On Orsunius V. Seven new species from Borneo and Vietnam (Coleoptera: Staphylinidae: Paederinae: Medonina)

Seven species of Orsunius Assing, 2011 are described and illustrated, six of them from Borneo and one from Vietnam: Orsunius weigeli spec. nov. (North Vietnam), O. floreni spec. nov. (Malaysia: Sabah), O. flavoniger spec. nov. (Malaysia: Sabah), O. incitatus spec. nov. (Malaysia: Sabah), O. curvicollis spec. nov. (Malaysia: Sabah), O. tricolor spec. nov. (Malaysia: Sabah), and O. arboris spec. nov. (Malaysia: Sabah). The genus now includes 31 named extant species distributed in the southern East Palaearctic, the Oriental, and the northern Australian regions.


Introduction
The medonine genus Orsunius Assing, 2011 previously included 24 named extant species distributed in the Oriental, southern East Palaearctic, and the Australian regions (Assing 2011(Assing , 2014(Assing , 2015(Assing , 2020). An updated key and a catalogue of the species known at that time were provided by Assing (2015). Not a single species was previously known from Borneo. Since the latest contribution (Assing 2020), additional material of Orsunius has been examined, the majority of specimens and species collected by canopy fogging in North Borneo (Malaysia: Sabah) and the remainder from Vietnam. A study of this material revealed that the specimens represented nine undescribed species. Seven of them are described in the present paper. It should be noted, however, that the generic assignment of three of them is tentative. Two species remain undescribed for want of males.

Material and methods
The material treated in this study is deposited in the following public institution and private collection: MNB Museum für Naturkunde, Berlin cAss author´s private collection The morphological studies were conducted using Stemi SV 11 (Zeiss) and Discovery V12 (Zeiss) microscopes, and a Jenalab compound microscope (Carl Zeiss Jena). The images were created using digital cameras (Axiocam ERc 5s, Nikon Coolpix 995), as well as Labscope and Picolay software. Body length was measured from the anterior margin of the mandibles in resting position to the apex of the abdomen, the length of the forebody from the mandibles (in resting position) to the posterior margin of the elytra, head length from the anterior margin of the frons to the posterior constriction of the head, head width across and including the eyes, elytral length at the suture from the apex of the scutellum to the posterior margin of the elytra, and the length of the aedeagus from the apex of the ventral process to the base of the aedeagal capsule. The "parameral" side (i.e., the side where the sperm duct enters) is referred to as the ventral, the opposite side as the dorsal aspect.  Fig. 1. Colouration: head blackish; pronotum reddish; elytra yellowish to reddish, with the posterior portion yellow and with a more or less distinct and more or less extensive infuscate band extending from the middle of lateral margins obliquely postero-mediad; abdomen blackish with the posterior margins of segments VII and VIII reddish; legs yellow; antennae reddish-yellow. Head (Fig. 2) transverse, approximately 1.15 times as broad as long; lateral margins behind eyes parallel in dorsal view; posterior angles moderately marked; punctation very dense and umbilicate; interstices mostly forming narrow ridges, without microsculpture. Eyes rather large, as long as, or slightly longer than postocular portion in dorsal view. Antennae 1.2 mm long. Anterior margin of labrum deeply incised in the middle. Pronotum (Fig. 2) 1.05-1.10 times as broad as long and slightly broader than head; punctation similar to that of head; midline with narrow impunctate band of variable length posteriorly; interstices without microsculpture. Elytra (Fig. 2) slightly longer than pronotum; punctation fine and dense; interstices without microsculpture. Hind wings fully developed. Protarsomeres I-IV distinctly dilated, without sexual dimorphism. Metatarsomere I as long as the combined length of metatarsomeres II and III, or nearly so. Abdomen finely and densely punctate and pubescent; interstices with microsculpture; posterior margin of tergite VII with palisade fringe; posterior margin of tergite VIII weakly concave in the middle. : sternite VIII (Fig. 8) approximately as long as broad, with rather deep and broad V-shaped posterior excision; aedeagus (Figs 15-17) 0.75 mm long; ventral process distinctly separated from median lobe, asymmetric, near base with pronounced spine-shaped process.

