Euconnus (Napochus) bachmamontanus, 2018

Jałoszyński, Paweł & Nomura, Shûhei, 2018, A new Vietnamese species of Euconnus (Napochus) with modified antennal club (Coleoptera: Staphylinidae: Scydmaeninae), Zootaxa 4521 (1), pp. 133-136 : 134

Euconnus (Napochus) bachmamontanus sp. n. ( Figs 1–7 )

Material studied. Holotype: VIETNAM: ♂, two labels: "FIT: Mt.Bach Ma (1,150m) / T.T. Hue Prov. / [C-VIETNAM] / 5-10.v.2003, S. Nomura leg." [white, printed], " EUCONNUS / ( NAPOCHUS ) / bachmamontanus m. / Jałoszyński & Nomura, '18 / HOLOTYPUS " [red, printed] (NSMT). Paratype: 1 ♂, same data as for holotype ( NSMT) .

Diagnosis. Napochus with pronotum broadest at base, and with a sharply delimited, tetramerous club, which is modified in males: antennomeres VIII and X symmetrical and transverse, IX elongate, slightly broader than VIII and X– XI, asymmetrical, with a deep dorsal cavity occupying its proximal half; aedeagus with a subtriangular and rounded ventral plate flanked by a pair of elongate projections with apices twisted laterad, dorsal plate similar in shape to ventral plate but with more broadly rounded apex.

Description. Body of male ( Fig. 1 ) moderately stout and strongly convex, darkish brown, covered with yellowish vestiture. BL 1.63–1.68 mm.

Head in dorsal view short and transverse, moderately convex, broadest at eyes, HL 0.30–0.33 mm, HW 0.38 mm; vertex convex, frons between eyes convex, in front of eyes flattened, rapidly declines anterad; tempora in lateral view much shorter than eyes, in dorsal view strongly and evenly curved mesad; eyes large, coarsely faceted and strongly convex, bean-shaped; frons and vertex with fine and inconspicuous punctures and sparse, long and suberect setae posteriorly and lateroposteriorly replaced by relatively thin but long bristles. Antennae ( Figs 1–3 ) moderately long and slender, AnL 0.83–1.00 mm, antennal club ( Figs 2–3 ) tetramerous, sharply delimited and as long as half AnL, antennomeres I and II elongate, III–VII each about as long as broad, VIII symmetrical and about as long as broad, IX asymmetrical, elongate, broader than remaining club segments, with large and deep dorsal cavity occupying its proximal half, X symmetrical, distinctly transverse, XI slightly asymmetrical, indistinctly elongate. Antennae covered with sparse, long and erect setae

Pronotum subtrapezoidal, broadest at base; PL 0.40–0.43 mm, PW 0.45–0.48 mm. Anterior and posterior margins weakly angulate, sides rounded and strongly convergent anterad, in anterior 1/5 rapidly but only slightly more narrowed. Pronotal base with a lateral pair of small but distinct pits connected by a distinct transverse impression, sublateral carinae indistinct. Punctures superficial, inconspicuous; setae long, sparse, suberect to erect, bristles on sides relatively thin.

Elytra more convex than pronotum, oval, broadest distinctly in front of middle; EL 0.93 mm, EW 0.80 mm, EI 1.16. Elytral base with distinct and strongly elongate humeral calli, which are sharply, nearly stepwise delimited mesally; elytral apices separately rounded. Punctures more distinct than those on head and pronotum but very small and shallow, unevenly distributed, separated by spaces 0.5–3 × as wide as diameters of punctures; setae sparse, long and erect.

Legs long and slender, unmodified.

Aedeagus ( Figs 4–7 ) stout, drop-shaped; AeL 0.35 mm; median lobe in ventral view broadest near middle and strongly narrowing distad, dorsal and ventral apical plates subtriangular with rounded apices, ventral plate flanked by a pair of elongate sclerites with their apices twisted laterad, dorsal plate in lateral view curved dorsad at an obtuse angle; parameres slender, their apices not reaching apex of ventral plate, each with one apical and one subapical seta.

Female. Unknown.

Distribution. Central Vietnam, Thừa Thiên-Huễ Province.

Etymology. Locotypical, after Mount Bach Ma.

Remarks. To date, only one species placed in Napochus was known to occur in Vietnam. Euconnus tuonglinhensis Franz, 1983 was described on the basis of four specimens, of which at least one, the holotype, is a male, and Franz did not mention any oddities in the antennal club. Moreover, E. tuonglinhensis has a distinctly different aedeagus, which was illustrated by Franz (1983) with a subrectangular apex, asymmetrical internal sclerites and the parameres much longer than those in E. bachmamontanus . No described species of Napochus are known to occur in Cambodia and Laos; and males of all species recorded from Thailand have unmodified antennae.

Before Neonapochus was synonymized with Napochus , a subgeneric placement of E. bachmamontanus would have been problematic. The only ' Napochus -like' species showing a distinct sexual dimorphism in the antennal structure was E. (Neonapochus) maklini ( Mannerheim, 1844) . However, in males of the latter species, antennomeres IX and X are asymmetrical, with the anteromesal region of each developed as a subtriangular projection directed distad (illustrated in Jałoszyński (2016)). There is no excavation, and the antennomere IX is transverse and smaller than X. Neither E. maklini , nor E. bachmamontanus differ in any other important structures from the type species of Napochus . The discovery of the new Vietnamese species supports the previous decision of placing Neonapochus as a synonym of Napochus (and thus extending the subgeneric diagnosis to include not only beetles with unmodified antennomeres, but also those with dimorphic antennae). Euconnus bachmamontanus demonstrates that the range of morphological diversity within Napochus is broader than that known to authors who gave original diagnoses of Neonapochus and Napochus . Species showing various modifications in males (cephalic structures, as in the former subgenus Cephaloconnus , or antennal characters, as in Neonapochus ) might have likely evolved from within Napochus , and not as components of any clade sister to it.

Figures

FIGURES 1–7. Euconnus bachmamontanus sp. n. Male holotype in dorsal view (1); antennal club in dorsal (2) and lateral (3) views; aedeagus in ventral (4, 6) and lateral (5, 7) views.