Collessomma gen. nov.

(Figures 2–6)

urn:lsid:zoobank.org:act: E4 CEAD 3D-3FA8-4B7A-B54F-E661FEFB6995

Type species Collessomma sibirica sp. nov.

Etymology. The generic epithet refers to Donald Henry (Don) Colless, an outstanding expert on Australian Diptera, who established the family Perissommatidae, and to the Greek term omma —eye. The name is feminine.

Diagnosis. Eyes in male holoptic, with facets of different size, veins with macrotrichia, dense on radial ones except for R 5, discal cell elongate, 1/4 wing length, CuP ending at level m-cu, anal lobe present.

Description. Antenna moniliform, rather short and stout, with 11 segments, flagellum not clearly differentiated, segments 2 and 3 (pedicel and first flagellomere) enlarged, all segments with fine setae only (Figs 2C, 5A, B, F). Ocelli probably absent. Eyes in male holoptic, with facets of different size, without disconnected zone (Figs 2C, D, F; 5A, B); in female dichopic, with facets of the same size (Fig. 6B). Mouthparts very short (Figs 2D, 5A). Mesonotum arched anterodorsally, scutellum separated from postscutum by distinct suture, metanotum very large (Figs 2A, 3A, 5H). Legs slender, with small tibial spurs, femur slightly expanded, first tarsomere longest, forth tarsomere shortest, empodium and pulvilli well-developed, narrow; pubescence of empodium and pulvilli invisible (Figs 3A, B, 4B, 5C). Wing relatively broad, longer than abdomen, with anal lobe but without alula, with numerous macrotrichia on pterostigma and on veins, denser on radial veins (Figs 2A, E, 3A, C, 4F, 5D, H, 6A, C). R 1 apex expanded; fork R 3+4 forms relatively acute angle, about 45°; crossvein r-m proximal to im and distal to m-cu; discal cell elongate, 1/4 wing length, CuP ending at level m-cu (Figs 2A, E, 3A, C, 4A, D, F, 5H, 6C). Male hypopygium narrower than VIII abdominal segment and relatively simple, not rotated, gonocoxites elongate and massive, gonostyli simple, stout; ninth tergite prominent (Figs 2B, 4C, E, 5D, E). Female terminalia with large, prominent bilobed eighth sternite, cerci prominent, well chitinized but not horny, and with numerous setae; three sclerotized spermathecae (Figs 4G, 5G, 6A).

Species included. Besides type species, C. gnoma gen. et sp. nov. from the same locality and C. mongolica gen. et sp. nov. from Lower Cretaceous of Mongolia, described below.

Remarks. Characters typical of the family are observed in the wing venation of the new genus: the costal vein extends along the entire wing, strongly thickened at the anterior and distal margins, weak but distinct along the posterior margin; the peculiar position of the pterostigma between R 1 and R 3; a forked anterior branch of Rs, R 3+4 combined with a simple posterior branch R 5; r–m connects R 5 and M 1+2; M stem very weak, fold-like, M 1+2 is forked, М 3+4 is simple; m–cu is positioned in the proximal part of the wing; CuP is distally reduced (Figs 2A, E, 3A, C, 4A, 5H, 6C). As all members of subfamily Perissommatinae Collessomma gen. nov. has short Sc not ending at C, short R 1 (about half of the wing length); R 3 distally closer to R 4 than to R 1; r-m in proximal half of wing and m–cu ending on M 3+4 (Figs 3A, 4A).

Tibial spurs are found in the new genus but they are unknown in the type genus Perissomma . In extant Perissommatidae “V-shaped suture of the tipuloid type ” present, in the new genus transverse suture on scutum present with certainty, but its shape is unclear. However, some other familial characters (coinciding with that of Perissomma) are observed in body structures: antenna moniliform, with 11 segments, flagellum not clearly differentiated, pedicel and first flagellomere enlarged (Fig. 5B), thorax with large metanotum; halters long-stemmed; legs with well-developed empodium and pulvilli (Figs 3A, B, 4B); well-developed eighth abdominal segment; male hypopygium narrower than VIII abdominal segment and relatively simple, ninth tergite prominent (Figs 2A, B, 4C).