Descriptions of new species
Comparative notes: Based on the similar external appearance (colouration; punctation; proportions) and particularly the similar male primary and secondary sexual characters, O. weigeli is undoubtedly very closely related to O. excisus Assing, 2011 (Taiwan, Thailand), from which the new species is distinguished by darker colouration (O. excisus: pronotum pale-reddish; elytral spot less distinct and less distinctive, or completely absent; abdominal segments VII-VIII extensively or completely yellow) and by the structure of the slightly larger aedeagus (O. excisus: aedeagus approximately 0.70 mm long; ventral process apically more strongly produced dorsad and with spine-shaped process in median position). For illustrations of the male sexual characters of O. excisus see Assing (2011). Etymology: This species is dedicated to Andreas Floren (University of Würzburg), who collected the material of this and the following species in a canopy fogging project in Sabah (Borneo).
Description: Body length 3.5 mm; length of forebody 2.0 mm. Habitus as in Fig. 3. Colouration: head and pronotum dark-brown; elytra reddish with the mediosutural portion diffusely darker; abdomen reddish-brown; legs yellowish red; antennae reddish. Head (Fig. 4) weakly transverse, 1.05 times as broad as long; lateral margins behind eyes parallel in dorsal view; posterior angles moderately marked; punctation very dense and umbilicate; interstices mostly forming narrow ridges, without microsculpture. Eyes rather large, nearly as long as postocular portion in dorsal view. Antennae short and stout, 0.9 mm long; preapical antennomeres strongly transverse. Anterior margin of labrum deeply and narrowly incised in the middle. Pronotum (Fig. 4) 1.1 times as broad as long and indistinctly broader than head; punctation similar to that of head; midline without impunctate band. Elytra (Fig. 4) approximately as long as pronotum; punctation dense, but less so than that of head and pronotum, and less coarse than that of head and pronotum; interstices without microsculpture. Hind wings fully developed. Protarsomeres I-IV undilated. Metatarsomere I shorter than the combined length of metatarsomeres II and III. Abdomen finely and densely punctate; interstices without microsculpture; posterior margin of tergite VII with palisade fringe; posterior margin of tergite VIII convex. : sternite VIII (Fig. 21) weakly oblong, with broadly and weakly concave posterior margin; aedeagus 0.62 mm long and shaped as in Figs 19-20.
Comparative notes: Orsunius floreni is distinguished from all its congeners by the distinctive structure of the aedeagus. It is additionally characterised by a male sternite VIII with a broadly concave posterior margin, by conspicuously coarse, dense, and umbilicate punctation of the head and pronotum, and by short and stout antennae. For illustrations of other species of the genus see Assing (2011Assing ( , 2014Assing ( , 2015Assing ( , 2020.

Distribution and natural history:
The type locality is situated in Tawau Hills (Malaysia: Sabah), North Borneo. The holotype was collected from Microcos antidesmifolia by canopy fogging.

Etymology:
The specific epithet (Latin, adjective: aroused) alludes to the shape of the ventral process of the aedeagus (lateral view).
Description: Body length 3.6-3.7 mm; length of forebody 2.0 mm. Habitus as in Fig. 5. Colouration: head black; pronotum blackish-brown to black; elytra reddish to blackish-brown with the humeral angles and the posterior margins diffusely paler; abdomen blackishbrown with the posterior margins of the tergites diffusely and narrowly paler; legs reddish-yellow; antennae reddish. Head (Fig. 11) weakly transverse, 1.06-1.08 times as broad as long; lateral margins behind eyes parallel in dorsal view; posterior angles moderately marked; punctation rather sparse and fine; interstices without microsculpture. Eyes large, approximately as long as postocular portion in dorsal view, or nearly so. Antennae 1.1-1.2 mm long. Anterior margin of labrum deeply incised in the middle. Mandibles each with three rather short teeth. Pronotum (Fig. 11) approximately 1.15 times as broad as long and as broad as head; lateral margins weakly sinuate; punctation similar to that of head; midline with somewhat irregular and rather broad impunctate band; interstices without microsculpture. Elytra (Fig. 11) slightly longer than pronotum; punctation much denser and finer than that of head and pronotum; interstices without microsculpture. Hind wings fully developed. Protarsomeres I-IV weakly dilated, without sexual dimorphism. Metatarsomere I shorter than the combined length of metatarsomeres II and III. Abdomen finely and densely punctate and pubescent; interstices without microsculpture, glossy; posterior margin of tergite VII with palisade fringe; posterior margin of tergite VIII weakly convex.

