Omalium, Gravenhorst, 1802, Gravenhorst, 1802

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 : 153-154

3.2.1. Acutangulum group

Diagnosis. Temples slightly or strongly narrowed posteriad, with subacute angles distinctly protruded basad. Apical half of nuchal constriction impressed, without ( Fig. 2 ) or with moderately wide and deep medioapical depression ( Fig. 4 ). Aedeagus with very wide basal portion and elongate moderately narrow median lobe; parameres short, not reaching apex of median lobe, moderately broad in middle, slightly or strongly narrowed apically.

Species included: O. acutangulum sp. n., O. amicorum sp. n.

Remarks. Species of the Acutangulum group differs from other species of the genus by the unusual shape of the posterior portions of the head with distinctly subacute temporal angles ( Figs 2, 4 ) and the presence of an modified apical half of the nuchal constriction, with the presence of distinct depression, significantly larger and deeper in O. amicorum sp. n. ( Fig. 4 ). Based on the general shape of the aedeagus, with the spear-shaped moderately narrow median lobe, species of the Acutangulum group are somewhat similar to some species of the Rivulare group (see below).

3.2.1.1. Key to Acutangulum group

1 Temples slightly narrowed posteriad. Infraorbital portions of head with strong longitudinal elevations. Medioapical part of nuchal constriction without distinct depression ( Fig. 2 ). Apical part of pronotum distinctly transverse, broader than basal part. Preapical parts of median lobe and parameres moderately broad ( Fig. 5 ); inner margin of preapical part of median lobe without tooth, if see laterally as in Fig. 7 . Female accessory sclerite as in Fig. 8 . Habitus as in Fig. 1 . Body length: 2.45–3.40 mm. Nepal.............................................................................. O. acutangulum sp. n.

- Temples strongly narrowed posteriad. Infraorbital portions of head without or with relatively fine elevations. Medioapical part of nuchal constriction significantly depressed ( Fig. 4 ). Apical part of pronotum moderately narrow, about as broad as basal part. Preapical parts of median lobe and parameres narrow ( Fig. 20 ); inner margin of preapical part of median lobe forming two large obtuse teeth, if see laterally as in Fig. 22 . Female accessory sclerite as in Fig. 10 . Habitus as in Fig. 3 . Body length: 3.15–3.50 mm. Nepal............................................................................ O. amicorum sp. n.

Figures

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.

FIGURES 20–22. Aedeagus of Omalium amicorum (holotype): 20—aedeagus, parameral view, 21—aedeagus, lateral view, 22—median lobe, lateral view). Scale bar: 0.1 mm.