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 : 186-187

3.2.5. Rivulare group

Diagnosis. Median lobe narrow, in middle part significantly narrower than basal portion; parameres complicated, broadened apically, usually with long apical setae.

Species included: O. angustissimum sp. n., O. cariosum Cameron, 1924 , O. flavotestaceum sp. n., O. kumari sp. n., O. latocavum sp. n., O. nigrum Coiffait, 1982 , O. secretum Cameron, 1924 .

Remarks. The Rivulare group was originally erected for eight Western Palaearctic species by Zanetti (1987). Later, the same author(Zanetti 2022)added to this group several additional species from Cyprus, Turkey and Caucasus. The Himalayan species have deeper and broader anteocellar foveae usually distinctly divergent lateroapicad about as that in species of the Oxyacanthae group (see above). Based on the general shape of the aedeagus, species of the Rivulare group differs from other groups by the distinctly narrower median lobe. Two species, originally described from Japan, O. japonicum Sharp, 1874 (this species is also known from Korea and north-western China ( Schülke & Smetana 2015)) and O. niponense Sharp, 1889 belongs to this group (see figures of the aedeagi in Watanabe 1990).

3.2.5.1. Key to Rivulare group of the Himalayan region

1 Temples short, about twice as long or shorter than longitudinal length of eyes, gradually narrowed toward nuchal constriction ................................................................................................... 2

- Temples moderately long, distinctly less than twice as long as longitudinal length of eyes, with convex and widely rounded temples............................................................................................. 3

2 Temples very short, distinctly more than twice shorter than longitudinal length of eyes. Pronotum widest in middle. Elytra about as long as broad. Median lobe moderately short and narrow; parameres short and very wide ( Fig. 73 ); apical part of median lobe forming subacute tooth if see laterally as in Fig. 75 . Female accessory sclerite as in Fig. 76 . Body reddish-brown, with yellow-brown elytra. Habitus as in Fig. 70 . Body length: 2.85–3.15 mm. India..................... O. cariosum Cameron, 1924

- Temples slightly longer, about twice shorter than longitudinal length of eyes. Pronotum widest in apical third. Elytra slightly broader than long. Median lobe elongate and moderately wide; parameres longer, distinctly narrowed in preapical portion ( Fig. 84 ); apical part of median lobe without tooth if see laterally as in Fig. 86 . Female accessory sclerite as in Fig. 77 . Body yellow-brown, with darker head. Habitus as in Fig. 71 . Body length: 2.49–3.55 mm. India, Nepal.......... O. flavotestaceum sp. n.

3 Pronotum widest in apical third. Median lobe with distinctly widened portion in middle, from middle strongly narrowed apicad and from preapical part slightly broadened toward apex ( Fig. 87 ). Female accessory sclerite as in Fig. 79 . Body reddish-brown. Habitus as in Fig. 72 . Body smaller: 2.40–3.00 mm. Nepal......................................... O. kumari sp. n.

- Pronotum widest in or slightly above middle. Median lobe different............................................. 4

4 Pronotum gradually narrowed both apicad and posteriad...................................................... 5

- Pronotum more narrowed posteriad than apicad............................................................. 6

5 Elytra slightly less than twice as long as pronotum. Punctation of pronotum and elytra very dense and coarse. Median lobe spear-shaped, slightly broadened in preapical portion; apical portions of parameres very wide ( Fig. 93 ); preapical portion of median lobe with distinct obtuse hook, if see laterally as in Fig. 95 . Female accessory sclerite as in Fig. 81 . Body reddish-brown. Habitus as in Fig. 90 . Body larger: 3.06–3.28 mm. Nepa................................. O. latocavum sp. n.

- Elytra about twice as long as pronotum. Punctation of pronotum and elytra sparse and fine. Median lobe narrow, from widest median part gradually narrowed apically; preapical portions of parameres narrow ( Fig. 100 ); preapical portion of median lobe without hook, if see laterally as in Fig. 102 . Female accessory sclerite as in Fig. 82 . Body yellow-brown to reddish-brown. Habitus as in Fig. 92 . Body length: 2.35–3.28 mm. India, Nepal........................................ O. secretum

6 Apical angles of pronotum not protruded anteriad. Parameres wide ( Fig. 66 ). Body dark-brown. Habitus as in Fig. 58 . Body length: 2.76 mm. Nepal.............................................................. O. angustissimum sp. n.

- Apical angles of pronotum slightly protruded anteriad. Parameres moderately narrow ( Fig. 96 ). Body brown to dark-brown. Habitus as in Fig. 91 . Body length: 2.80–3.00 mm. Nepal.............................................. O. nigrum

Figures

FIGURES 73–75. Aedeagus of Omalium cariosum (paralectotype): 73—aedeagus, parameral view, 74—aedeagus, lateral view, 75—median lobe, lateral view. Scale bar: 0.1 mm.

FIGURES 76–83. Female accessory sclerite (Figs 76–77, 79, 81–82) and spermatheca (Figs 78, 80, 83) of Omalium: 76— O.cariosum, 77–78—O. flavotestaceum, 79–80—O. kumari, 81—O. latocavum, 82–83—O. secretum. Scale bar: 0.1 mm.

FIGURES 70–72. Habitus of Omalium: 70—O. cariosum (lectotype), 71—O. flavotestaceum (paratype), 72—O. kumari (paratype). Scale bars: 1.0 mm.

FIGURES 84–86. Aedeagus of Omalium flavotestaceum (paratype): 84—aedeagus, parameral view, 85—aedeagus, lateral view, 86—median lobe, lateral view. Scale bar: 0.1 mm.

FIGURES 87–89. Aedeagus of Omalium kumari (holotype): 87—aedeagus, parameral view, 88—aedeagus, lateral view, 89— median lobe, lateral view. Scale bar: 0.1 mm.

FIGURES 93–95. Aedeagus of Omalium latocavum (holotype): 93—aedeagus, parameral view, 94—aedeagus, lateral view, 95—median lobe, lateral view. Scale bar: 0.1 mm.

FIGURES 90–92. Habitus of Omalium: 90—O. latocavum (paratype), 91—O. nigrum (holotype), 92—O. secretum (Nepal: Parbat). Scale bars: 1.0 mm.

FIGURES 100–102. Aedeagus of Omalium secretum (Nepal, Parbat): 100—aedeagus, parameral view, 101—aedeagus, lateral view, 102—median lobe, lateral view. Scale bar: 0.1 mm.

FIGURES 66–68. Aedeagus of Omalium angustissimum (holotype): 66—aedeagus, parameral view, 67—aedeagus, lateral view, 68—median lobe, lateral view. Scale bar: 0.1 mm.

FIGURES 56–58. Habitus of Omalium: 56—O. marginatum (holotype), 57—O. scapulare (Nepal, Bagmati), 58—O. angustissimum (holotype). Scale bars: 1.0 mm.

FIGURES 96–98. Aedeagus of Omalium nigrum (Nepal: Mahakali): 96—aedeagus, parameral view, 97—aedeagus, lateral view, 98—median lobe, lateral view. Scale bar: 0.1 mm.