Arthromelodes markam, Yin, 2022

Yin, Zi-Wei, 2022, The Batrisini of Tibet: unveiling an enigmatic ant-loving beetle diversity at Earth’s “ Third Pole ” (Coleoptera, Staphylinidae, Pselaphinae), Zootaxa 5111 (1), pp. 1-211 : 49-51

Arthromelodes markam sp. nov.

( Figs 20 , 79A , 100F )

Chinese common name: Ẽ康njà甲

Type material (2 exx.). HOLOTYPE: CHINA: ♂ , ‘ China: Xizang (Chamdo City), Markam County, Juebashan Pass (29°33’8”N, 98°18’55”E), ca. 3900 m, 27.vi.2011, Wen-Xuan Bi leg., [ƱẪẼ康ẅ巴山垭口]’ ( SNUC) . PARATYPES: CHINA: 1 ♂, same data as that of holotype ( SNUC) .

Diagnosis. Male. Body length slightly over 2.2 mm. Head subtruncate at base; vertex with complete, reversed U-shaped sulcus connecting relatively small, asetose vertexal foveae; antenna long, antennomeres each slightly elongate, lacking modifications. Discal stria of elytron extending to approximately apical 1/5 of elytral length. Mesotrochanter with small ventral tubercle, mesotibia distinctly constricted before apex and with large apical spur; metafemur strongly clavate, basal third narrowed and then expanded for apical two-thirds. Abdomen with large tergite 1 (IV) longer than tergites 2–4 (V–VII) combined; tergite 1 (IV) with small central impression near posterior margin and pair of setose patches laterally. Aedeagus strongly asymmetric, ventral stalk of median lobe protruding and slightly curved, apex in dorsal view rounded, dorsal lobe broader than ventral stalk, parameres reduced and forming single membranous structure.

Description. Male. Body ( Fig. 20A ) length 2.22–2.27 mm; color light reddish-brown, tarsi and mouthparts paler. Dorsal surface of body covered with moderately long pubescence.

Head ( Fig. 20B ) subtruncate at base, slightly broader than long, length 0.42–0.43 mm, width across eyes 0.45 mm; vertex finely punctate, with relatively small, asetose vertexal foveae (dorsal tentorial pits), with complete, reversed U-shaped sulcus connecting foveae, mediobasal carina short, indistinct, antennal tubercles moderately raised; frons broadly and shallowly impressed medially, confluent with clypeus; clypeus with smooth surface, its anterior margin carinate and moderately raised; ocular-mandibular carina complete. Venter with two small gular foveae (posterior tentorial pits) originating from shared transverse opening, with thin median carina extending from fovea anteriorly to mouthparts. Compound eyes prominent, composed of approximately 30 relatively large ommatidia. Antenna lacking distinct club and modification, length 1.08–1.13 mm; antennomere 1 thick, subcylindrical, 2–11 each elongate, 11 largest, distinctly shorter than 9 and 10 combined, sub-fusiform.

Pronotum ( Fig. 20B ) approximately as long wide, length 0.45–0.47 mm, width 0.45 mm, widest at middle; lateral margins rounded; disc slightly convex, finely punctate, with median longitudinal sulcus slightly longer than lateral sulci in dorsal view; lacking median antebasal fovea, with complete transverse antebasal sulcus connecting lateral antebasal foveae; outer and inner pair of basolateral foveae distinct. Prosternum with anterior part approximately as long as coxal part, with small lateral procoxal foveae; hypomeral ridge present at basal 1/2, with indistinct lateral antebasal hypomeral pit; margin of coxal cavity weakly carinate.

Elytra much wider than long, length 0.64–0.66 mm, width 0.73–0.76 mm; each elytron with two medium-sized, asetose basal foveae, lacking subbasal fovea; humerus slightly prominent; discal stria extending from outer basal fovea to apical 1/5 of elytral length; subhumeral fovea present, marginal stria extending posteriorly from fovea to apex.

