Omalium bilobum, Shavrin, 2023

Shavrin, Alexey V., 2023, A revision of the genus Omalium Gravenhorst, 1802 (Coleoptera: Staphylinidae: Omaliinae) of the Himalayan region, Zootaxa 5369 (2), pp. 151-206 : 164-167

3.2.2.2.2. Omalium bilobum sp. n.

( Figs 12 , 25 , 30–33 )

Type material. Holotype ♁ (dissected; apical antennomere of left antenna missing): ‘E. NEPAL: KOSI | Forêt N-E Kuwapani | 2250 m, 24.IV.[19]84 | [I.] Löbl - [A.] Smetana’ <printed >, ‘ HOLOTYPE | Omalium | bilobum sp. n. | Shavrin A.V. des. 2023’ <red, printed> (MHNG).

Paratype ♀ ( Fig. 25 ; dissected): same data as the holotype, with additional red printed label : ‘ PARATYPE | Omalium | bilobum sp. n. | Shavrin A.V. des. 2023’ (MHNG).

Description. Measurements (n=2): HW: 0.47–0.51; HL: 0.37; OL: 0.15; TL: 0.07–0.09; AL (holotype): 0.93; PL: 0.37–0.40; PWmax: 0.60–0.62; PWmin: 0.56–0.58; ESL: 0.77–0.83; EW: 0.84–0.89; MTbL (holotype): 0.46; MTrL (holotype): 0.17 (MTrL 1–4: 0.07; MTrL 5: 0.10); AW: 0.80–0.86; AedL: 0.45; BL: 2.80 (holotype)–2.97.

Habitus as in Fig. 25 . Body reddish-brown, with distinctly darker head and abdomen, and slightly paler lateral portions of pronotum and middle portions of elytra; antennomeres 6–11 brown; mouthparts, antennomeres 1–5 and legs yellowish. Punctation of head dense and moderately deep, distinctly sparser on clypeus and denser, slightly larger and deeper in middle and infraorbital portions, interstices between punctures in middle as broad as two to three nearest punctures; nuchal constriction with moderately sparse and large punctation; punctation of pronotum dense, markedly larger than that on head, slightly sparser on lateral and mediobasal portions; punctation of elytra dense, slightly coarser and deeper than that on pronotum, denser and finer in parascutellar portion and sparser in middle portion of each elytron. Head without microsculpture except of anterior portion of clypeus with distinct transverse microreticulation; pronotum and elytra without sculpture; scutellum with fine isodiametric meshes.

Head 1.2–1.3 times as broad as long, with moderately broad clypeus, and slightly convex supra-antennal elevations, posteriolateral margins of clypeus stretching posteriad toward level of middle length of eyes. Anteriomedian depressions moderately shallow, reaching level of anterior margin of eyes. Middle portion between eyes and infraorbital portions slightly elevated. Surface of head between anteocellar foveae with slightly elevated interspaces between punctures; surface on basal parts of infraorbital portions with longitudinal elevations between punctures; lateral portions between posterior margins of eyes and anteocellar fovea with three relatively long and slightly elevated wrinkles.Anteocellar foveae deep, sublinear, reaching level of middle length of eyes. Temples about twice shorter than longitudianl length of eyes. Distance between ocelli slightly less than twice as long as distance between ocellus and posterior margin of eye. Antennomeres 5–10 progressively broadened apicad; antennomere 2 slightly more than twice as long as scape, 3 about as long as and slightly narrower than 2, 4 very small, distinctly longer and shorter than 3, 5 insignificantly broader than 4, 6 slightly broader than 5, 7 distinctly broader than 6, 8 distinctly broader than 7, 9–10 slightly broader than 8, apical antennomere 1.3 times as long as 10.

Pronotum 1.5–1.6 times as broad as long, 1.2 times as broad as head, widest slightly above middle, with slightly protruded apical angles. Anterior margin widely rounded. Surface of disc with two distinct and wide longitudinal depressions.

Elytra slightly broader than long, twice as long as pronotum, indistinctly broadened in posterior portion. Mediobasal surface of each elytron with diagonal elevations between punctures.

Metatarsi distinctly more than twice shorter than metatibia.

Abdomen slightly broader than elytra.

Male. Antennomeres 9–10 strongly transverse. Posterior margin of abdominal tergite VIII straight. Posterior margin of abdominal sternite VIII rounded. Aedeagus wide and short, with very wide basal portion, gradually narrowed toward middle, with moderately short median lobe, from widest basal portion strongly narrowed toward middle and from middle broadened apicad toward apex with relatively wide excision in middle of apical margin; mediolateral portion with two elongate sclerotized curved accessory plates connected with middle part of median lobe and inner sides of parameres; parameres moderately wide, curved, slightly longer than apex of median lobe, with rounded apices and with three long apical setae; internal sac moderately short and wide ( Fig. 30 ). Lateral aspect of the aedeagus as in Fig. 31 ; apical portion of median lobe strongly narrowed toward apex, with slightly crenulate apical part of inner margin ( Fig. 32 ).

Female. Antennomeres 9–10 slightly transverse. Posterior margins of abdominal tergite VIII and sternite VIII rounded. Accessory sclerite with wide basal portion and moderately wide median part ( Fig. 12 ). Spermatheca not recognized.

Comparative notes. Based on the general shape of the forebody and aedeagus, O. bilobum sp. n. is similar to O. amplissimum sp. n., from which it can be distinguished by narrower antennomeres 7–9, finer sculpture of the head and the pronotum, the shape of the pronotum widest slightly above middle, with apical angles slightly protruded anteriad, the slightly broader and shorter elytra, the shape of the apical margin of the median lobe with distinct wide apical excision, shorter and narrower parameres, slightly longer than apex of the median lobe, and the morphology of the internal sac. Omalium bilobum sp. n. differs from all known species of the genus by the presence of the wide excision on apex of the median lobe.

Distribution. Omalium bilobum sp. n. is known only from the type locality in eastern part of Nepal ( Fig. 33 ).

Etymology. The specific epithet is the Latin adjective bilobus, - a, - um (with two lobes). It alludes to the shape of th apical portion of the median lobe diveded into two lobes.

Bionomics. Specimens were taken by sifting rotten branches and moss below a dead tree at elevation 2250 m a.s.l.

Figures

FIGURE 33. Distribution of Omalium in the Himalayan region: O. bilobum sp. n. (circle), O. marginatum (squares), O. altivagans sp. n. (triangle), O. humerale (diamond).

FIGURES 8–18. Female accessory sclerite (Figs 8, 10–16, 18) and spermatheca (Figs 9, 17) of Omalium: 8–9—O. acutangulum, 10—O. amicorum, 11—O. amplissimum, 12—O. bilobum, 13—O. alticola, 14—O.beesoni, 15—O. altivagans, 16–17—O. marginatum, 18—O. scapulare. Scale bar: 0.1 mm.

FIGURES 24–26. Habitus of Omalium: 24—O. amplissimum (paratype), 25—O. bilobum (paratype), 26—O. altivagans (Kashmir). Scale bars: 1.0 mm.

FIGURES 30–32. Aedeagus of Omalium bilobum (holotype): 30—aedeagus, parameral view, 31—aedeagus, lateral view, 32—median lobe, lateral view. Scale bar: 0.1 mm.