Omalium niponense Sharp, 1889

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 : 222-224

3.2.4.6. Omalium niponense Sharp, 1889

( Figs 32 , 35 , 38–40 )

Omalium niponense Sharp, 1889: 474 ; Nakane 1963: 82, Watanabe 1990: 92.

Omalium (Omalium) niponense : Bernhauer & Schubert 1910: 55.

Type material examined. Holotype ♂ ( Fig. 35 ): ‘Type’ <round label with red margin, printed>, ‘ Japan. [underlined by yellow] | G. Lewis. | 1910-320.’ <printed>, ‘Kurigahara. | 4.VIII.–6.VIII.[18]81.’ <printed>, ‘ Omalium | niponense | Type D.S.’ <handwritten in black>, ‘NHMUK015009855’ <printed label with barcode on the right side>, ‘ Omalium | niponense Sharp, 1889 | Shavrin A.V. det. 2025’ <printed> ( BMNH).

Material examineD. JAPAN: HONSHU: 1 ♂: ‘ Futamata Shimashimadani Shimshiu 21-July-1936 Coll. Y. Yano’, ‘ No. 2653 Collection Yoshio Yano’, ‘ O. niponense Shp. ’, ‘ M. Cameron. Bequest. B.M. 1955-147.’ (BMNH); RUSSIA: MARITIME PROVINCE: 2 ♂♂: Sikhote-Alin Nature Reserve, Kabaniy Klyuch , 45°07’N 135°52’E. 500 m a.s.l., window traps. 24– 27.04.2015. D.E. Shcherbakov leg. (cR, cSh).

Redescription. Measurements (n=4): HW: 0.60–0.70; HL: 0.40–0.45; OL: 0.15–0.16; TL: 0.07–0.10; AL (holotype): 1.17; PL: 0.47–0.52; PWmax: 0.73–0.82; PWmin: 0.68–0.70; ESL: 0.86–1.10; EW: 0.95–1.12; MTbL (holotype): 0.45; MTrL (holotype): 0.25 (MTrL 1–4: 0.10; MTrL 5: 0.15); AW: 0.97–1.13; AedL: 0.55–0.62; BL: 3.17 (holotype)–3.70.

Habitus as in Fig. 35 . Body yellowish-brown to reddish-brown, usually with slightly paler lateral and basal portions of pronotum, elytra and paratergites of abdomen; antennomeres 5–11 or 6–11 brown; mouthparts, antennomeres 1–4 or 1–5 and legs yellowish to yellow-brown (tarsi sometimes paler). Punctation of head variable, fine or moderately large, sparse or dense, usually denser in middle; neck with sparse fine punctation; punctation of pronotum about as that in middle portion of head, by slightly larger, usually finer and sparser in middle and mediobasal portion (specimens from Russia with significantly denser and more regular punctation); punctation of elytra denser, larger and deeper than that on pronotum; abdominal tergites with sparse and fine, sometimes indistinct, punctation. Anterior portion of clypeus with fine transverse microsculpture; scutellum without or with fine isodiametric meshes; abdominal tergites with dense isodiametric microsculpture. Anterior portion of clypeus with several erect long setae; posterior margin of pronotum and sometimes posterior margins of elytra with short cuticular fringe.

Head 1.5 times as broad as long, flattened or slightly elevated in middle, with widely broadened clypeus and strongly elevated, distinctly explanate supra-antennal elevations; anteriomedian depressions wide and deep, reaching level of anterior third of eyes; posteriolateral margins of clypeus somewhat parallel-sided or slightly narrowed basad, reaching level of anterior third of eyes. Mediodorsal surface with irregular diagonal elevations between punctures in middle and with longitudinal elevations on posterior parts of infraorbital portions, postocular portions sometimes forming three to four narrow, sometimes indistinct, elongate wrinkles. Anteocellar foveae suboval, deep and slightly elongate, convergent lateroapicad toward level of posterior third or middle of eyes. Temples 1.6 times to twice as long as longitudinal length of eye. Distance between ocelli 1.5–1.8 times as long as distance between ocellus and posterior margin of eye. Antenna with elongate antennomeres 6–8 and transverse 9–10; antennomeres 6–7 indistinctly broader than 5, 8 slightly shorter than 7, 9–10 slightly broader than 8, apical antennomere 1.3–1.5 times as long as preceding segment.

Pronotum convex, 1.5 times as broad as long, 1.1–1.2 times as broad as head, from widest middle more narrowed posteriad than anteriad. Surface of disc with two elongate, shallow or deep, longitudinal depressions; medioapical depression mising or present, small and shallow; surface between all pronotal depressions slightly or strongly elevated. Middle portion sometimes with irregular indistinct or distinct transverse and diagonal elevations between punctures.

Elytra slightly broader than long, 1.8 times to more than twice as long as pronotum, distinctly broadened posteriad.

Male. Posterior margin of abdominal tergite VIII straight or rounded. Posterior margin of abdominal sternite VIII slightly sinuate. Aedeagus with broadened basal portion, gradually narrowed toward middle; median lobe moderately wide, from widest middle gradually narrowed toward small rounded apex; mediolateral portions with short and relatively wide accessory plates, each rounded apically; parameres moderately narrow, significantly shorter than apex of median lobe, slightly curved and narrowed in preapical portion, each with one long and one short apical and two short preapical setae; internal sac narrow and long, with paired oval structures in basal portion ( Figs 38–39 ). Lateral aspect of the aedeagus as in Fig. 40 ; apical portion of median lobe narrow, with small rounded apex.

Female unstudied.

Comparative notes. Based on coloration and shape of the habitus and the aedeagus, O. niponense is similar to O. flavotestaceum Shavrin, 2023 , recently described from West Bengal, India (Shavrin 2023). It can be distinguished from it by the shape of the pronotum widest in middle, the shape of the shorter and broader median lobe, the narrower parameres, and other details of the morphology of the aedeagus.

Distribution. Omalium niponense is known from Maritime Province ( Russia) and Japan ( Fig. 32 ).

Bionomics. Detailed bionomical data from Japan are unknown, except for specimens collected in Ehime University Forest ( Ishihara et al. 1974), which were sifted under leaves. Specimens from Sikhote-Alin Nature Reserve were collected at an altitude of 500 m a.s.l. by window traps.

Remarks. Omalium niponense was originally described based on a single specimen from “Kashiwagi, 23rd June, 1881 …”. Watanabe (1990) redescribed it and provided additional material from Hokkaido, Honshu, Shikoku and Kyushu. Specimens from Maritime Province are slightly narrower than Japanese specimens. Besides that, they have denser punctation of the forebody, but the morphology of the aedeagus is without significant differences ( Figs 38, 40 ).

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

Figures

FIGURE 32. Distribution of Omalium in the eastern Palaearctic region: O. diffine (squares), O. kurilicum (stars), O. niponense (rounds). Black circles: material studied by author, white circles: previously published material not seen by author.

FIGURES 33–35. Habitus of Omalium: 33—O. japonicum (lectotype), 34—O. kurilicum (holotype), 35—O. niponense (holotype). Scale bar: 1.0 mm.

FIGURES 36–40. Aedeagus of Omalium (Figs 36–37—O. japonicum (Japan: Tsukuba Mt.), Figs 38–40—O. niponense (38— Japan: Futamata; 39–40—Russia: Maritime Province, Sikhote-Alin Nature Reserve)): 36, 38–39—aedeagus, parameral view, 37, 40—aedeagus, lateral view. Scale bar: 0.1 mm.