Arthromelodes complexus, 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 : 21-23

Arthromelodes complexus sp. nov.

( Figs 7 , 77B , 93A–C )

Chinese common name: Ắúnjà甲

Type material (9 exx.). HOLOTYPE: CHINA: ♂ , ‘ China: Xizang, Dinggyê County, pass to Zhêntang Town , 27°54’15”N, 87°32’21”E, 3650–4020 m, 27.vi.2021, Peng, Yin & Zhang, ƱẪŤĠ县ĿƋ沟Ḃ山矮杜ḁff ’ ( SNUC) . PARATYPES: CHINA: 2 ♂♂, 1 ♀, same data as that of holotype; 1 ♂, 4 ♀♀, same data as that of holotype except ‘ 27°53’58”N, 87°27’21”E, 3060 m, 28.vi.2021, Yin & Zhang leg., ƱẪŤĠ县ĿƋ沟公ḡṅðff ’ (all paratypes in SNUC) .

Diagnosis. Male. Body length over 2.5 mm. Head subtruncate at base; vertex with V-shaped sulcus between antennal tubercles and long mediobasal carina, vertexal foveae relatively small and asetose; antenna elongate, lacking modifications; antennomeres each slightly elongate, 5–7 markedly long, 8 smallest, 11 approximately as long as 9 and 10 combined. Discal stria of elytron thin and shallow, extending posteriorly to apical 2/5 of elytral length. Hind legs simple, protrochanter with small ventral spine, protibia slightly emarginate at apical 1/3, mesotrochanter with apically setose protuberance on ventral margin, mesotibia with thin, curved apical spine.Abdomen with large tergite 1 (IV) longer than tergites 2–4 (V–VII) combined; tergite 1 with broad, bifid protuberance at middle, followed by central cavity and large tubercle at base. Aedeagus strongly asymmetric, median lobe with large basal capsule and elongately oval foramen, ventral stalk broad and dilated at apex, dorsal lobe elongate, forked at apex, parameres reduced and forming single membranous structure. Female. Body length over 2.5 mm, legs and abdomen lacking modifications, genitalia as in Fig. 7J .

Description. Male. Body ( Fig. 7A ) length 2.55–2.58 mm; color reddish-brown, tarsi and mouthparts slightly lighter. Dorsal surface of body covered with short pubescence.

Head ( Fig. 7B ) subtruncate at base, approximately as long as wide, length 0.55–0.56 mm, width across eyes 0.54 mm; vertex finely punctate, with relatively small, asetose vertexal foveae (dorsal tentorial pits), with distinct, V-shaped transverse sulcus between antennal tubercles, 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 tiny gular foveae (posterior tentorial pits) in single small pit, median carina extending before fovea anteriorly to mouthpart, gradually thickened anteriorly. Eyes moderately prominent, composed of approximately 27 ommatidia. Antenna 1.41–1.43 mm long, lacking modifications; antennomere 1 thick, subcylindrical, 2–8 each elongate, 5–7 markedly longer than neighboring ones, 3 and 8 of same length, shortest, 9 slightly longer but narrower than 10, 11 largest, approximately as long as 9 and 10 combined, sub-fusiform.

Pronotum ( Fig. 7B ) slightly longer than wide, length 0.62–0.64 mm, width 0.60–0.61 mm, widest at middle; lateral margins rounded; disc moderately convex, finely punctate, with median longitudinal sulcus slightly shorter than 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 punctiform lateral antebasal hypomeral pit; margin of coxal cavity weakly carinate.

Elytra much wider than long, length 0.86–0.87 mm, width 0.87–0.89 mm, constricted at bases; each elytron with two moderately-sized, widely separated basal foveae, lacking subbasal fovea; humeral angle rounded; discal stria extending from outer basal fovea posteriorly to apical 2/5 of elytral length; subhumeral fovea absent, thin marginal stria extending posteriorly from approximately basal 1/3 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 broadly impressed at middle, with pair of setose lateral metaventral foveae, posterior margin with long, narrow split at middle.