Etymology:
The specific epithet is an adjective composed of the Latin adjectives flavus (yellow) and niger (black). It alludes to the distinctly bicoloured elytra.
Description: Body length 4.3-5.5 mm; length of forebody 2.5-2.7 mm. Habitus as in Fig. 6. Colouration: forebody blackish with the posterior margins of the elytra sharply yellow; abdomen yellow with the posterior margins of tergites VII and VIII rather broadly and sharply yellow; legs reddish with darker femora; antennae red. Head (Fig. 7) transverse, 1.10-1.15 times as broad as long; lateral margins behind eyes parallel in dorsal view; posterior angles marked; punctation dense and rather coarse; interstices without microsculpture. Eyes moderately large, approximately 0.6-0.7 times as long as postocular portion in dorsal view. Antennae approximately 1.2 mm long. Anterior margin of labrum deeply and narrowly incised in the middle. Mandibles each with two stout teeth. Pronotum (Fig. 7) approximately 1.15 times as broad as long and slightly narrower than head; lateral margins weakly sinuate; punctation similar to that of head; midline with more or less distinct, narrow impunctate band; interstices without microsculpture. Elytra (Fig. 7) approximately as long as pronotum; punctation finer than that of head and pronotum; interstices without microsculpture. Hind wings fully developed. Protarsomeres I-IV slender, not dilated. Metatarsomere I as long as the combined length of metatarsomeres II and III, or nearly so. Abdomen finely and densely punctate and pubescent; interstices with very shallow microsculpture, glossy; posterior margin of tergite VII with palisade fringe; posterior margin of tergite VIII weakly convex. : sternite VIII (Fig. 27) weakly transverse, posterior margin of distinctive shape, distinctly bisinuate; aedeagus (Figs 25-26) 0.57-0.63 mm long; ventral process very slender in lateral view, basally broad and apically acute in ventral view.

Comparative notes:
Orsunius flavoniger is distinguished from all other representatives of the genus by the morphology of the aedeagus and by the shape of the male sternite VIII, from the vast majority of species additionally by the colouration. The only other congener with a similarly coloured forebody is O. tortus Assing, 2020 from Thailand, from which O. flavoniger also differs by smaller and less convex eyes and much coarser and less dense punctation of the forebody. For illustrations of O. tortus see Assing (2020).

Distribution and natural history:
The species is currently known from two localities in Kinabalu Park (Malaysia: Sabah), Borneo. The specimens were collected from Vitex pinnata and an unidentified species of Meliaceae by canopy fogging. The female paratype is teneral.

Etymology:
The specific epithet is an adjective composed of the Latin adjective curvus (bent, curved) and the adjectival suffix -collis (of the neck). It alludes to the distinctly sinuate lateral margins of the pronotum. Description: Small species; body length 2.5-2.6 mm; length of forebody 1.25-1.35 mm. Habitus as in Fig. 8. Colouration: forebody dark-brown to black with the posterior margin of the elytra broadly bright yellow; abdomen dark-brown to black; legs yellow with the femora infuscate; antennae yellow. Head (Fig. 12) distinctly transverse, 1.18 times as broad as long, and somewhat wedge-shaped; lateral margins behind eyes slightly diverging in dorsal view; posterior angles marked; punctation moderately dense and very fine; interstices without microsculpture. Eyes large, slightly longer than postocular portion in dorsal view. Antennae 0.6-0.7 mm long. Anterior margin of labrum broadly excavate, this excavation acute in the middle. Mandibles each with two short teeth. Pronotum (Fig. 12) approximately 1.2 times as broad as long and slightly broader than head; lateral margins strongly sinuate; punctation as dense as that of head, but even finer; midline without impunctate band; interstices without microsculpture. Elytra (Fig. 12) approximately 1.2 times as long as pronotum; punctation less fine than that of pronotum; interstices without microsculpture. Hind wings fully developed. Protarsomeres I-IV unmodified (not dilated), without sexual dimorphism. All tarsi very short; metatarsomere I shorter than the combined length of metatarsomeres II and III. Abdomen finely and densely punctate; interstices without microsculpture, glossy; posterior margin of tergite VII with palisade fringe; posterior margin of tergite VIII weakly convex. : sternite VIII (Fig. 30) weakly transverse, with weakly convex posterior margin; aedeagus (Figs 28-29) minute, 0.25 mm long; ventral process short and weakly sclerotized; internal sac with two long sclerotised apical structures.
Comparative notes: This species is assigned to Orsunius with some hesitation, since it differs from other species of the genus not only by the structure of the aedeagus and the shape of the male sternite VIII, but also by the shape of the labrum, the structure of the mandibles, and the shape of the head. It is distinguished from other congeners of similarly small size by the colouration and the strongly sinuate lateral margins of the pronotum alone. For illustrations of previously described Orsunius species see Assing (2011Assing ( , 2014Assing ( , 2015Assing ( , 2020.

