The genus Phantolabis (Diptera: Limoniidae) new to the Palearctic: description of a new species and re-definition of the genus

A new crane fly species from the genus Phantolabis Alexander, 1956, active in the cold season and previously known by a single, eastern Nearctic species, is described from Primorsky Krai of the Russian Far East. A revised definition of the genus is given.

The fauna of Limoniidae of the Russian Far East has been well studied (Savchenko 1983(Savchenko , 1989Savchenko & Krivolutskaya 1976;Pilipenko & Sidorenko 2006a, 2006bPilipenko 2009) and currently includes 56 genera and 415 species (Oosterbroek 2020). Nevertheless, in 2006, a peculiar crane fly species was noticed among the material collected earlier by Evgeniy A. Makarchenko (Russian Academy of Sciences, Far East Branch, Federal Scientific Center of the East Asia Terrestrial Biodiversity). In the early spring of 2015, Dmitry E. Shcherbakov (Borissiak Paleontological Institute, Russian Academy of Sciences) obtained another male of this species from a Malaise trap in the Sikhote-Alin Nature Reserve (Fig. 4), which indicated a wider distribution of this species in Primorsky Krai (Fig. 5). Due to its unusual morphology, which precluded its placement into any known Palearctic limoniid genus, its description was postponed.
A recent publication by Bouchard & Gelhaus (2019) provided a redescription and biological data for the little-known Nearctic genus Phantolabis Alexander, 1956 with a single species, Phantolabis lacustris Alexander, 1938, and made it clear that the Russian specimens represented a new species of the same genus.

Material and methods
The examined material is deposited at the following collections: The holotype and other specimens are preserved in plastic tubes in 70% ethanol. Two males from the type series were dried and mounted in the course of the study. Colors are described from the dry-mounted specimens. Genitalia of two males and one female were macerated in warm 10% KOH for about one hour to remove soft tissues, then rinsed in distilled water. Cleared parts are preserved in glycerol-filled microvials together with the rest of the specimen, in ethanol-filled tubes or pinned below the specimen. The material was studied with an Olympus SZ61 stereo microscope. A Nikon d7000 digital camera, equipped with a Tamron 70-300/4-5,6 and an EL-Nikkor 50/2,8 lenses or a Mitutoyo M Plan Apo 10X and an Olympus ULWD MS Plan 20X microscope objective lenses and controlled by the Helicon Remote ver. 2.6.5.w (https://www.photo-soft.ru/) software, were used to capture stacked images, which were then combined using the Helicon Focus ver. 6.7.1.Pro software (Kozub et al. 2000(Kozub et al. -2013. The resulting images were processed in Adobe Photoshop CS2. Morphological terminology generally follows McAlpine et al. (1981), except that the notation of wing veins follows The Manual of Afrotropical Diptera (Cumming & Wood 2017) and the terminology of male terminalia is changed according to Ribeiro (2006Ribeiro ( , 2008: lobe of gonostylus = inner gonostylus, clasper of gonostylus = outer gonostylus. The general distribution of species is given according to Oosterbroek (2020). Genus Phantolabis Alexander, 1956 Type species Erioptera lacustris Alexander, 1938.

Diagnosis
Small (wing length not exceeding 5.0 mm), greyish dark brown species; antenna short, with 11-12 segments, apical flagellomere elongate, formed by fused distal segments. All legs with a short third tarsomere and tarsal claws inserted subapically. Mid and hind tarsi with shortened first and second segments, third tarsomere modified, with keel-like edge. Wings wide with wide anal angle, veins almost without microtrichia, veins R, CuA and A 1 thickened, arculus poorly visible, cell R 3 long, with short R 2+3+4 , discal cell open, crossvein m-m absent. Hypopygium not inverted, gonocoxites massive, lobe of gonostylus well developed, with short flat teeth, clasper of gonostylus rod-like, short and inconspicuous. Interbase slender, curved, and needle-like, lateral processes of aedeagal sheath (= parameres) absent. Aedeagus long, straight, thin, divided apically into two or three rods.

Diagnosis
Differs from P. lacustris by wing venation, structure of male genitalia and ovipositor. Wings entirely brownish, crossvein r-m connecting to Rs near wing midlength, apex of R3 bent to costal margin, apical part of vein CuP strongly curving toward wing margin, A 1 straight, noticeably thickened basally. Gonocoxites massive, with large ventromesal protrusion basally and ventral protrusion apically; lobe of gonostylus well developed, apically with 4-5 small teeth on inner surface; clasper of gonostylus small, situated at base of lobe of gonostylus, plate-like, each with thin apical process; aedeagus relatively thin, long and straight, apically bent upward and divided into two short rods.

