Arthromelodes monba, 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 : 51-53

Arthromelodes monba sp. nov.

( Figs 21 , 79A , 95A, B )

Chinese common name: Ḣ巴njà甲

Type material ( 1 ex.). HOLOTYPE: CHINA: ♂, ‘ China: Xizang, Cona County, Lebu Valley , pass to Mama Vill., 27°50’16”N, 91°45’48”E, 2400–2700 m, 04.vii.2021, Z. Peng, Z. Yin & W. Zhang leg., ƱẪDZḄ县勒布沟Þ玛 乡 ’ ( SNUC).

Diagnosis. Male. Body length approximately 2.2 mm. Head subtruncate at base; vertex with deep transverse sulcus between antennal tubercles and long mediobasal carina, vertexal foveae moderately large and asetose; antenna moderately elongate, antennomeres slightly elongate or as long as wide, lacking modifications. Discal stria of elytron extending to apical 1/4 of elytral length. Fore and hind legs simple, mesotrochanter with apically setose protuberance on ventral margin, mesofemur with short spine at distal 1/3, mesotibia with tufted setae at apical 1/3 and long apical spine. Abdomen with large Tergite 1 (IV) longer than tergites 2–4 (V–VII) combined in dorsal view, tergites 1 (IV) prominent at middle. Aedeagus strongly asymmetric, median lobe in dorsal view markedly broad through length, dorsal lobe extremely elongate, strongly curved downwards apically, parameres reduced and forming single membranous structure.

Description. Male. Body ( Fig. 21A ) length 2.21 mm; color reddish-brown, tarsi and mouthparts lighter. Dorsal surface of body covered with short pubescence.

Head ( Fig. 21B ) subtruncate at base, approximately as long as wide, length 0.45 mm, width across eyes 0.44 mm; vertex finely punctate, with moderately large, asetose vertexal foveae (dorsal tentorial pits), with deep, slightly curved transverse sulcus between antennal tubercles, distinct mediobasal carina extending from near head base anteriorly to sulcus, 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 foveae (posterior tentorial pits) in single small round opening, with distinct median carina extending from fovea anteriorly to mouthparts. Compound eyes prominent, composed of approximately 30 moderately large ommatidia. Antenna 1.10 mm long, club formed by moderately enlarged apical three antennomeres; antennomere 1 thick, subcylindrical, 2–7 each elongate, with 5–7 much longer than neighboring antennomeres, 8 smallest, 9 much larger than 8, 10 as wide as and slightly shorter than 9, 11 largest, simple, approximately as long as 9 and 10 combined, sub-conical.

Pronotum ( Fig. 21B ) approximately as long as wide, length 0.50 mm, width 0.48 mm, widest at middle; lateral margins rounded; disc moderately convex, finely punctate, with median longitudinal sulcus slightly longer than semicircular lateral sulci in dorsal view; lacking median antebasal fovea, with complete, deep transverse antebasal sulcus connecting lateral antebasal foveae; outer and inner pair of basolateral foveae distinct. Prosternum with anterior part slightly longer than coxal part, with small lateral procoxal foveae; hypomeral ridge present at basal 1/2, with lateral antebasal impression; margin of coxal cavity weakly carinate.

Elytra much wider than long, length 0.71 mm, width 0.80 mm; each elytron with two large, widely separated basal foveae, lacking subbasal fovea; humerus roundly prominent; discal stria extending from outer basal fovea to apical 1/4 of elytral length; subhumeral fovea small, 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 in transverse opening, broadly separated, lateral mesoventral foveae large and setose, not forked internally. Metaventrite broadly and shallowly impressed at middle, with pair of setose lateral metaventral foveae, posterior margin with small and narrow split at middle. Longitudinal marginal ridge of meso- and metaventrite complete.

Legs elongate, fore and hind legs simple. Mesotrochanter ( Fig. 21C ) with short, apically setose ventral spine, mesofemur ( Fig. 21C ) with short, apically curved spine at distal 1/3, mesotibia ( Fig. 21D ) with acute tuft of setae at apical 1/3, then strongly narrowing apically and with long, curved blade-like spine at apex.

Abdomen slightly narrower than elytra, widest at basolateral margins of tergite 1 (IV), length 0.66 mm, width 0.67 mm; with first dorsally visible tergite modified. Tergite 1 (IV) ( Fig. 21E ) longer than tergites 2–4 (V–VII) combined; with moderately large, round projection at middle of posterior margin, transverse area lateral to projection covered with dense, short setae, setose basal sulcus separated by broadly separated mediobasal and one pair of basolateral foveae, lacking discal carinae; tergites 2–3 (V–VII) lacking foveae or lateral carinae, tergite 4 (VII) as long as 2 and 3 combined along middle, with pair of complete lateral carinae, tergite 5 (VIII) semicircular, posterior margin roundly emarginate at middle. Sternite 2 (IV) with large mediobasal and broad basolateral foveae, lacking lateral carinae; midlength of sternite 2 (IV) slightly longer than sternites 3–5 (V–VII) combined, 3–5 each with one pair of tiny basolateral foveae, sternite 6 (VIII) transverse, posterior margin sinuate, sternite 7 (IX) ( Fig. 21F ) slightly oval, moderately sclerotized, with scattered long setae along apical margin.

Aedeagus ( Fig. 21G, H ) 0.39 mm long, strongly asymmetric; median lobe with large basal capsule and rounded triangular foramen, basoventral projection moderately long, ventral stalk in dorsal view markedly broad though entire length, in ventral view narrowing from base toward apex; dorsal lobe extremely elongate and strongly curved downwards at apex, gradually narrowing from base towards apex; parameres reduced to single membranous structure.

Female. Unknown.

Comparative notes. The new species belongs to a group of species centered on A. championi that bear a long apical spine of the mesotibia, and a strongly elongate and strongly curved dorsal lobe of the aedeagus. The male of Arthromelodes monba can be readily separated by the presence of an acute setose tuft of mesotibia, a spinose mesofemur, a unique form of tergal modification, as well as a dorsally markedly broad median lobe of the aedeagus.

Distribution. Cona County, Tibet, SW China ( Figs 79A , 95A, B ).

Etymology. The new species is named after the local Monba people (Ḣ巴⁂).

Figures

FIGURE 21. Morphology of Arthromelodes monba sp. nov., male. A. Dorsal habitus. B. Head and pronotum. C. Mesotrochanter and mesofemur. D. Mesotibia. E. Tergite 1 (IV). F. Sternite 7 (IX). G, H. Aedeagus, lateral (G) and ventral (H). Scale bars: 0.5 mm in A; 0.3 mm in B; 0.2 mm in C–E; 0.05 mm in F, 0.2 mm in G, H.

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 95. Environment of and collecting sites at Lebu Valley (勒布沟). Forests at 2400 m (A, B), and 3650 m (C, D).