Euconnus (Euconnus) oscillans Sharp, 1886

Jałoszyński, Paweł, 2022, Euconnus Thomson of Japan: redescriptions of species established by Reitter, Sharp and Franz, new synonyms, and summary of current state of knowledge (Coleoptera, Staphylinidae, Scydmaeninae), Zootaxa 5093 (1), pp. 1-37 : 18-20

Euconnus (Euconnus) oscillans Sharp

Euconnus oscillans Sharp, 1886: 48 .

( Figs 64–69 )

Type material studied. Holotype: ♂ ( Fig. 64 ), mounted on thick card with annotation: “ Euconnus osci- / lans. Type / D.S. / Hitoyoshi. / 3.5.81. Lewis.”, with two labels ( Fig. 65 ): “ Japan / G. Lewis. / 1910-320” [white with orange horizontal line, printed], and circular label “Type / H.T.” [white with red margin, printed] ( NHM).

Additional material studied. HONSHU: Nara Pref.: ♀, near Mt. Kasuga-yama , Nara City , 05.05.2001, T. Tsuru leg. (cPJ) .

Emended diagnosis. Among Japanese species, E. oscillans can be identified by: small body (BL ~ 1.2 mm); conspicuous setal pattern: head covered with very thin and short, moderately dense suberect setae, lacking thick bristles, pronotum densely covered with setae and bristles, and elytra moderately densely covered with suberect setae much longer and thicker than those on head; relatively compact antennae with antennomeres 3–7 each about as long as broad and distinct tetramerous club; head covered densely with fine punctures, pronotum with inconspicuously fine punctures, but elytra densely, deeply, distinctly punctate; pronotum with one pair of shallow lateral antebasal pits, connected by superficial transverse impression covered densely with fine punctures, and with a pair of short but distinct sublateral carinae, broadest indistinctly behind middle; legs in male unmodified; and aedeagus stout, with presumably subtriangular apex of mediodistal region of dorsal plate and a complex set of strongly asymmetrically distributed endophallic sclerites.

Redescription. Body of male ( Fig. 64 : holotype) moderately slender, strongly convex, BL 1.14 mm; cuticle glossy, pigmentation light brown with slightly reddish hue, vestiture of setae and bristles slightly lighter than cuticle.

Head elliptical, slightly elongate and broadest at eyes, HL 0.23 mm, HW 0.25 mm; tempora in dorsal view about twice as long as eyes and weakly converging posterad, weakly but distinctly rounded; vertex and frons confluent, weakly and evenly convex, posterior margin of vertex rounded, posteriorly convex, not bulging posterodorsad; supraantennal tubercles feebly marked; frons between antennae steeply declining; clypeus unmodified. Eyes moderately large and finely faceted, weakly projecting laterad from the head silhouette, in lateral view oval. Head densely covered with fine and superficial punctures, so that surface of vertex and frons appears semi-glossy; setae moderately dense and long, suberect, directed posterad, thick bristles lacking. Antennae slender and moderately compactly assembled, with distinct tetramerous clubs, AnL 0.53 mm; antennomeres 1–2 distinctly elongate, 3–7 each about as long as brad, 8–10 each distinctly transverse, 11 slightly elongate, as broad as 10.

Pronotum bell-shaped with rounded sides, widest slightly behind middle, but dense vestiture in intact specimens may obscure the shape, PL 0.26 mm, PW 0.28 mm; anterior margin nearly straight and much shorter than posterior margin, anterior corners indistinct, sides of pronotum strongly rounded and strongly converging anterad; posterior corners strongly obtuse-angled, well-marked; posterior margin weakly arcuate. Pronotal base with shallow transverse impression covered densely with fine and shallow punctures, one pair of lateral antebasal pits is situated within this impression, sublateral carinae sharply marked. Disc covered with inconspicuously fine punctures, densely covered with thin, suberect setae and thick, straight bristles distributed not only on sides, but also on dorsum (in holotype male partly broken off).

Elytra oval, broadest distinctly in front of middle, EL 0.65 mm, EW 0.50 mm, EI 1.30; basal impressions shallow but distinct, humeral calli prominent and weakly elongate, each delimited from adscutellar region by round impression; elytral apices separately rounded. Punctures on elytral disc conspicuously large and dense, those on anterior half separated by spaces subequal to their diameters, punctures reducing in diameter and depth toward sides and apices; setae moderately dense and long, but clearly longer than those on head, suberect. Hind wings long, functional.

Legs moderately long and slender, unmodified.

Abdomen unmodified.

Aedeagus ( Figs 66–69 ) in the only known male slightly damaged, with apex of median lobe broken off and proximal half of median lobe distorted; stout, AeL 0.19 mm; median lobe in ventral view broadest in subapical region, ventral apical plate subtriangular with rounded apex, dorsal apical plate longer, presumably with subtriangular median projection; endophallic structures asymmetrical, with several elongate and curved sclerites of various shapes and lengths distributed in sub-median and subapical regions. Parameres slender and long, but not reaching apex of median lobe, in lateral view parameres weakly curved in proximal half, each with 3–4 long subapical setae.

Female. Externally indistinguishable from male. BL 1.20 mm; HL 0.23 mm, HW 0.25 mm, AnL 0.53 mm; PL 0.28 mm, PW 0.30 mm; EL 0.70 mm, EW 0.53 mm, EI 1.33.

Distribution. Japan: Honshu, Kyushu.

Remarks. The aedeagus of the only known male of E. oscillans has been partly damaged during a previous, unskillful preparation, and the true shape of the dorsal mediodistal plate remains unknown. It closely resembles the aedeagus illustrated by Hoshina (2020) for E. akane , based on a male collected on Shikoku. However, the shapes and arrangement of the endophallic sclerites in E. akane , if illustrated correctly, seem different (although also as strikingly asymmetrical as those in E. oscillans ). According to Hoshina (2020), adults of E. akane measure 1.42‒1.43 mm of body length and have inconspicuous punctures on the elytra. In contrast, the male and female of E. oscillans examined during the present study measure 1.14‒1.20 mm, and have strikingly dense, deep and distinct elytral punctures. Therefore, it seems that these are two distinct species. The conspicuous elytral punctation of E. oscillans is unique among Japanese species.

Euconnus oscillans is here placed in Euconnus (s. str.), based on a tetramerous antennal club, pronotum bellshaped, broadest behind middle, lack of the median antebasal pronotal pit and a non-emarginate aedeagal apex.

The holotype male of Euconnus oscillans comes from Hitoyoshi, Kumamoto Prefecture, southern Kyushu, and collecting circumstances remain unknown. The only additional specimen available to my study was found in Nara City, (Nara Prefecture, SC Honshu), nearly 550 km NE of the terra typica. Unfortunately, no additional collecting data are available, except for near Mt. Kasuga, Tullgren. This suggests sifted leaf litter, as Mt. Kasuga east of Nara is covered with and surrounded by the Mt. Kasuga Primeval Forest .

Figures

FIGURES 64–69. Euconnus oscillans, male. Dorsal habitus (64) and annotated mounting card with historical labels (65) of holotype; aedeagus in ventral (66, 68) and lateral (67, 69) views.