Collessomma gnoma, Lukashevich & Blagoderov, 2020

Lukashevich, Elena D. & Blagoderov, Vladimir A., 2020, Review of Mesozoic Perissommatidae (Insecta: Diptera), Zootaxa 4718 (4), pp. 481-496 : 488

Collessomma gnoma sp. nov.

( Figures 4D, E , 5 )

urn:lsid:zoobank.org:act:C13DDF80-EB17-4C0F-B0C3-26699D769C4C

Holotype. PIN, No. 5026/201, part and counterpart, well-preserved impression of a male.

Type Horizon and Locality. Khasurty; Western Transbaikalia, Buryatia, Zakamensk District, middle reaches of the River Khasurty, 10 km south of the village of Tsakir (50°21’N 103°37’E); lower part of Gusinoe Ozero Group, Lower Cretaceous.

Etymology. The species epithet refers to Latin gnomus —diminutive, fabled being or dwarf.

Description. Tiny flies. Thorax dark brown, darker than abdomen and legs. Segments of antenna 4–10 transverse (wider than long). Sc ends on R, proximad of R 1 base; Rs stem subequal to basal segment of R 5. R 4 twice as long as R 3. Coxa and femur pubescent with long thin trichia, longer than width of femur. Shape of male ninth tergite not discernible, but it’s length slightly shorter than gonocoxites. Male hypopygium probably dorsoflexed, densely pubescent with long setae; gonostyli shorter than gonocoxites, widest at midlength and tapering towards apex. Female cerci elongated, longer than sternite VII and VIII combined.

Measurements (mm). Body length 2.1–3.3 (holotype 2.9), head length/width 0.3/0.4 (female), 0.4/0.7 (male, holotype), diameter 0.6 (male), antenna length 0.5 in both sexes, thorax length 0.7–1.0 (holotype 0.9), abdomen length 1.5–2.0 (holotype 1.8), wing 2.5–3.1 (holotype 3.0), halter 0.5, fore leg femur 0.45–0.6 (holotype 0.6), tibia 0.45–0.6, tarsus 0.5–0.7 with first tarsomere 0.3, female cerci length 0.1.

Material. Besides holotype, paratypes PIN, No. 5026/203±, 5026/207±, 5026/1800±, 5340/2984± (sex unknown), PIN, No. 5340/986±, 5340/2981± (females) and PIN, No. 5340/2982± (male).

Remarks. Some extant members of Perissomma also distinct from each other in the size of the male ninth tergite ( Colless 1969).

In the holotype of C. gnoma gen. et sp. nov. the apical portion of the abdomen is bent onto the dorsal side ( Fig. 5D ). Probably the dorsoflexion is facultative because it is absent in another male of Collessomma , holotype of the type species ( Fig. 2A ). Unfortunately, now we have only two undoubted males with termimalia preserved in our disposal, and it is not enough for conclusions—it may be a disarticulated part. Dorsoflexion is widely distributed among Diptera but was not recorded in Perissommatidae before.

Figures

FIGURE 2. Male of Collessomma sibirica gen. et sp. nov. A–E. holotype PIN No. 5340/1681. A. Total view. B. Terminalia. C, D. Head, dorsal and ventral view. E.Anterior part of wing with pterostigma. F. PIN No. 5026/1558, head with facets of different size. Scale bars 1 mm (A), 200 μm (B–F).

FIGURE 4. Collessomma gen. nov. A–C. C. sibirica gen. et sp. nov. A, B. Male? PIN No. 5026/206, wing and tarsus. C. Holotype PIN No. 5340/1681, male terminalia. D, E. C. gnoma gen. et sp. nov. Holotype PIN No. 5026/201, wing and male terminalia. F, G. C. mongolica gen. et sp. nov. F. Paratype PIN No. 3559/4154, wing. G. Holotype PIN No. 3559/10039, female terminalia.Abbreviations: aed, aedeagus; cerc, cerci; gst, gonostylus; gx, gonocoxite; TG6–9, tergites 6–9; ST6-8, sternites 6–8. Scale bars 1 mm (A, F), 500 μm (D), 200 μm (C, E, G), 100 μm (B).

FIGURE 5. C.gnoma gen. et sp. nov. A–C. Paratype PIN No. 5340/2982, male. A, B. Ventral and dorsal view of head (part and counterpart). C. Leg. D, E. Holotype PIN No. 5026/201, male, total view and terminalia. F–H. Paratype PIN No. 5340/2981, female. F. Antenna. G. Cerci. H. Total view. Scale bars 200 μm (A, B, C, E, F, G), 1 mm (D, H).