Arthromelodes angulatus, 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 : 13-15

Arthromelodes angulatus sp. nov.

( Figs 3 , 77A , 97C )

Chinese common name: Pṅnjà甲

Type material (13 exx.). HOLOTYPE: CHINA : ♂, ‘ China: Xizang, Nyingchi City, Pailong Country , 30°0’34.71”N, 94°57’57.64”E, 2190 m, 2019.vii.15–viii.01, FIT, Z.-W. Yin leg., [ƱẪffżḦËƖǎ]’ ( SNUC) . PARATYPES: CHINA : 1 ♂, same data as that of holotype ; 1 ♂, 1 ♀, same locality and collector, except ‘vii.17, leaf litter’ ; 4 ♂♂, 3 ♀♀, same locality, except ‘ 30°0’35”N, 94°57’58”E, 2180 m, 10.vii.2021, Z. Peng, Z. Yin & W. Zhang leg. ’; 2 ♂♂, same data as precedent, except collected by ‘FIT’ (all paratypes in SNUC) .

Diagnosis. Male. Body length slightly over 2.5 mm. Head sub-rounded at base; vertex with transverse sulcus between antennal tubercles and long mediobasal carina, vertexal foveae large and asetose; antenna long, antennomeres each elongate, lacking modifications. Discal stria of elytron extending to apical 1/5 of elytral length. Fore and hind legs simple, mesotrochanter with small tubercle on ventral margin, mesotibia with tiny apical spur. Abdomen with large tergite 1 (IV) longer than tergites 2–4 (V–VII) combined; tergite 1 (IV) posterolaterally expanded, area mesal to expansion impressed, with transverse central cavity. Aedeagus strongly asymmetric, ventral stalk strongly protruding apically, apex in dorsal view expanded, dorsal lobe strongly curved at apex, parameres reduced and forming single membranous structure. Female. Body length 2.45 mm; mesotibia lacking apical spur, tergite 1 (IV) lacking modifications, genitalia as in Fig. 1H .

Description. Male. Body ( Fig. 3A ) length 2.52–2.53 mm; color reddish-brown, tarsi and mouthparts lighter. Dorsal surface of body covered with moderately long pubescence.

Head ( Fig. 3B ) sub-rounded at base, slightly broader than long, length 0.50–0.52 mm, width across eyes 0.54 mm; vertex finely punctate, with large, asetose vertexal foveae (dorsal tentorial pits), with curved transverse sulcus between antennal tubercles, mediobasal carina extending from near head base anteriorly to sulcus, antennal tubercles weakly raised; frons broadly and shallowly impressed medially, confluent with clypeus; clypeus with smooth surface, its anterior margin carinate and moderately raised; ocular-mandibular carina fusing with ventral margin of antennal socket. Venter with single small gular fovea (posterior tentorial pit), with distinct median carina extending from fovea anteriorly to mouthparts. Compound eyes prominent, composed of approximately 32 large ommatidia. Antenna lacking distinct club and modification, length 1.17–1.21 mm; antennomere 1 thick, subcylindrical, 2–11 each elongate, 11 largest, as long as 9 and 10 combined, sub-fusiform.

Pronotum ( Fig. 3B ) slightly longer than wide, length 0.53–0.56 mm, width 0.49–0.51 mm, widest at middle; lateral margins rounded; disc slightly convex, finely punctate, with median longitudinal sulcus shorter than semicircular 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 slightly longer than coxal part, with distinct 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 0.72–0.78 mm, width 0.86–0.90 mm; each elytron with two large, 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 absent, marginal stria extending posteriorly from middle 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 moderately 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. 3C ) with setose ventral tubercle thin at base and dilated apically, mesotibia with tiny tubercle at apex.

Abdomen narrower than elytra, widest at basolateral margins of tergite 1 (IV), length 0.64–0.79 mm, width 0.80–0.82 mm. Tergite 1 (IV) ( Fig. 3D ) strongly modified, longer than tergites 2–4 (V–VII) combined; basolateral margin angularly expanded laterally, area mesal to expansion broadly impressed, with broad, transverse median cavity, anterior margin of cavity projecting at middle, densely setose lateral to projection, posterior margin broadly projecting, with X-shaped protrusion at middle; setose basal sulcus separated by mediobasal and one pair of basolateral foveae, with very short triangular 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) with mediobasal and basolateral foveae in broad setose basal impression, with pair of short lateral carinae; midlength of sternite 2 (IV) approximately as long as 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. 3E ) with weakly sclerotized, rounded apex and few long setae along apical margin.

Aedeagus ( Fig. 3F, G ) 0.33 mm long, strongly asymmetric; median lobe with large basal capsule and foramen, basoventral projection short, ventral stalk strongly protruding and dilated at apex in dorsal view; dorsal lobe elongate and strongly curved, narrowing apically; parameres reduced to single membranous structure.

Female. Similar to male in external morphology; antenna shorter; legs and tergite 1 (IV) lacking modifications; each compound eye composed of approximately 22 ommatidia; humeral angle rounded. Measurements (as for male): body length 2.45 mm; length/width of head 0.52–0.53/ 0.52–0.54 mm, pronotum 0.51–0.54/ 0.49 mm, elytra 0.59–0.68/ 0.82–0.90 mm; abdomen 0.70–0.72/ 0.82–0.84 mm; length of antenna 1.08–1.13 mm; maximum width of genitalia ( Fig. 3H ) 0.28 mm.

Comparative notes. This species is most similar to A. aniqiao by sharing a similar structure of the male abdominal modifications and the aedeagus, but can be readily separated from the latter by the distinct lateral angulations of the abdomen and a much longer median lobe of the aedeagus. Arthromelodes lage also has the abdominal modifications at a similar location, but lacks lateral angulations of the abdomen, the protibiae are expanded, and the ventral stalk of the aedeagus is relatively much shorter.

Distribution. Chagyib District (巴Ù区) (Nyingchi), Xizang, SW China ( Figs 77A , 97C ).

Etymology. The specific name ‘ angulatus , - a, - um ’ is a Latin adjective meaning ‘cornered, angular’, referring to the laterally expanded male tergite 1 (IV) of this species.

Figures

FIGURE 1. A. Simplified administrative map of Tibet. Produced by Ministry of Natural Resources of Tibet Autonomous Region, available at: http://zrzyt.xizang.gov.cn (Last accessed 2022-01-01). B. Collecting sites in Tibet, with main areas annotated in boxes.

FIGURE 3. Morphology of Arthromelodes angulatus sp. nov. (A–G. Male. H. Female). A. Dorsal habitus. B. Head and pronotum. C. Mesotrochanter. D. Tergite 1 (IV). E. Sternite 7 (IX). F, G. Aedeagus, lateral (F) and ventral (G). H. Genitalia. Scale bars: 0.5 mm in A; 0.3 mm in B; 0.2 mm in C, D; 0.1 mm in E–H.

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 97. Environment of and collecting sites at Nyingchi area. A. Sign of Yigong Tea Farm (ƌŭē厂). B. Forest near Yigong. C. Forest at Pailong Township (ḦË乡). D. Forest near Tongmai Town (ȃ9W).