Legs elongate, hind legs simple. Protibia ( Fig. 7C ) broadly emarginate on mesal margin for apical 1/3, protrochanter with small ventral spine; mesotrochanter ( Fig. 7D ) with short, apically setose protuberance on ventral margin, mesotibia ( Fig. 7E ) with thin, curved spine at apex.

Abdomen slightly narrower than elytra, widest at lateral margins of tergite 1 (IV), length 0.57–0.64 mm, width 0.71–0.74 mm; with modified tergite 1 (IV). Tergite 1 ( Fig. 7F ) dorsally longer than tergites 2–4 (V–VII) combined, with broad, strongly raised projection at middle, projection with acute posterolateral angles, with transverse cavity posterior to projection, followed by large posteromedial tubercle, posterolateral areas devoid of setae, glabrous, basal impression broken by mediobasal and two pairs of basolateral foveae, with pair of short, thick, triangular discal carinae, with incomplete outer marginal carina; tergites 2 and 3 (V and VI) subequal in length and 4 (VII) slightly longer than 2 and 3 combined along middle, 2–4 (V–VII) each with one pair of small basolateral foveae, lateral carina of tergites 2 and 3 short, 4 complete, 5 (VIII) semicircular, posterior margin roundly emarginate at middle. Sternite 2 (IV) with two mediobasal foveae and large basolateral sockets, lacking basal impression or sulcus, with pair of short lateral carinae; midlength of sternite 2 (IV) slightly longer than 3–5 (V–VII) combined, 3–5 each with one pair of tiny basolateral foveae, sternite 6 (VIII) transverse, posterior margin broadly emarginate, sternite 7 (IX) ( Fig. 7G ) slightly oval, moderately sclerotized, apex rounded and with few long setae along apical margin.

Aedeagus ( Fig. 7H–I ) 0.36 mm long, strongly asymmetric; median lobe with large basal capsule and elongately oval foramen, basoventral projection short, ventral stalk protruding, in lateral view strongly dilated at apex; dorsal lobe obliquely erect, apically forked into two lobes; parameres reduced to single membranous structure.

Female. Similar to male in external morphology; antenna shorter; legs and abdomen lacking spines/projections or modifications; each compound eye composed of approximately 20 ommatidia; humeral angle rounded. Measurements (as for male): body length 2.51–2.54 mm; length/width of head 0.53/ 0.50–0.53 mm, pronotum 0.59–0.60/ 0.57–0.58 mm, elytra 0.80–0.82/ 0.86–0.87 mm; abdomen 0.64–0.70/ 0.75–0.76 mm; length of antenna 1.23–1.30 mm; maximum width of genitalia ( Fig. 7J ) 0.26 mm.

Comparative notes. Arthromelodes complexus is closest to A. alpitorus , A. langjicuo and A. torus by sharing a setose mesotrochanter, similar placement of the male tergal modification and form of the aedeagus. Arthromelodes complexus can be separated from these congeners by the unique emargination of the male protibia, and the structure of the modified male tergite 1 (IV).

Distribution. Dinggyê County, Tibet, SW China ( Figs 77B , 93A–C ).

Etymology. The new species epithet ‘ complexus (complex)’ is a Latin noun referring to the complicated modification of male tergite 1 (IV).

Figures

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

FIGURE 77. Distribution of Tibetan Batrisini. A. Arthromelodes alpitorus sp. nov. (circle), A. angulatus sp. nov. (triangle) and A. aniqiao sp. nov. (square). B. A. bicolor sp. nov. (circle), A. championi (Jeannel) comb. nov. (triangle) and A. complexus sp. nov. (square). C. A. cona sp. nov. (circle), A. crassicornis sp. nov. (triangle) and A. criniger sp. nov. (square).

FIGURE 93. Environment of and collecting sites at Zhêntang Valley (ĿƋ沟). Slopes at altitudes of 3700 m (A), 4000 m (B), and 3050 m (C). D. Nadang Village (Ḅ当村). E. Road to Xiuxiongma Village (šŏ玛村). F, G. Environment of Ganma Zangbo Valley (HḼẪ布河ě). Photo Credit: F, G by Zhong Peng.