Mesoventrite short, demarcated from metaventrite by ridged anterior edges of impressed areas where large, setose lateral mesocoxal foveae situated at mesal margins, with pair of admesal carinae; setose median mesoventral foveae moderately separated, lateral mesoventral foveae large and setose, not forked internally. Metaventrite weakly impressed at middle, with pair of setose lateral metaventral foveae, posterior margin with small and narrow split at middle.

Legs elongate, fore legs simple. Mesotrochanter with small ventral tubercle, mesotibia ( Fig. 20C ) distinctly constricted before apex and with large apical spur; metafemur strongly clavate, basal third narrowed and then expanded for apical two-thirds.

Abdomen slightly narrower than elytra, widest at basolateral margins of tergite 1 (IV), length 0.65–0.67 mm, width 0.69–0.72 mm. Tergite 1 (IV) ( Fig. 20D ) strongly modified, with small central impression near posterior margin, posterior margin of cavity with small half-round tubercle, with several modified setae along anterior margin of impression, areas lateral to impression with large setose patches; setose basal sulcus separated by mediobasal and one pair of basolateral foveae, with very thin discal carinae; tergites 2–4 (V–VII) each with one pair of basolateral foveae, tergite 4 (VII) as long as 2 and 3 combined along middle, tergite 5 (VIII) semicircular, posterior margin roundly emarginate at middle. Sternite 2 (IV) lacking basal sulcus, with mediobasal and basolateral foveae and pair of short lateral carinae; midlength of sternite 2 (IV) shorter than 3–5 (V–VII) combined, sternites 3–5 approximately subequal in length along midline, each with one pair of tiny basolateral foveae, sternite 6 (VIII) transverse, posterior margin sinuate, sternite 7 (IX) ( Fig. 20E ) with weakly sclerotized, rounded apex and few long setae along apical margin.

Aedeagus ( Fig. 20F, G ) 0.34 mm long, strongly asymmetric; median lobe with large basal capsule and foramen, lacking distinct basoventral projection, ventral stalk strongly protruding and slightly curved ventrally, apex in dorsal view rounded; dorsal lobe elongate and broader than ventral stalk, narrowing apically; parameres reduced to single membranous structure.

Female. Unknown.

Comparative notes. This is a quite distinct species of which the males can be readily separated from those of all known congeners by the unique modification of the abdomen, the forms of the mesotibiae and metafemora, as well as the form of the aedeagus.

Distribution. Markam County, Tibet, SW China ( Figs 79A , 100F ).

Etymology. The new species is named after Markam County, where the type locality is situated.

Figures

FIGURE 20. Morphology of Arthromelodes markam sp. nov., male. A. Dorsal habitus. B. Head and pronotum. C. Mesotibia. D. Tergite 1 (IV). E. Sternite 7 (IX). F, H. Aedeagus, lateral (F) and ventral (G). Scale bars: 0.5 mm in A; 0.3 mm in B–D; 0.1 mm in E; 0.2 mm in F, G.

FIGURE 79. Distribution of Tibetan Batrisini. A. Arthromelodes markam sp. nov. (circle), A. monba sp. nov. (triangle) and A. nepaeformis sp. nov. (square). B. A. nepaeformis sp. nov. (circle), A. songxiaobini sp. nov. (triangle) and A. speciosus sp. nov. (square). C. A. torus sp. nov. (circle), A. zhangmu sp. nov. (triangle) and A. zhentangensis sp. nov. (square).

FIGURE 100. Environment of and collecting sites at Nyingchi area (A–E) and Chamdo (ăƀ) (F). A. 80K. B. 96K. C–E. Xiachayu (T察ø). F. pass of Jueba Mountain (ẅ巴山口), Markam (Ẽ康). Photo Credit: A by Zhong Peng; B by Xiao-Bin Song; F by Wen-Xuan Bi.