Distribution and natural history:
The type locality is situated near Poring Hot Springs (Malaysia: Sabah), North Borneo. The specimens were collected from Aporosa sp. by canopy fogging.

Etymology:
The specific epithet (Latin) alludes to the distinctly tricoloured forebody. Description: Small species; body length 2.9-3.2 mm; length of forebody 1.7 mm. Habitus as in Fig. 9. Colouration: head black; pronotum bright reddish; elytra black with the humeral angles and the broad posterior margins yellowish-red; abdomen black with the apex (segments VIII-X and posterior portion of VII) reddish-yellow; legs yellowish-red with the femora darker; antennae reddish. Head (Fig. 13) indistinctly transverse, approximately 1.05 times as broad as long; lateral margins behind eyes parallel in dorsal view; posterior angles moderately marked; punctation moderately dense and very fine; interstices without microsculpture. Eyes moderately large and weakly convex, slightly more than half as long as postocular portion in dorsal view. Antennae 0.8-0.9 mm long. Anterior margin of labrum with small, narrow, and moderately deep median excision. Pronotum (Fig. 13) weakly oblong, approximately 1.05 times as long as broad and 0.9 times as broad as head; lateral margins straight; punctation similar to that of head; midline with weakly defined impunctate band; interstices without microsculpture. Elytra (Fig. 13) approximately as long as pronotum; punctation fine and moderately dense; interstices without microsculpture. Hind wings fully developed. Protarsomeres I-IV weakly dilated. Metatarsomere I shorter than the combined length of metatarsomeres II and III. Abdomen finely and densely punctate; interstices with very shallow microsculpture visible only at high magnification (100 x); posterior margin of tergite VII with palisade fringe; posterior margin of tergite VIII truncate.
Comparative notes: As in the preceding species, the generic assignment of O. tricolor should be considered tentative. This species is distinguished from all other known representatives of the genus by the conspicuous colouration and an oblong pronotum alone. It is additionally characterised by the structure of the aedeagus and the shape of the male sternite VIII.
Distribution and natural history: The material was found in two close localities in Mesilau (Malaysia: Sabah), North Borneo. The specimens were collected from Vaccinium sp. and Phyllocladus hypophyllus by canopy fogging.
Orsunius arboris spec. nov. urn:lsid:zoobank.org:act:F3A3DD0D-3B71-4FE3-9D76-A8C5139E7AB2 (Figs 10,14,(34)(35)(36)(37) Fig. 10. Colouration: body pale-reddish to dark-reddish except for a broad transverse blackish band extending across posterior three-fifths of elytra, this band not reaching posterior margins of elytra; legs yellow to yellowish-red; antennae reddish. Head (Fig. 14) of rather variable shape, usually 1.10-1.15 times as broad as long; lateral margins behind eyes parallel or weakly converging in dorsal view; posterior angles moderately marked; punctation dense and moderately coarse; interstices without microsculpture. Eyes moderately large and distinctly convex, approximately as long as postocular portion in dorsal view. Antennae 0.7-0.8 mm long. Anterior margin of labrum with small V-or U-shaped median excision. Mandibles with two or three teeth. Pronotum (Fig. 14) approximately as broad as long, broadest at anterior angles, and slightly narrower than head; lateral margins straight; punctation extremely dense, granulosely umbilicate, and largely confluent, rendering the disc nearly matt; midline with very narrow, often incomplete impunctate band. Elytra (Fig. 14) approximately 1.2 times as long as pronotum; punctation fine and rather dense; interstices without microsculpture. Hind wings fully developed. Protarsomeres I-IV not distinctly dilated, without sexual dimorphism. Metatarsomere I shorter than the combined length of metatarsomeres II and III. Abdomen finely and densely punctate; interstices without microsculpture except near anterior margins of tergites; posterior margin of tergite VII with palisade fringe; posterior margin of tergite VIII weakly convex. : sternite VIII (Fig. 37) approximately as long as broad, with convex posterior margin; aedeagus (Figs 34-36) minute and weakly sclerotised, 0.23-0.25 mm long (without apical internal structures); ventral process weakly sclerotised and short; internal sac with a pair of long and moderately sclerotised apical structures and with a basal pair of dark series of small spines.
Comparative notes: Among the known Orsunius species, this species is characterised by the conspicuous colouration, the punctation of the pronotum, and by the structure of the aedeagus. In view of the morphology of the aedeagus, which considerably differs from that of previsouly described Orsunius species, the generic assignment should be considered preliminary.