments of abdomen, dorsal view. I-III and V-IX - numbers of abdominal segments, gsr - remnant of gill socket, pp - paraproct plate. Scale bars: 1 mm (A); 0.5 mm (B-D).