Omalium longicorne Luze, 1906

Shavrin, Alexey V., 2025, Review of the genus Omalium Gravenhorst, 1802 (Coleoptera: Staphylinidae: Omaliinae: Omaliini) of Siberia and Far Eastern Russia, with notes on some species from Mongolia and Japan, Zootaxa 5646 (2), pp. 199-235 : 202-207

3.2.1.1. Omalium longicorne Luze, 1906

( Figs 1 , 4–5 , 17 , 20 )

Omalium longicorne Luze, 1906: 543 .

Omalium (Omalium) longicorne : Bernhauer & Schubert 1910: 54.

Type material examined. Holotype ♂ ( Fig. 1 ; dissected prior to the present study): ‘ Shangai | Leder 1892.’ <handwritten in black>, ‘sulcifrons Epp | Norde Mongol.’ <handwritten in black>, ‘c. Eppelsh. | Steind. d.’ <printed>, ‘longicorne m. [handwritten in black] | Type. [handwritten in black] | det. Luze [underlined]’ <printed>, ‘TYPUS’ <red, printed>, ‘ Omalium | longicorne Luze, 1906 | Shavrin A.V. det. 2025’ <printed> (NMW).

Material examined. RUSSIA: AMUR AREA: 1 ♂: Selemdzhinskiy District, Norskiy Nature Reserve , Nora River basin near Meunskiy cordon. 260 m a.s.l., mosses, leaf litter, plant debris among Carex tussocks and under Spiraea spp. and Vaccinium uliginosum near small frozen rill on mari near foot of SE slope of Ust’-Meunskaya Mt. 21.09.2008. E.M. Veselova & A.B. Ryvkin leg. (cSh) .

Redescription. Measurements (n=4): HW: 0.53–0.62; HL: 0.41–0.47; OL: 0.17–0.18; TL: 0.07; AL (holotype): 1.40; PL: 0.47–0.57; PWmax: 0.65–0.75; PWmin: 0.57–0.71; ESL: 0.88–1.07; EW: 0.81–1.07; MTbL (holotype): 0.57; MTrL (holotype): 0.27 (MTrL 1–4: 0.12; MTrL 5: 0.15); AW: 0.90–1.20; AedL: 0.68–0.81; BL: 3.06–4.10 (holotype: 3.80).

Habitus as in Fig. 1 . Body yellowish-brown to reddish-brown, with paler lateral and basal parts of pronotum and elytra in two specimens; maxillary palpomeres and antennae brown, with paler antennomeres 1–4; mouthparts, legs and paratergites yellow-brown (tarsi slightly paler). Punctation of head dense, moderately coarse and deep, denser in middle, slightly sparser between anteocellar foveae, finer and sparser on posterior parts of infraorbital portions; neck with sparse or dense, moderately fine punctation; punctation of pronotum dense and relatively fine, sparser in medioapical and mediobasal (holotype) or in middle portions, sparser in lateroapical and usually larger in laterobasal portions; scutellum without punctures; punctation of elytra dense, about as that on pronotum, but slightly larger and deeper, finer and sparser around scutellum and along suture and denser, coarser in lateral and apical portions; abdominal tergites with indisinct, sparse and fine punctation. Anterior portion of clypeus with distinct transverse microsculpture, laterobasal parts of clypeus with traces of fine longitudinal meshes, middle portion without or with fine subdiagonal microreticulation, each mediodorsal part of infraorbital portion near eye with fine longitudinal meshes; medioapical part of neck without or with fine transverse microsculpture; pronotum and elytra without sculpture; scutellum with fine indistinct isodiametric or transverse meshes; abdominal tergites with dense transverse or isodiametric microreticulation. Anterior portion of clypeus with several erect and moderately long setae (specimen from Amur Area with additional long erect setae in each mediolateral part of clypeus and mediobasal part of infraorbital portion); lateral portions of pronotum with several short suberect setae; abdominal tergites with fine, sparse and short setation; posterior margin of pronotum with row of very short cuticular fringe visible in the holotype.

Head 1.2–1.3 times as broad as long, somewhat flattened or slightly elevated in middle, with relatively broad clypeus and strongly convex and slightly explanate supra-antennal elevations, and with shallow to moderately deep and wide elongate anteriomedian depressions, reaching about level of anterior third of eyes; each posteriolateral margin of clypeus diagonally stretching posteriad toward level of middle or posterior third of eye. Mediodorsal surface with distinct diagonal elevations on lateral portions of clypeus, with elongate narrow elevation (indistinct in holotype) along each infraorbital portion near margin of eye and several shorter indistinct wrinkles between it and mediodorsal margin of eye. Anteocellar foveae short, suboval or slightly elogate, very deep, not or slightly convergent latero-apicad toward level of posterior third of eyes. Temples moderately convex, more than twice as long as longitudinal length of eye, gradually narrowed posteriad. Nuchal constriction present, narrow but moderately deep. Eyes large and convex. Ocelli moderately small, indistinct, located significantly behind level of posterior margins of eye; distance between ocelli short, more than one and a half times as long as distance between ocellus and posterior margin of eye. Maxillary palpi moderately long, palpomere 4 (apical) slightly more than three times as long as slightly elongate penultimate segment, from widest middle gradually narrowed toward subacute apex. Antenna reaching basal portion of elytra when reclined, with distinctly elongate antennomeres, gradually broadened apicad; basal antennomere wide and robust, about three times as long as broad, antennomere 2 about twice shorter and narrower than basal segment, 3 slightly narrower and distinctly longer than 2, 4–5 shorter than 3, 6–7 slightly longer and broader than 5, 8–10 distinctly broader than 7, apical antennomere slightly longer than preceding segment, from about middle gradually narrowed toward rounded or subacute apex.

