Arthromelodes zhangmu, 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 : 64-65

Arthromelodes zhangmu sp. nov.

( Figs 27 , 79C , 92C )

Chinese common name: 樟木njà甲

Type material (7 exx.). HOLOTYPE: CHINA : ♂, ‘ China: Xizang, Nyalam County, Zhangmu Town (樟木W), 27°59’15”N, 85°58’59”E, 2200 m, leaf litter, sifted, 17.vii.2010, Jian-Qing Zhu leg.’ ( SNUC) . PARATYPES: CHINA: 2 ♂♂, 2 ♀♀, same locality as holotype, except ‘ Lixin Village (ĒẾ村), 27°57’21”N, 85°58’41”E, 2400– 2600 m, 27.vii.2010 ’; 1 ♂, same locality, except ‘ 2600 m, 18.vii.2010 ’; 1 ♀, same locality, except ‘ 27°59’15”N, 85°58’59”E, 2250 m, 22.vii.2010 ’ (all paratypes in SNUC) .

Diagnosis. Male. Body length over 2.47–2.64 mm. Head sub-rectangular at base; vertex with deep transverse sulcus between antennal tubercles and long mediobasal carina, vertexal foveae moderately large and asetose; antenna elongate, lacking modifications; antennomeres each slightly elongate, 8 shortest, 9 and 10 approximately subequal in width, 9 longer than 10, 11 much shorter than 9 and 10 combined. Discal stria of elytron thin and shallow, extending posteriorly to approximately apical 1/5 of elytral length. Fore legs simple, mesotrochanter with short ventral spine, mesofemur moderately thickened, mesotibia with large apical, metatrochanter with lamellar projection. Abdomen lacking modifications, with large tergite 1 (IV) longer than tergites 2–4 (V–VII) combined. Aedeagus strongly asymmetric, median lobe in dorsal view broad, dorsal lobe strongly elongate, ventral stalk strongly curved and with pointed apex, parameres reduced and forming single membranous structure. Female. Body length slightly over 2.24–2.39 mm, legs lacking modifications, genitalia as in Fig. 27I .

Description. Male. Body ( Fig. 27A ) length 2.47–2.64 mm; color reddish-brown, tarsi and mouthparts lighter. Dorsal surface of body covered with dense, moderately long pubescence.

Head ( Fig. 27B ) sub-rectangular at base, wider than long, length 0.50–0.52 mm, width across eyes 0.51–0.54 mm; vertex finely punctate, with relatively large, asetose vertexal foveae (dorsal tentorial pits), with deep, curved transverse sulcus between antennal tubercles, mediobasal carina extending from near head base anteriorly to sulcus, antennal tubercles weakly prominent; frons almost flat, confluent with clypeus; clypeus with smooth surface, its anterior margin carinate and moderately raised; ocular-mandibular carina complete. Venter with single gular fovea (posterior tentorial pit), with distinct median carina extending from fovea anteriorly to mouthparts. Compound eyes prominent, composed of approximately 35 large ommatidia. Antenna 1.20–1.26 mm long, lacking modifications; antennomere 1 thick, subcylindrical, 2–11 each elongate, 8 smallest, slightly shorter and narrower than 7, 9–10 successively shorter and broader, 11 largest, much shorter than 9 and 10 combined, sub-fusiform.

Pronotum ( Fig. 27B ) slightly wider than long, length 0.55–0.60 mm, width 0.55–0.59 mm, widest at middle; lateral margins moderately expanded and rounded; disc weakly 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 distinct lateral procoxal foveae; hypomeral ridge present at basal 1/2, extending from base to middle of anterior part, with punctiform lateral antebasal hypomeral pit; margin of coxal cavity weakly carinate.

Elytra much wider than long, length 0.76–0.80 mm, width 0.90–0.98 mm, narrowed at base; each elytron with two large basal foveae, lacking subbasal fovea; humerus weakly prominent; discal stria extending from outer basal fovea to apical 1/5 of elytral length; small subhumeral fovea present, thin marginal stria extending posteriorly from fovea to posterior margin of elytron.

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 broadly separated, lateral mesoventral foveae large and setose, not forked internally. Metaventrite slightly 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 ( Fig. 27C ) with short ventral spine at base, mesofemur moderately thickened, mesotibia ( Fig. 27D ) with large spine at apex, metatrochanter ( Fig. 27E ) with truncate, lamellar projection on ventral margin.

Abdomen as broad as elytra, widest at lateral margins of tergite 1 (IV), length 0.67–0.73 mm, width 0.84–0.89 mm, lacking modifications. Tergite 1 (IV) longer than tergites 2–4 (V–VII) combined; broadly separated mediobasal fovea and one pair of basolateral foveae separating basal sulcus, with pair of short discal carinae; tergites 2 and 3 (V and VI) each short, tergite 4 (VII) approximately as long as 2 and 3 combined along middle, tergites 2–4 (V–VII) each with one pair of small basolateral foveae, tergite 5 (VIII) semicircular, posterior margin roundly emarginate at middle. Sternite 2 (IV) with large mediobasal foveae and large basolateral sockets, with setose basal impression laterally, with pair of basolateral carinae; midlength of sternite 2 (IV) approximately as long as 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. 27F ) slightly oval, moderately sclerotized, apical margin rounded.

Aedeagus ( Fig. 27G, H ) 0.42 mm long, strongly asymmetric; median lobe with moderately large basal capsule and elongate foramen, basoventral projection relatively large, ventral stalk long and broad in dorsal view; dorsal lobe elongate and gradually narrowing from middle towards apex, apical part strongly curved ventrally, with pointed apex; parameres reduced to single membranous structure.

Female. Similar to male in external morphology; legs lacking modifications; each compound eye composed of approximately 18 ommatidia; humeral angle rounded. Measurements (as for male): body length 2.24–2.39 mm; length/width of head 0.48–0.49/ 0.49–0.50 mm, pronotum 0.52–0.53/ 0.50–0.51 mm, elytra 0.60–0.66/ 0.83–0.88 mm; abdomen 0.63–0.64/ 0.75–0.81 mm; length of antenna 1.17–1.19 mm; maximum width of genitalia ( Fig. 27I ) 0.29 mm.

Comparative notes. The new species is morphologically most similar to the sympatrically distributed A. latithorax , sharing the laterally expanded pronotal margins, the thickened mesofemur, and a large apical spine of the mesotibia. These two species can be readily separated by the lesser expansion of the pronotal lateral margins, the less curved mesotibia and apical spine, a dorsally much broader ventral lobe of the aedeagus, and the different structure of the female genitalia.

Distribution. Nyalam County, Tibet, SW China ( Figs 79C , 92C ).

Etymology. The new species is named after its type locality, i. e., Zhangmu Town.

Figures

FIGURE 27. Morphology of Arthromelodes zhangmu sp. nov. (A–H. Male. I. Female). A. Dorsal habitus. B. Head and pronotum. C. Mesotrochanter. D. Mesotibia. E. Metatrochanter. F. Sternite 7 (IX). G, H. Aedeagus, dorsal (G) and lateral (H). I. Genitalia. Scale bars: 0.5 mm in A; 0.3 mm in B; 0.2 mm in C–E; 0.05 mm in F, I, 0.1 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 92. Environment of Zhangmu Valley (樟木沟). Environment of Youyiqiao (友谊桥) (A, B), Lixin Village (ĒẾ村) (C) and Qu Township (DZ乡) (D). Photo Credit: A, B by Jian-Qing Zhu; C, D by Wen-Xuan Bi.