Siamites langkatensis, Jałoszyński, 2020

Jałoszyński, Paweł, 2020, Four new species of the Oriental genus Siamites Franz (Coleoptera, Staphylinidae Scydmaeninae), Zootaxa 4751 (1), pp. 187-195 : 188

Siamites langkatensis sp. n.

( Figs 1–6 )

Type material. Holotype: INDONESIA (Sumatra): ♂, two labels: “ SUMATRA / res. Langkat / bord Bohorok-5. / J.Robert-VII.84” [white, printed]; “ SIAMITES / langkatensis m. / det. P. Jałoszyński, 2020 / HOLOTYPUS ” [red, printed] ( MHNG).

Diagnosis. Male macrophthalmous; head with six separate tufts of bristles evenly distributed along posterior margin of vertex; aedeagus broadest near middle, with deeply bifurcate apical region.

Description. Body of male ( Fig. 1 ) moderately convex and moderately slender, uniformly light brown, covered with yellowish vestiture. BL 1.10 mm.

Head ( Fig. 2 ) broadest at conspicuously large, strongly convex and coarsely faceted eyes, HL 0.15 mm, HW 0.23 mm; tempora in dorsal view nearly as long as eyes; vertex flattened at middle, strongly transverse; frons confluent with vertex, with shallow median impression between weakly elevated supraantennal tubercles. Punctures on vertex obscured by bristles, those on frons fine, inconspicuous. Vestiture of head dorsum ( Fig. 2 ) composed of six separate tufts of dense bristles forming a transverse row on vertex; long and moderately thick bristles directed posterodorsad and situated slightly in front of posterior tufts; and sparse, suberect setae on frons. Antennae short, with moderately broadened, indistinctly delimited tetramerous club, AnL 0.45 mm; scape and pedicel strongly elongate; antennomeres III–VI each indistinctly elongate, VII about as long as broad, VIII–X each distinctly transverse, XI distinctly shorter than IX–X combined, narrower than X, indistinctly elongate.

Pronotum subconical with broad anterior margin, broadest near posterior third; PL 0.30 mm, PW 0.28 mm. All margins weakly and evenly rounded; lateral carinae distinct and almost as long as half length of pronotum; base with distinct transverse groove deepened at each end. Punctures on pronotum fine and sparse, unremarkable; setae sparse, suberect, moderately long.

Elytra slightly flattened, together oval, broadest distinctly in front of middle; EL 0.65 mm, EW 0.48 mm, EI 1.37; humeral calli weakly marked, each with indistinct, rounded humeral carina not exceeding 1/4 of elytral length; basal impressions shallow and short; apices of elytra rounded together. Punctures on elytra more distinct and denser than those on pronotum but superficial and unremarkable; setae sparse, short, suberect.

Wings long and functional.

Aedeagus ( Figs 3–6 ) moderately stout; AeL 0.15 mm; median lobe fusiform, broadest near middle and strongly narrowing toward base and apex, apical region bifurcate, with two pairs of long lateral projections; endophallic structures lightly sclerotized; parameres short and moderately broad, each with two tiny apical setae.

Female. Unknown.

Distribution. Northern Sumatra ( Fig. 25 ).

Etymology. After the Indonesian regency of Langkat.

Remarks. Adults of Siamites are externally uniform; differences can be seen in proportions of body parts, distribution of tufts of bristles on the vertex, and a relative diameter of eyes. However, these differences can be indistinct, and the most reliable way to identify a species is to examine the aedeagus. The aedeagi in Siamites show far greater diversity than any external adult structures. Siamites langkatensis clearly differs from all congeners in the uniquely shaped, bifurcate apical region of the median lobe.

Figures

FIGURE 25. Distribution of nominal Siamites species.

FIGURES 1–6. Siamites langkatensis sp. n., dorsal habitus (1); head in anterodorsal view (2); aedeagus in ventral (3, 5) and lateral (4, 6) views.