Diochus papuanus Cameron, 1939

Huang, Tian, Janák, Jiří & Zhou, Hong-Zhang, 2024, Taxonomy of the genus Diochus Erichson (Coleoptera: Staphylinidae, Staphylininae, Diochini) of Papua New Guinea, Vanuatu and Solomon Islands, Zootaxa 5519 (1), pp. 103-118 : 115-117

4. Diochus papuanus Cameron, 1939

( Fig 1C ; Fig 5 )

Cameron, 1939: 145 (Type locality: New Guinea: Kokoda, altitude 1200 feet).

Type material examined. PAPUA NEW GUINEA: Holotype: male, “ Type ” (printed rounded white, red boarded label) // “PAPUA: Kokoda. / 1,200ft. IX.1933. / L.E.Cheesman. / B.M.1933-427.” (printed) // “ Diochus / papuanus / TYPE Cam” (Cameronʼs handwriting, black and red inked) ( NHMUK).

Note. We examined the unique male type from the Cameronʼs collection ( NHMUK). The specimen was remounted, glued on a new card plate, aedeagus and last abdominal segments were embedded in Euparal on a plastic plate placed at the same pin as the specimens. As Cameron (1939) mentioned in the description “Unique” and the specimen was labeled as “Type” there is no doubt that it is a holotype of the species.

Measurements. BL = 4.0 mm, FL = 1.7 mm, HL = 0.51 mm, HW = 0.44 mm, EyL = 0.14 mm, TL = 0.30 mm, PL = 0.71 mm, PW = 0.59 mm, EL = 0.62 mm, EW = 0.68 mm, SL = 0.42 mm.

Redescription. Body ( Fig 1C ) long, narrowed anteriorly and posteriorly, medium-sized. Body entirely dark brown to black, posterior margins of abdominal segments and abdominal segments VIII−X lighter, dark reddish brown. Legs yellowish brown, tarsi distinctly lighter. Antennomeres 1−4 light brown, 5−11 yellowish, apex of each antennomere lighter. Maxillary and labial palpi yellowish brown.

Head ( Fig 5A ). Relativelly short and wide, 1.17 times as long as wide. Tempora roundly widened posteriad, posterior angles widely rounded. Dorsal surface shiny, bearing very fine transverse microstriae and mesh, also with coarse and very sparse punctures. Head with 5−7 irregular punctures scattered around each eye and numerous smaller punctures on deflexed portion of tempus and near posterior margin. Each side of cranium with characteristic punctures: one frontal puncture on frontal region, two anterolateral punctures near antennal insertion, three lateral punctures near dorsal margin of eye, with temporal puncture and occipital puncture near basal margin; disc surface bearing two additional paired punctures in middle area. Frontal furrows and anteocular furrows absent. Eye large-sized, slightly protruding laterad, longitudinal diameter about half the length of tempora (eye: tempora = 0.45). Epistoma not flattened, abruptly oblique, anterior margin rounded. Ventral surface with scattered punctures, interspaces between them about 4 puncture diameters. Gular sutures deep, confluent at basal 1/4, then extended to base.

Antennae ( Fig 5B ). Scape rod-shaped, slightly thickened apically, shorter than two subsequent antennomeres combined; antennomere 2 slightly elongate, antennomere 3 slightly longer than 2; antennomere 4 almost twice the width, antennomere 4 to 10 gradually shortened, antennomere 4 observably longer than 10; antennomere 11 distinctly longer than 10.

Mouthparts. Labrum oval-shaped, lateral margin rounded, widest at basal 1/2; width of anterior margin is about half the width at the widest point. Mandibles falciform, left one with three small teeth on inner margin, whereas right one with two.

Neck. Cylindrical, shiny, only bearing shallow microsculpture, shorter than 1/3 of head width. First half of dorsal surface depressed, with distinct groove. Ventral surface with gular sutures forming obvious triangular region, with deep transverse median furrow.

