Siamites sarawakensis, Jałoszyński, 2019

Jałoszyński, Paweł, 2019, The first species of Siamites Franz (Coleoptera, Staphylinidae, Scydmaeninae) in East Malaysia, Zootaxa 4545 (3), pp. 447-450 : 448

Siamites sarawakensis sp. n. ( Figs. 1–7 )

Type material. Holotype: MALAYSIA (Sarawak): ♂, two labels: "E. MALAYSIA: Sarawak / confl. Suan Oyan and / Mujong riv., E.Kapit / 150m, 19.V.1994, # 6a / Löbl & Burckhardt" [white, printed]; " SIAMITES / sarawakensis m. / det. P. Jałoszyński, 2018 / HOLOTYPUS " [red, printed] (MHNG).

Diagnosis. Male macrophthalmous; aedeagus pear-shaped; subapical endophallic plate with concave lateral and distal margins.

Description. Body of male ( Fig. 1 ) strongly convex and moderately slender, uniformly light brown, covered with yellowish vestiture. BL 1.16 mm.

Head ( Fig. 2 ) broadest at large, strongly convex and coarsely faceted eyes, HL 0.21 mm, HW 0.23 mm; tempora in lateral and dorsal view as long as eyes; vertex strongly impressed at middle, strongly transverse; frons confluent with vertex, with shallow median longitudinal impression; supraantennal tubercles weakly marked. Punctures on vertex obscured by bristles, those on frons very fine, inconspicuous. Vestiture of head dorsum ( Figs 1–2 ) composed of four large tufts of dense bristles forming a transverse arc on vertex, lateral pairs are so close to each other that appear as one transverse group of bristles, median asetose area between bristles relatively broad; additionally vertex at each side and tempora with long and sparse erect bristles flanking the tufts, and frons with thin, sparse and suberect setae. Antennae ( Fig. 1 ) short, with strongly broadened tetramerous club, AnL 0.45 mm; scape and pedicel strongly elongate; antennomeres III–V and VII each about as long as broad, VI indistinctly elongate, VIII–X each strongly transverse, XI slightly narrower than X, slightly longer than broad.

Pronotum semioval, broadest in posterior third but indistinctly narrowing posterad; PL 0.30 mm, PW 0.30 mm. Anterior and posterior margins weakly arcuate; sides nearly evenly rounded; pronotum with distinct carinate but relatively blunt lateral edges in posterior 3/4 and arcuate transverse ante-basal groove distinctly deepened at each end. Punctures on pronotum fine and sparse, unremarkable; setae sparse, suberect to erect, moderately long.

Elytra slightly flattened, oval, broadest distinctly in front of middle; EL 0.65 mm, EW 0.45 mm, EI 1.44; humeral calli weakly marked, each with indistinct humeral carina not exceeding 1/4 of elytral length; basal impressions shallow and short; apices of elytra separately rounded. Punctures on elytra slightly more distinct than those on pronotum but superficial and inconspicuous; setae sparse, short, suberect.

Aedeagus ( Figs 3–6 ) stout and small; AeL 0.09 mm; median lobe pear-shaped, broadest near distal third, with sinuate sides and rounded apical margin; internal sclerotization simple, with subapical endophallic plate-like structure, its sides and distal margin concave; parameres short and broad, each with five apical setae.

Female. Unknown.

Distribution. Central-northern Borneo ( Fig. 7 ).

Etymology. Locotypical, after the Malaysian state of Sarawak.

Remarks. Adults of Siamites species are morphologically relatively uniform and only males of S. deharvengi are conspicuous by having vestigial eyes, whereas males of all remaining species are macrophthalmous. Consequently, the aedeagus must be examined to identify species, and male genital organs within this small genus show greater diversity of shapes than externally visible structures of adults ( Fig. 7 ). The aedeagi of S. loebli , S. deharvengi and S. sarawakensis are relatively simple, but they clearly differ in ventral view in the shape of median lobe and endophallic structures. The aedeagus of S. complicatus is strikingly complex, with a pair of distolateral corkscrew-like projections and a very large, darkly sclerotized endophallus; none of the remaining species has similar structures. The aedeagus of S. loebli is conspicuously stout and has a distinctly bisinuate distal margin; the aedeagus of S. deharvengi is more slender, with distal margin truncated; and the aedeagus of S. sarawakensis is drop-shaped, with the distal margin rounded.

Siamites sarawakensis was found over 1200 km southeast of the collecting site of S. deharvengi and over 1500 km SE of the collecting site of S. complicatus ; this discovery significantly broadens the known distribution of Siamites .

A variously distinctly delimited trimerous club was included in the diagnosis of Siamites by Jałoszyński (2013). As the antennomere VIII in all species is broader than VII and narrower than IX, the club can be rather subjectively interpreted as tri- or tetramerous, depending on the width difference between antennomeres VII and VIII. In S. sarawakensis the club is relatively strongly broadened and clearly tetramerous; the diagnosis of Siamites is here emended to include species with tri- and tetramerous antennal clubs.

Figures

FIGURES 1–7. Siamites sarawakensis sp. n., dorsal habitus of holotype male (1); head in anterior view (2); aedeagus in ventral (3, 5) and lateral (4, 6) views; and distribution of nominal Siamites species illustrated with their aedeagi in ventral view (7).