Omalium acutangulum, 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 : 154-158

3.2.1.2.1. Omalium acutangulum sp. n.

( Figs 1–2 , 5–9 , 19 )

Type material. Holotype ♁ (dissected): ‘ NEPAL Parbat Distr. | Ghoropani Pass N slope | 2700m 6.X.1983. [A.] Smetana & [I.] Löbl’ <printed >, ‘ HOLOTYPE | Omalium | acutangulum sp. n. | Shavrin A.V. des. 2023’ <red, printed> (MHNG).

Paratypes: 4 ♀♀ (one specimen dissected): same data as the holotype (1 ♀: cSh; 3 ♀♀: MHNG) ; 1 ♀: ‘ NEPAL, Dhaulagiri Mts. | Hile Kharka 3000–3100m | 28°29’15’’ N, 83°34’28 E, | 09.V.2009,leg. J. Schmidt’ <printed>, ‘collection | NATURKUNDE- | MUSEUM ERFURT’ <yellow, printed> (NME); 1 ♁: ‘ NEPAL Parbat Distr | S Ghoropani Pass | 2700m 9.X.1983 | [A.] Smetana & [I.] Löbl’ <printed> (cSh); 1 ♁, 1 ♀: ‘ NEPAL Parbat Distr. | Ghoropani Pass N slope | 2800m 5.X.1983 | [A.] Smetana & [I.] Löbl’ <printed> (MHNG); 1 ♁: ‘ NEPAL — Goropani For | Goropani face nord | 2750m 5.X.[19]83 | [I.] Löbl - [A.] Smetana’ <printed> (MHNG); 1 ♁: ‘ NEPAL Parbat | Distr. Ghoropani | Pass N slope | 2700m 6.X.1983 | [A.] Smetana & [I.] Löbl’ <printed> (MHNG); 1 ♁, 1 ♀: ‘ NEPAL Parbat | Distr. Ghoropani | Pass N slope | 2800m 5.X.1983 | [A.] Smetana & [I.] Löbl’ <printed> (1 ♁: cSh; 1 ♀: MHNG) ; 1 ♀: ‘ NEPAL (Prov. Bagmati) | Malemchi, 2900 m | 14.IV.[19]81 | [I.] Löbl & [A.] Smetana [steep slope near a river, sifted leaf litter ( Rhododendron , oak and chestnut)]’ <printed> (MHNG); 1 ♁ (dissected): ‘ NEPAL ( Prov. Bagmati) | Pokhare NE Barahbise | 2800 m, 2.V.[19]81 | [I.] Löbl & [A.] Smetana [oak forest with Rhododendron . sifted leaf litter, moss and dead wood]’ <printed> (MHNG). All paratypes with additional red printed label: ‘ PARATYPE | Omalium | acutangulum sp. n. | Shavrin A.V. des. 2023’.

Description. Measurements (n=15): HW: 0.49–0.60; HL: 0.37–0.45; OL: 0.12–0.14; TL: 0.11–0.12; AL (holotype): 1.02; PL: 0.35–0.50; PWmax: 0.59–0.72; PWmin: 0.48–0.65; ESL: 0.73–0.82; EW: 0.83–0.95; MTbL (holotype): 0.40; MTrL (holotype): 0.21 (MTrL 1–4: 0.09; MTrL 5: 0.12); AW: 0.77–0.90; AedL: 0.47–0.52; BL: 2.45–3.40 (holotype: 2.90).

Habitus as in Fig. 1 ; head and pronotum dorsolaterally as in Fig. 2 . Body reddish-brown, with distinctly darker head, and slightly paler supra-antennal elevations; antennomeres 6–11 brown; mouthparts, antennomeres 1–5, legs, paratergites and median portions of abdominal tergites IV–VI in some specimens yellowish; tarsi yellow. Punctation of head very dense, moderately large and deep, denser between eyes and anteocellar foveae, and finer on infraorbital portions; nuchal constriction with moderately dense and fine punctation; punctation of pronotum very dense, slightly larger and coarser in middle, sparser and finer in mediobasal and slightly larger and deeper on lateral portions; scutellum without punctures; punctation of elytra dense, distinctly larger and deeper than that on pronotum, coarser and deeper in apical half and slightly sparser along suture; abdominal tergites with indistinct, fine and sparse punctation. Forebody glossy; anterior portion of clypeus with fine transverse microreticulation, supra-antennal elevations with fine and sometimes indistinct diagonal meshes; pronotum and elytra without microsculpture; scutellum with fine isodiametric sculpture; abdominal tergites with very dense and fine isodiametric microsculpture. Anterior and lateral portions of head with several moderately long and erect setae; lateral margins of pronotum with several very short setae; abdominal tergites with moderately dense and short setation; anterior and posterior margins of pronotum with row of very short cuticular fringe.