Pronotum slightly convex, 1.3 times as broad as long, 1.2 times as broad as head, from widest middle gradually narrowed both anteriad and posteriad or slightly more narrowed posteriad toward obtuse hind angles. Apical angles broadely widened, not or indistinctly protruded anteriad. Anterior margin straight or slightly rounded, distinctly shorter than slightly rounded posterior margin. Lateral portions narrowly margined, slightly explanate in lateroapical portion, each with deep and wide elongate impressions slightly behind middle. Surface of disc with two elongate, shallow or moderately deep longitudinal depressions, significantly broadened basad, with small and shallow medioapical depression; each lateroapical portion with curved narrow elevation (invisible in holotype), reaching middle of pronotum; surface between all pronotal depressions distinctly elevated. Medioapical portion with irregular and sometimes indistinct diagonal elevations between punctures.

Elytra slightly longer or about as broad as long, 1.8 times as long as pronotum, somewhat parallel-sided or distinctly broadened posteriad; lateral portions narrowly impressed, slightly explanate in middle; hind margins somewhat straight or rounded. Dorsal surface of each elytron without or with strong irregular diagonal elevations between punctures. Hind wings fully developed.

Metatarsi about twice shorter than metatibia.

Abdomen convex, slightly broader than elytra, with two small oval wing-folding patches in middle of abdominal tergite IV and narrow palisade fringe on apical margin of abdominal tergite VII.

Male. Posterior margin of abdominal tergite VIII straight. Posterior margin of abdominal sternite VIII rounded. Aedeagus with significantly broadened and relatively short basal portion, slightly narrowed toward middle; median lobe wide and short, with widely rounded apex, with small indistinct apical excision; mediolateral portions with short sclerotized accessory plates, curved latero-apicad, each rounded apically; parameres narrow, significantly shorter than apex of median lobe, slightly curved in preapical portions, each with relatively narrowed apex with two long and two short apocal setae; internal sac wide and long, with field of large spines in apical and paired oval structures in basal portions ( Fig. 4 ). Lateral aspect of the aedeagus as in Fig. 5 ; apical portion of median lobe slightly broadened, with rounded apex, slightly crenulated ventroapically.

Female. Posterior margin of abdominal tergite VIII straight. Posterior margin of abdominal sternite VIII slightly rounded. Accessory sclerite short, from widest basal portion gradually narrowed toward small rounded apex ( Fig. 17 ). Spermatheca not recognized.

Comparative notes. Based on the general shape of the aedeagus, O. longicorne is related to the amplissimum group, recently erected by Shavrin (2023) for two species from the Himalayan region. Regarding the general shape of the aedeagus, with narrowed parameres and the presence of medioapical excision of the median lobe, O. longicorne is somewhat similar to the Nepalese O. bilobum Shavrin, 2023 , but the median lobe of O. longicorne is slightly longer and narrower, with significantly less pronounced excision, less curved shorter parameres and with different details of the internal sac. It can be distinguished from both species by the longer body, elongate antennomeres 4–10, the shape of the pronotum widest in middle, shorter elytra, different morphology of the aedeagus, and the shape of the female accessory sclerite. Also see the key below.

Distribution. North-eastern Mongolia, Russia (Buryatia, Amur Area) ( Fig. 20 ).

Bionomics. Specimens were collected at elevations from 260 to 350 m a.s.l. A specimen from Buryatia was collected in horse dung ( Voincov 2010). A specimen from Amur Area was collected by sifting mosses and litter.

Remarks. Omalium longicorne was originally described from “Nördliche Mongolei (Shangai [=Khangai Mountains])” without providing of the exact locality. It was recorded from southern Buryatia ( Voincov 2010; Shavrin 2010). I decided to redescribe this species using additional specimens provided in the listed papers above. The habitus, the aedeagus and the female accessory sclerite are illustrated for the first time.

It is here recorded from Amur Area for the first time.

Figures

FIGURE 20. Distribution of Omalium longicorne in eastern Palaearctic region.

FIGURES 1–3. Habitus of Omalium: 1—O. longicorne (holotype), 2—O. golovatchi (holotype), 3—O. oxyacanthae (Russia: Khamar-Daban Mts.). Scale bar: 1.0 mm.

FIGURES 4–9. Aedeagus of Omalium (Figs 4–5—O. longicorne (Russia: Amur Area, Norskiy Nature Reserve), Figs 6–7—O. golovatchi (paratype), 8–9—O. diffine (Japan: Tokyo)): 4, 6, 8—aedeagus, parameral view, 5, 7, 9—aedeagus, lateral view. Scale bar: 0.1 mm.

FIGURES 10–19. Female accessory sclerite (Figs 10, 12, 14–19) and spermatheca (Figs 11, 13) of Omalium: 10–11—O. curtipenne, 12–13—O. diffine, 14—O. golovatchi, 15—O. japonicum, 16—O. kurilicum, 17—O. longicorne, 18—O. strigicolle, 19—O. subsolanum. Scale bar: 0.1 mm.