Etymology
The specific Latin epithet 'glacialis' refers to the discovery of this species on ice.
Legs (Fig. 1E). Coxae and trochanters light brown, femora light brown, tibiae brown without spurs, tarsomeres yellowish brown. Legs covered with very short, semi-erect brown setae. Mid tarsus with shortened first and second segments, third tarsomere short with rounded outgrowth on outer lateral side. Tarsal claws inserted subapically, claw simple, without additional spines, arolium absent.
Wings (Fig. 1D). Wide, brownish, sometimes darkened along CuA, veins brownish, almost without macrotrichia. Macrotrichia on wing membrane absent. Venation: arculus absent; Sc short, ending about level with midlength of Rs, stigma indistinct, but costal margin after Sc thickened, sc-r indistinct (if present then close to Sc tip); origin of Rs approximately level with apex of A 1 ; R 1 long, apex of R 3 bent to costal margin; bases of cells r 1 and r 3 at same level. Veins r-m and m-cu shifted to mid-wing, r-m connecting to Rs (not to R 4+5 as usual) closer to its middle. Discal cell very long and open due to absence of m-m. Apical part of CuP strongly bent toward wing margin, A 1 straight, noticeably thickened basally; anal angle wide, posterior margin widely rounded. Haltere with knob yellowish white. abdoMen (Fig. 1A). Generally light brown, grey pruinose, covered with rather long, erect, yellow setae; tergites brownish yellow, grey pruinose, lateral and medial stripes missing, posterior margins of tergites greyish. Sternites yellowish grey.
HypopygiuM ( Fig. 2A-H). Dark brown, grey pruinose. Tergite IX transverse with shallow U-shaped notch. Gonocoxites massive, covered with spike-shaped setae directed laterally, with large ventromesal protrusions basally and ventral protrusions at apex (Fig. 2D). One pair of terminal gonostyli well developed, lobes of gonostyli (Fig. 2G-H), each shaped as triangular-rounded plate, apically with 4-5 small teeth on inner surface. Claspers of gonostyli strongly reduced, poorly visible, each situated at base of adjacent lobe of gonostylus, shaped as small plate, tightly attached to the gonostylus with thin process directed inward. Distal portion of interbase (Fig. 2E-F) simple, appearing as slender  rod gradually narrowing to acute point, basal portions of interbases merge together medially to form separate crescent-shaped plate above aedeagus, referred to here as interbasal plate (ip). Lateral apodeme of paramere poorly developed. Lateral processes of aedeagal sheath absent. Aedeagus relatively thin, long and straight, protruding beyond apices of interbases and reaching approximately to midlength of gonocoxites, apically bent upward and divided into two short rods.

Elevation
Specimens were collected at altitudes from approximately 25 to 600 m a.s.l.

Period of activity
Adults fly in March-April.

Discussion
A male of the Nearctic species Phantolabis lacustris was described by Alexander (1938) and assigned to the subgenus Psiloconopa Zetterstedt, 1838 of the genus Erioptera Meigen, 1803. In 1956, this species was transferred to the genus Cryptolabis Osten Sacken, 1860 and a new, monotypic subgenus Phantolabis (Alexander 1956) was created. In a generic key (Alexander & Byers 1981) it was listed as the genus Phantolabis. In its adult and especially larval (Bouchard & Gelhaus 2019) characters this genus is close to Hesperoconopa Alexander, 1948(Alexander 1948, 1952, 1962, 1967, 1976Savchenko 1980). The Nearctic species of Hesperoconopa have well-developed merons (Bouchard & Gelhaus 2019), while H. acutistyla Savchenko, 1980 from South Kurils has a reduced meron and tuberculate pits indistinct (Savchenko 1980). In Phantolabis the meron is not separated by a suture from the katepimeron and fuses with the lower portion of the katepimeron to form a composite region referred to by Crampton (1943) as meropleurite or meropleuron. Phantolabis differs in some adult features, such as the antenna with 11-12 segments, the veins almost without microtrichia, and the structure of legs. The hypopygium of Phantolabis differs in the clasper of the gonostylus being strongly reduced and poorly visible. One pair of well-developed interbases are present. The lateral processes of the aedeagal sheath (inner gonapophyses or apophyses according to Alexander) are absent. Aedeagus divided apically into two or three rods. Hesperoconopa (Alexander 1948) has a pair of outer gonostyli (= claspers of gonostyli). It also has well-developed interbases and lateral processes of the aedeagal sheath (or parameres), aedeagus not divided apically. A characteristic biological feature of Phantolabis is the appearance of adults at low temperatures at river banks during the early spring (Bouchard & Gelhaus 2019).
Phantolabis glacialis sp. nov. is similar to P. lacustris in its general appearance but differs by wing color and venation as well as structures of the male and female terminalia. The wings of both sexes of P. glacialis sp. nov. are entirely brownish, while the wings of females of P. lacustris have lighter areas in cells r 1 , r, and m, and in apical wing cells r 3 to m 4 (Bouchard & Gelhaus 2019). The new species also differs in some venation characters, such as vein r-m connecting to Rs some distance before its fork, apex of R 3 bent to the costal margin, and CuP strongly curving toward the wing margin.
The hypopygium of P. glacialis sp. nov. differs by the lobes of the gonostyli apically carrying 4-5 small teeth on the inner surface, in contrast to "single row of 12-17 short flat teeth along dorsal margin" in P. lacustris. The aedeagus of P. glacialis sp. nov. is simple, relatively thin, long and straight, apically bent upward and divided into two short rods, while in P. lacustris it is divided from its midlength into 3 closely appressed rods with separated apices (Bouchard & Gelhaus 2019). The ovipositor of female P. glacialis sp. nov. differs from that of P. lacustris by the longer cercus, narrow tergite VIII, and two spermathecae (three in P. lacustris).
The larvae of the new species most probably develop in sandy to gravelly bottomed streams (Fig. 4), like those of P. lacustris. The adults, too, appear at low temperatures at the banks of small rivers during early spring and possibly during winter thaws. According to the collector Evgeniy A. Makarchenko (pers. com.), the males and females formed aggregations on the underside of ice (as reflected in the species name) hanging over the water. The morphological and ecological features of P. glacialis sp. nov. are similar to those of P. lacustris (Bouchard & Gelhaus 2019), indicating that the new species is probably also capable of skating and does not fly. Nevertheless, its flying and skating capabilities both require confirmation by further studies. Phantolabis lacustris is currently known from the central and eastern parts of the United States and Canada (Bouchard & Gelhaus 2019). The discovery of the new species in the East Palaearctic suggests that this genus had a wider distribution in the Nearctic in the past and may have crossed Beringia, as also did the genus Hesperoconopa (Savchenko 1980).