Stenichnus (Stenichnus) bifurcatus Jałoszyński 2023, sp. n.
Creators: name: Jałoszyński, Paweł
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Staphylinidae
Stenichnus
Stenichnus bifurcatus

description: Stenichnus (Stenichnus) bifurcatus sp. n.
(Figs 1–5)
Type material studied. Holotype (TAIWAN): ♁, two labels: “TAIWAN Taichung / Hsien, Anmashan / 2225m 2.V.1990 / A. Smetana [T38]” [white, printed], “ STENICHNUS (s. str.) \ bifurcatus m. \ P. Jałoszyński, 2023 \ HOLOTYPUS ” [red, printed] (MHNG). Paratypes (2 exx.): 1 ♁, 1 ♀, “TAIWAN Nantou / Hsien, Meifeng / 2130m 12.V.1991 / A.Smetana [T78]” (paratypes with yellow “ PARATYPUS ” labels, deposited in MHNG and cPJ).
Diagnosis. Body length exceeding 2.2 mm; base of pronotum with transverse row of 8–10 slightly unevenly distributed small pits interrupted at middle by distinct impunctate gap; punctures on head and pronotum inconspicuous, fine, on elytra distinct but shallow and with diffuse margins; profemur in male unmodified; antennae in both sexes with antennomere 11 much shorter than 9 and 10 combined and 1.6–1.7 times as long as broad; aedeagus in ventral view with bifurcate apex and with pair of unbranched lateral rod-like sclerites curved mesally.
Description. Body of male (Fig. 1) strongly convex, dark brown with distinctly lighter tarsi and palps, covered with setae slightly lighter than cuticle; BL 2.25–2.30 mm.
Head broadest at eyes, HL 0.38–0.40 mm, HW 0.45–0.48 mm; tempora in dorsal view slightly shorter than eyes and evenly rounded, strongly converging posteromesally; vertex and frons confluent, together weakly convex; each eye strongly convex, slightly oval, finely faceted. Punctures on vertex and frons fine, inconspicuous; setae short, sparse and suberect. Antennae slender, AnL 1.13 mm, antennomeres 1–8 each elongate, 9 as long as broad, 10 indistinctly transverse, 11 much shorter than 9 and 10 combined, 1.6–1.7 times as long as broad.
Pronotum broadest near anterior fourth; PL 0.60 mm, PW 0.60 mm. Anterior margin broadly rounded, anterior corners not marked, broadly rounded, so that anterior and lateral margins are confluent, lateral margins strongly rounded in anterior half, posteriorly weakly sinuate; posterior corners obtuse-angled, blunt; posterior margin weakly arcuate. Base of pronotum with transverse row of 8–10 slightly unevenly distributed small pits disrupted at middle by distinct gap. Punctures on pronotal disc as inconspicuous as those on frons and vertex, setae moderately long, sparse and erect.
Elytra together oval, broadest clearly in front of middle; EL 1.25–1.33 mm, EW 1.00 mm, EI 1.25–1.33; humeral calli distinct but weakly demarcated from disc, basal impression on each elytron large, deep, nearly circular; elytral apices separately rounded. Punctures much more distinct than those on head and pronotum but small, shallow and with diffuse margins, those on anterior half of elytra separated by spaces subequal to diameters of punctures; setae thicker and longer than those on head and pronotum, moderately dense, erect.
Legs long and slender, unmodified.
Aedeagus (Figs 2–5) in ventral view stout, with basal capsular region much longer than apical portion, which is rapidly narrowed and bearing deep median rounded emargination, so that apex of aedeagus forms pair of rounded lateral lobes; diaphragm oval, adjacent to base of median lobe; ventral wall with pair of lateral projections with rounded apices; endophallus with pair of permanently everted lateral sclerites curved toward midline of median lobe; parameres not reaching apex of median lobe, each slightly broadened in apical region and bearing several apical and subapical setae of various lengths. AeL 0.48 mm.
Female. Externally indistinguishable from male. BL 2.25 mm; HL 0.40 mm, HW 0.48 mm, AnL 1.13 mm; PL 0.60 mm, PW 0.65 mm; EL 1.25 mm, EW 0.98 mm, EI 1.28.
Distribution. Taiwan.
Etymology. The adjective bifurcatus refers to the bifurcate aedeagal apex.
Remarks. Adults of this species are among the largest Stenichnus of Eastern Palaearctic, and externally resemble S. totoro (Jałoszyński 2004), and, to a lesser extent, the newly described (and slightly smaller) S. totoroides (see below). These three species may be closely related; they share a pair of lateral apical endophallic sclerites projecting from the ostium, a feature unique within Stenichnus. They clearly differ in the general shape of the median lobe, and especially its apex (bifurcate in S. bifurcatus (Fig. 2), subtriangular in S. totoroides (Fig. 7), and truncate in S. totoro (Fig. 12)), and in the shape of the lateral apical sclerites (unbranched in S. bifurcatus and S. totoroides, and each with a short outer branch in S. totoro).
Stenichnus taiwanensis (Franz, 1985) from Taiwan, known from a single female, is also a large-bodied species externally similar to S. totoro, and therefore also to S. bifurcatus. However, the holotype female of S. taiwanensis has the antennomere 11 nearly as long as 9 and 10 combined, almost twice as long as broad (illustrated in Jałoszyński (2004): fig. 2C), while in S. bifurcatus the antennomere 11 is much shorter than 9 and 10 combined and only 1.6–1.7 times as long as broad.
description: Published as part of Jałoszyński, Paweł, 2023, New species and new records of Eastern Palaearctic Stenichnus Thomson (Coleoptera, Staphylinidae, Scydmaeninae), pp. 363-381 in Zootaxa 5318 (3) on pages 364-366, DOI: 10.11646/zootaxa.5318.3.3, http://zenodo.org/record/8167067