Chaoboridae Edwards, 1920

Lukashevich, E. D., 2022, The oldest occurrence of Chaoboridae (Insecta: Diptera), Russian Entomological Journal 31 (4), pp. 417-421 : 420

Family Chaoboridae Edwards, 1920

Triassomyi a, gen.n.

TYPE SPECIES. Triassomyia shcherbakovi , sp.n .

DIAGNOSIS (only wing characters). Wing elongate, without spots. Sc short, ending near wing midlength, before r-m, Rs stem long, subequal to R 2+3 stem; wide R 2+3 fork longer than R 2+3 stem, with R 2 apex closer to R 1 than to R 3; rm in distal half of wing; M 1+2 fork long, longer than R 2+3 fork and M 1+2 stem; m-cu far from Rs origin; CuP subparallel to CuA, CuP terminating distal to Rs base and proximal to m-cu.

COMPOSITION. Type species.

COMPARISON. The new genus differs from all other members of the family in the shape of the R 2+3 fork, which is wide, with R 2 apex closer to R 1 than to R 3. A similar, wide fork R 2+3 has been recorded in Jordanobotomus and Libanoborus , but in both of these genera R 2 is very short, touching R 1 at its apex. A similar short Sc, ending near wing midlength, has been described in Rhaetomyia . Besides the shape of the R 2+3 fork, the latter genus is distinct in having a wider wing with short Rs stem and M

1+2

fork.

REMARKS. The wing venation of the new genus shows the following characters typical of the family: Sc complete, R 1 long and straight, Rs with three branches, R 2+3 forked, r-m connecting R 5 not far from base with M 1+2 stem, M with three branches, M 1+2 forked, discal cell absent, and CuP complete.

A distinct M base is found in the wing basiala of the new genus ( Figs 1–4 ). In the Triassic Bibionomorpha (sensu Shcherbakov et al., 1995, i.e. including Pachyneuroidea) a distinct M base is absent, whereas in the Triassic representatives of other nematoceran infraorders a strong convex M base between R and Cu bases occurs [ Shcherbakov et al., 1995]. Moreover, such an M base is also known in the extant Chaoboridae but is absent in the extant Axymyiidae and Perissommatidae [ Shcherbakov et al., 1995: figs 7, 9–10]. Distinct M bases, found in the holotypes of the new genus and Rhaetomyia necopinata Rohdendorf, 1962 ( Figs 4–5 ), rule out the bibionomorphan but do not contradict the chaoborid affinities of these genera.

The characteristic proximal fold along the margin of the anal lobe of the new genus ( Figs 1–4 ) is also known in Mesozoic Chaoboridae (e.g., Libanoborus and Mesocorethra Kalugina, 1993 ) and Dixidae ( Eucorethrina Kalugina, 1985 and Syndixa Lukashevich, 1996 ) [ Lukashevich, 1996a: figs 1– 2; Azar et al., 2009: fig. 6; Lukashevich, 2011: Plate 6, fig. 4]. A similar fold is found in Rhaetomyia ( Figs 5–6 ), additionally suggesting a culicomorphan affinity of the genus.

ETYMOLOGY. From “Triassic” and the Greek “ myia” (fly).

Figures

Figs 1–3. Triassomyia shcherbakovi gen. et sp.n., Madygen, Triassic; holotype: 1 — photograph; 2 — SEM, uncoated, BSE; 3 — drawing. Arrows mark the anal fold. Scale bars, 500 µm. Рис. 1–3. Triassomyia shcherbakovi gen. et sp.n., Мадыген, триас, голотип: 1 — фотографиЯ; 2 — СЭМ, беЗ напылениЯ, BSE; 3 — рисунок. Стрелки маркируют анальную складку. Длина масШтабных линеек 500 µm.

Figs 4–6. Wings of Mesozoic Chaoboridae (SEM, uncoated): 4 —Triassomyia shcherbakovi gen. et sp.n. (BSE), Madygen, Triassic; holotype; 5–6 — Rhaetomyia necopinata, Sogyuty, Jurassic, holotype; 4–5 — basiala (BSE); 6 — wing (LVSTD). Arrows mark the anal fold. Scale bars, 200 µm. Рис. 4–6. КрыльЯ меЗоЗойских Chaoboridae (СЭМ, беЗ напылениЯ): 4 — Triassomyia shcherbakovi gen. et sp.n. (BSE), Мадыген, триас, голотип; 5–6 — Rhaetomyia necopinata, Согюты, юра, голотип; 4–5 — баЗиала (BSE); 6 — крыло (LVSTD).Стрелки маркируют анальную складку. Длина масШтабных линеек 200 µm.