Head 1.3 times as broad as long, with very broad clypeus and strongly convex supra-antennal elevations, with wide and deep anteriomedian depressions, reaching or slightly longer than level of anterior margin of eyes; posteriolateral margins of clypeus stretching posteriad toward level of middle or posterior third length of eyes. Dorsal surface with strong elevations in middle and on infraorbital portions; middle area between anteocellar foveae with irregular elevations between punctures, sometimes forming indistinct longitudinal wrinkles, portions between anteocellar foveae and eyes with strong elevations: diagonal between basal portions of clypeus and apical margins of anteocellar foveae, and with strong and very long four to five longitudinal elevations on infraorbital portions; portions between posterior margins of eyes and temples with two to three long wrinkles curved posterolaterad. Anteocellar foveae (grooves in front of ocelli) wide and very deep, slightly or distinctly convergent latero-apicad toward level of middle or anterior third of eyes. Temples convex, long, slightly shorter than longitudinal length of eye, slightly and gradually narrowed posteriad, each with subacute angle distinctly protruded basad; postocular ridges missing. Each lateroapical portions of nuchal constriction with narrow and moderately deep depression; medioapical part of nuchal constriction without distinct depression ( Fig. 2 ). Eyes large and convex. Ocelli moderately large and convex, located distinctly behind level of posterior margins of eyes; distance between ocelli short, more than twice as long as distance between ocellus and posterior margin of eye. Maxillary palpi moderately long, palpomere 4 (apical) about 3.5 times as long as small and slightly transverse penultimate segment, from widest basal portion gradually narrowed toward acute apex. Antenna reaching basal portion of elytra when reclined, with slightly transverse or somewhat elongate antennomeres 9–10; antennomere 3 about as long as and indistinctly narrower than 2, 4 very small, about twice shorter than 3, 5 distinctly longer than 4, 6 slightly broader than 5, 7 slightly longer and broader than 5, 8 distinctly broader than 7, 9–10 broader than 8, apical antennomere about 1.3 times as long as 10, from about middle strongly narrowed toward rounded or subacute apex.

Pronotum strongly convex, 1.4–1.6 times as broad as long, 1.2 times as broad as head, from very wide apical third slightly narrowed toward rounded apical angles and relatively strongly narrowed posteriad. Apical angles not protruded anteriad. Anterior margin widely rounded, slightly protruded anteriad. Lateral portions deeply and widely impressed, distinctly deeper in about middle. Lateral margins narrowly marginated, sometimes indistinctly crenulate. Surface of disc with two long and wide longitudinal depressions, significantly broadened basad, with very deep and wide mediobasal depression; medioapical portion with very deep and moderately wide suboval depression; each lateroapical portion with curved narrow elevation, reaching middle of pronotum; surface between all pronotal depressions strongly and widely elevated. Medioapical portion with irregular transverse or diagonal elevations between punctures.

Elytra distinctly broader than long, 1.6 times to twice as long as pronotum, from basal portion gradually broadened posteriad; lateral margins marginated; lateral portions widely impressed, sometimes with indistinctly crenulate lateral margins; hind margins somewhat straight or rounded. Dorsal surface of each elytron with strong irregular transverse or diagonal elevations between punctures, coarser in mediobasal and/or middle. Wings fully developed.

Metatarsi about twice shorter than metatibia.

Abdomen convex, slightly narrower than elytra, with two very small oval wing-folding patches (tomentose spots) in middle of abdominal tergite IV and distinct narrow palisade fringe on apical margin of abdominal tergite VII, usually with wide intersegmental membranes between abdominal tergites III–VII.

Male. Antennomeres 9–10 slightly transverse. Posterior margin of abdominal tergite VIII straight or slightly rounded. Posterior margin of abdominal sternite VIII slightly sinuate. Aedeagus with wide basal portion, slightly narrowed toward middle, with long median lobe, from widest basal portion gradually narrowed toward middle and from middle slightly broadened apicad toward spear-shaped apical portion with rounded apex; mediolateral portions with moderately long sclerotized accessory plates (“accessory lamella” according Zanetti 1987) rounded apically; parameres moderately wide, significantly shorter than apex of median lobe, distinctly curved in preapical portions, with moderately wide rounded apices, each with three long apical setae; internal sac wide and long, with paired oval structures in basal portion ( Fig. 5 ). Lateral aspect of the aedeagus as in Fig. 6 ; apical portion of median lobe narrow, slightly broadened and curved apically ( Fig. 7 ).

Female. Antennomeres 9–10 slightly elongate. Posterior margin of abdominal tergite VIII straight. Posterior margin of abdominal sternite VIII rounded. Accessory sclerite with very wide basal portion and moderately long median part, strongly narrowing apicad toward acute apex ( Fig. 8 ). Spermatheca as in Fig. 9 .

Comparative notes. Omalium acutangulum sp. n. can be distinguished from O. amicorum sp. n. by the shape of posterior portion of the head, with temples slightly narrowed posteriad, the stronger sculpture of the head in middle and on infraorbital portions, by the shape of the nuchal constriction not impressed in medioapical part, the distinctly broader preapical part of the pronotum, and details of the morphology of the aedeagus (see the key above).

Distribution. Omalium acutangulum sp. n. is known from several locations in central Nepal ( Fig. 19 ).

Etymology. The specific epithet is the Latin acutangulus, - a, - um (sharp-angled). It alludes to the shape of posterior portions of temples with sharp subacute angles.

Bionomics. Specimens were collected at elevations from 2700 to 2900 m a.s.l. Specimens from Bagmati were sifted from leaf litter, moss and dead wood in a forest with Rhododendron and oak. Specimens from Ghoropani Pass were sifted from leaf litter in a ravin (south slope) with maples and rhododendrons and from rotten wood with fungi or in leaf litter, rotten wood, moss and fungi in forest with rhododendrons and oaks.

Figures

FIGURE 19. Distribution of Omalium in the Himalayan region: O. acutangulum sp. n. (circles), O. amplissimum sp. n. (star), O. beesoni (squares), O. cariosum (diamonds), O. flavotestaceum sp. n. (triangles).

FIGURES 1–4. Habitus (Figs 1, 3) and dorsolateral view of head and pronotum (Figs 2, 4) of Omalium: 1–2—O. acutangulum (paratype), 3–4—O. amicorum (paratype). Scale bars: 1.0 mm.

FIGURES 5–7. Aedeagus of Omalium acutangulum (holotype): 5—aedeagus, parameral view, 6—aedeagus, lateral view, 7—median lobe, lateral view). Scale bar: 0.1 mm.

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.