Prothorax ( Fig 5A ). Pronotum elongate (PL to PW ratio 1.21), distinctly longer and wider than head. Anterior region near anterior angles deflexed, lateral margins widened posteriad to basal 1/3 (widest at 1/3), then convergent backwards, anterior and posterior angles broadly rounded. Dorsal surface glossy, extensively with micropunctures, but without any microsculpture. Each side of longitudinal midline with one row of punctures composing of 3 large punctures and 2 additional punctures outside of puncture row, several punctures scatted near each margin (including anterior, lateral and posterior margins). Prosternum bearing observable transverse ridge between basisternum and furcasternum, angularly backwards.

Pterothorax ( Fig 5A ). Mesoscutellum triangular and small, surface shiny, bearing distinct microstriae, but without any punctures. Transverse ridge on mesoventrite wave shaped; paired oblique furrows short but deep; carina limiting mesocoxal cavity slightly arcuate. Discrimen region on metaventrite normally elevated.

Elytra ( Fig 5A ). Slightly transverse (EL to EW ratio 0.95), only a sixth longer and but markedly wider than pronotum. Humeri well developed, lateral margins divergent posteriorly, posterior margin of each elytron obliquely truncate. Dorsal surface shiny, flattened, without microsculpture, finely coriaceous; each elytron with row of 5 punctures along suture, row of 6 punctures in median, two isolated punctures between sutural and median row, also with 6−7 punctures on deflexed portion.

Legs. First four segments of protarsi heart-shaped, moderately dilated, and those of meso- and metatarsi slender. Last segment of protarsi almost equal to 2−4 together, that of meso-, meta- slightly longer than length of each 2−3.

Abdomen. Broadest at segment V. Tergites III–VII covered with very fine shallow transverse microstriae and mesh; each tergite with dense pubescence, also with row of darker and coarser setae at posterior margin of tergites III–VI. Tergites III–VII with basal impression near anterior margin, respectively, each one only possessing one basal transverse carina; all abdominal tergites with fine and moderately dense puncturation, distance between punctures larger than diameter of puncture. Posterior margin of tergite VII with distinct palisade fringe. All abdominal sternites shiny, with microstriae and punctures as those on tergites.

Male ( Fig 5A ). Head with small shiny, slightly elongate, markedly protruding elevation between eyes. Posterior margin of sternite VIII markedly roundly emarginated medially, both sides apicolaterally obliquely truncate, apical margin with very short setae ( Fig 5C ). Posterior margin of tergite VIII arcuate ( Fig 5D ). Tergite IX ( Fig 5F ) symmetrical, connected mediobasally, narrowed apically. Sternite IX ( Fig 5E ) almost symmetrical, widest near basal 1/3; basal margin straight, apical margin normally emarginated. Tergite X ( Fig 5F ) symmetrical, triangular. Aedeagus ( Fig 5G ) symmetrical, medium-sized, ca. 0.49 mm long, normally sclerotized with apical margin triangularly emarginate. Parameres symmetrical, thick and relatively short, about 1/3 length of median lobe. Internal structures sclerotized, two paired strips shaped sclerites located on both sides, parallel, lateral one slender, in brown color, the other broader, in brown color; 3 sclerites in middle: paired rectangular sclerites in brown color, basally with one Y-shaped sclerite in brown color; proximally with paired of brush like structures consisting of long fibers. Sperm pump coiled, thinned toward apex.

Female. Unknown.

Diagnosis. The species can be easily separated from other species by its short elytra, which are a sixth shorter than the thorax and by deeply roundly emarginated male sternite VIII.

Distribution. Papua New Guinea.

Figures

FIGURE 1. Habitus of four species from Papua New Guinea, Vanuatu and Solomon Islands in dorsal view:A. Diochus elongatus sp. nov.; B. D. chambrieri sp. nov.; C. D. papuanus Cameron, 1939, D. D. loebli sp. nov. (Scale bar: 0.5 mm).

FIGURE 5. Diochus papuanus Cameron, 1939:A. forebody, dorsal view; B. antenna; C. male sternite VIII; D. male tergite VIII; E. male sternite IX; F. male tergites IX–X; G. aedeagus, dorsal view; H. labels. (Scale bars: A = 0.5 mm, B–G = 0.1 mm).