Arthromelodes latithorax, 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 : 43-45

Arthromelodes latithorax sp. nov.

( Figs 17 , 78C , 92C )

Chinese common name: Pḃnjà甲

Type material (6 exx.). HOLOTYPE: CHINA: ♂, ‘ China: Xizang, Nyalam County, Zhangmu Town (樟木W), 27°59’15”N, 85°58’59”E, 2250 m, leaf litter, sifted, 22.vii.2010, Jian-Qing Zhu leg.’ ( SNUC) . PARATYPES: CHINA: 3 ♀♀, same data as that of holotype; 2 ♀♀, same data as that of holotype except ‘ 27°57’21”N, 85°58’41”E, 27.vii.2010 ’ (all in SNUC) .

Diagnosis. Male. Body length over 2.1 mm. Head sub-rectangular at base; vertex with deep transverse sulcus between antennal tubercles and moderately long mediobasal carina, vertexal foveae moderately large and asetose; antenna elongate, lacking modifications; antennomeres 1–7 each slightly elongate, 8 smallest, 9 and 10 approximately subequal in width, 9 longer than 10, 11 slightly shorter than 9 and 10 combined. Discal stria of elytron thin and shallow, extending posteriorly to approximately apical 3/5 of elytral length. Fore and hind legs simple, mesotrochanter with short ventral spine, mesofemur strongly thickened, mesotibia with thickened, with large curved spine at apex. Abdomen lacking modifications, with large tergite 1 (IV) longer than tergites 2–4 (V–VII) combined. Aedeagus strongly asymmetric, median lobe relatively broad in dorsal view, dorsal lobe strongly elongate, ventral stalk strongly curved and with pointed apex, parameres reduced and forming single membranous structure. Female. Body length slightly over 2.0 mm, legs lacking modifications, genitalia as in Fig. 17I .

Description. Male. Body ( Fig. 17A ) length 2.16 mm; color reddish-brown, head and pronotum slightly darker than elytra and abdomen, tarsi and mouthparts lighter. Dorsal surface of body covered with dense long pubescence.

Head ( Fig. 17B ) sub-rectangular at base, wider than long, length 0.47 mm, width across eyes 0.52 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 25 large ommatidia. Antenna 1.16 mm long, lacking modifications; antennomere 1 thick, subcylindrical, 2–7 each elongate, 8 smallest, much shorter and narrower than 7, 9–10 successively shorter, subequal in width, 11 largest, slightly shorter than 9 and 10 combined, sub-fusiform.

Pronotum ( Fig. 17B ) slightly wider than long, length 0.58 mm, width 0.62 mm, widest at middle; lateral margins laterally expanded and rounded; disc weakly convex, finely punctate, with median longitudinal sulcus 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, anteriorly confluent with additional setose marginal sulcus, with punctiform lateral antebasal hypomeral pit; margin of coxal cavity weakly carinate.

Elytra much wider than long, length 0.76 mm, width 0.90 mm, narrowed at base; each elytron with two large basal foveae, lacking subbasal fovea; humeral angle rounded; discal stria extending from outer basal fovea to apical 3/5 of elytral length; 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 and hind legs simple. Mesotrochanter ( Fig. 17C ) with short, setose spine at base, mesofemur ( Fig. 17C ) strongly thickened, mesotibia ( Fig. 17D ) with large, curved spine at apex.

Abdomen as broad as elytra, widest at lateral margins of tergite 1 (IV), length 0.43 mm, width 0.90 mm, lacking modifications. Tergite 1 (IV) longer than tergites 2–4 (V–VII) combined; lacking basal sulcus\impression, with single mediobasal fovea (likely formed by medially moved ones) and one pair of basolateral foveae, lacking 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 single, large mediobasal and large, round basolateral foveae, with setose basal impression laterally, lacking 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. 17E ) slightly oval, moderately sclerotized, apical margin rounded.

Aedeagus ( Fig. 17F–H ) 0.53 mm long, strongly asymmetric; median lobe with moderately large basal capsule and slightly oval foramen, basoventral projection relatively long, ventral stalk long and in dorsal view broad and moderately curved; dorsal lobe elongate and gradually narrowing from base towards apex, strongly curved at apical portion, 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 2.05–2.23 mm; length/width of head 0.47–0.48/ 0.52–0.54 mm, pronotum 0.57–0.58/ 0.61–0.62 mm, elytra 0.73–0.75/ 0.91–0.96 mm; abdomen 0.45/ 0.87–0.94 mm; length of antenna 1.10–1.15 mm; maximum width of genitalia ( Fig. 17I ) 0.47 mm.

Comparative notes. Arthromelodes latithorax is a member of the A. championi group based on the unique form of the aedeagus. It is most similar to the sympatric A. zhangmu by sharing similar pronotal expansions, thickened male mesofemur, and mesotibia with a large apical spine. They can be differentiated by the more strongly expanded lateral margins of the pronotum, the more strongly curved mesotibia and apical spine, as well as by the dorsally much narrower ventral stalk of aedeagal median lobe of Arthromelodes latithorax . The new species also shares with the northern Indian A. planiceps the more or less laterally expanded tempora and pronotum, but can be readily separated by the male lacking a prominent humerus, the thickened mesofemur, and the mesotibia with a large, curved apical spine. Arthromelodes planiceps has a denticulate elytral humerus in the male, and lacks obvious sexual characters on the middle legs.

Distribution. Nyalam County, Tibet, SW China ( Figs 78C , 92C ).

Etymology. The species name is a combination of Latin ‘ latus, - a, - um ’ (wide, broad) and ‘ thorax ’, referring to the laterally expanded prothorax of the new species.

Figures

FIGURE 17. Morphology of Arthromelodes latithorax sp. nov. (A–H. Male. I. Female). A. Dorsal habitus. B. Head and pronotum. C. Mesotrochanter and mesofemur. D. Mesotibia. E. Sternite 7 (IX). F–H. Aedeagus, dorsal (F), lateral (G) and ventral (H). I. Genitalia. Scale bars: 0.5 mm in A; 0.3 mm in B–D; 0.1 mm in E, I; 0.2 mm in F–H.

FIGURE 78. Distribution of Tibetan Batrisini. A. Arthromelodes cylindricus sp. nov. (circle), A. flosculus sp. nov. (triangle) and A. gyamda sp. nov. (square). B. A. intricatus sp. nov. (circle), A. lage sp. nov. (triangle) and A. langjicuo sp. nov. (square). C. A. latithorax sp. nov. (circle), A. lebus sp. nov. (triangle) and A. lotus 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.