Arthromelodes crassicornis, 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 : 26-28

Arthromelodes crassicornis sp. nov.

( Figs 9 , 77C , 97C , 100A )

Chinese common name: ÝOnjà甲

Type material ( 59 exx.). HOLOTYPE: CHINA: ♂, ‘China: Xizang, Nyingchi City, Pailong Country , 30°0’34.71”N, 94°57’57.64”E, 2190 m, 2019.vii.17, leaf litter, Z.-W. Yin leg., [ƱẪffżḦË 318 Ǟdzƛḡ]’ ( SNUC). PARATYPES: CHINA: 2 ♂♂, 4 ♀♀, same data as that of holotype; 9 ♂♂, same locality and collector, except vii.15– viii.1, FIT; 13 ♂♂, 12 ♀♀, same locality, except ‘ 2069 m, 30°1’11.1”N, 95°0’0.46”E, 15.viii.2017, X.-B. Song leg.’; 4 ♂♂, 9 ♀♀, same locality, except ‘ 30°0’35”N, 94°57’58”E, 2180 m, 10.vii.2021, Z. Peng, Z. Yin & W. Zhang leg.’; 4 ♂♂, 1 ♀, ‘China: Xizang, Mêdog County, near 80K, 29°41’09”N, 95°30’10”E, alt. 2330 m, mixed leaf litter, sifted, 09.vii.2018, Cheng, Peng & Shen leg.’ (all paratypes in SNUC).

Diagnosis. Male. Body length 1.92–1.94 mm. Head sub-rectangular at base; vertexal foveae large and asetose, lacking sulcus connecting them; antenna short; antennomeres moniliform, 9–11 enlarged and with dense short setae on dorsal surface. Discal stria of elytron extending to apical 2/5 of elytral length. Legs almost simple, only mesotibia with small apical spur. Metaventrite with dense setose area admesally. Sternite 2 (IV) with pair of trichomes lateral to midline. Aedeagus strongly asymmetric; median lobe with large basal capsule and triangular foramen, dilated at apex; dorsal lobe curved, apical part strongly bent downwards, with pointed apex. Female. Body length 1.85–1.92 mm; antennal club and metaventrite lacking modifications, mesotibia lacking apical spur, genitalia as in Fig. 5I .

Description. Male. Body ( Fig. 9A ) length 1.92–1.94 mm; color dark reddish-brown, tarsi and mouthparts lighter. Dorsal surface of body covered with moderately long pubescence.

Head ( Fig. 9B ) sub-rectangular at base, approximately as long as wide, length 0.40–0.43 mm, width across eyes 0.41–0.44 mm; vertex finely punctate, with two exceptionally long setae near base and normal ones, with large, asetose vertexal foveae (dorsal tentorial pits), lacking U-shaped sulcus connecting foveae or mediobasal carina, with T-shaped sulcus at middle and few large punctures anterior and lateral to anterior margin of sulcus; antennal tubercles hardly raised; frons slightly impressed medially, confluent with clypeus; clypeus with smooth surface, its anterior margin carinate and moderately raised; ocular-mandibular carina present. Venter with two small gular foveae (posterior tentorial pits) originating from shared transverse slit, with distinct median carina extending from foveae anteriorly to mouthparts. Eyes moderately prominent, composed of approximately 35 ommatidia. Antenna relatively short, length 0.86 mm, apical three antennomeres forming distinct club; antennomere 1 thick, subcylindrical, 2–8 each moniliform, 9 much larger than 8, 10 slightly longer and broader than 9, 11 largest, as long as 9 and 10 combined, truncate at base and narrowed apically, dorsal surface of antennomeres 9–11 ( Fig. 9C ) covered with short, dense setae.

Pronotum ( Fig. 9B ) approximately as long as broad, length 0.42–0.46 mm, width 0.44 mm, widest at middle; lateral margins rounded; disc slightly convex, finely punctate, with few exceptionally long setae at base and lateral areas of disc and normal ones, median longitudinal sulcus slightly shorter than semicircular lateral sulci in dorsal view, the latter extending from dorsal surface laterally and posteriorly and then fusing with lateral ends of antebasal sulcus; lacking median antebasal fovea, lateral antebasal foveae connected by transverse antebasal sulcus; outer and inner pair of basolateral foveae distinct. Prosternum with anterior part as long as coxal part, with large lateral procoxal foveae; hypomeral ridge present at basal 2/3, with punctiform lateral antebasal hypomeral pit; margin of coxal cavity weakly carinate.

Elytra much wider than long, length 0.57–0.64 mm, width 0.69–0.75 mm; each elytron with two large, asetose basal foveae, lacking subbasal fovea; discal stria extending from outer basal fovea to apical 2/5 of elytral length; humerus weakly prominent, with small subhumeral fovea, sulcate marginal stria extending from fovea to posterior margin of elytron.

Mesoventrite short, demarcated from metaventrite by ridged anterior edges of impressed areas where lateral mesocoxal foveae situated at mesal margins, with pair of thin admesal carinae; setose median mesoventral foveae widely separated, lateral mesoventral foveae large and setose, broadly forked internally; intercoxal process short. Metaventrite ( Fig. 9D ) broadly impressed at middle, lateral areas of impression with long, dense setae; with large, setose lateral mesocoxal foveae and pair of smaller, setose lateral metaventral foveae, posterior margin with small and narrow split at middle.

Legs moderately elongate, lacking distinct modifications. Mesotibia ( Fig. 9E ) with tiny apical tubercle.

Abdomen widest at lateral margins of tergite 1 (IV), length 0.46–0.49 mm, width 0.65–0.67 mm. Tergite 1 (IV) longer than tergites 2–4 (V–VII) combined in dorsal view, setose basal sulcus separated by mediobasal and one pair of basolateral foveae, lacking discal or marginal carinae; tergites 2–4 (V–VII) tightly compressed, each with one pair of basolateral foveae, tergite 4 longer than 2 and 3 combined along middle, tergite 5 (VIII) broad and slightly transverse, posterior margin roundly emarginate at middle. Sternite 2 (IV) with large mediobasal and two pairs of basolateral foveae in broad setose basal impression; midlength of sternite 2 (IV) approximately as long as 3–6 (V–VIII) combined, 3–5 each with one pair of indistinct basolateral foveae. Sternite 7 (IX) ( Fig. 9F ) transverse, posterior margin with scattered setae.

Aedeagus ( Fig. 5G, H ) 0.37 mm long, strongly asymmetric; median lobe with large basal capsule and sub-triangular foramen, ventral stalk in ventral view with broadened apex; dorsal lobe elongate and strongly curved, apically strongly bent downwards and pointed at apex; parameres absent.

Female. Similar to male in external morphology; antenna shorter; antennal club ( Fig. 5I ), metaventrite and sternite 2 (IV) lacking modifications; each compound eye composed of approximately 20 ommatidia; humeral angle rounded; mesotibia lacking apical spur, tergite 5 (VIII) not emarginate medially. Measurements (as for male): body length 1.85–1.92 mm; length/width of head 0.40–0.42/ 0.41 mm, pronotum 0.43/ 0.43–0.44 mm, elytra 0.51– 0.55/ 0.70 mm; abdomen 0.51–0.53/ 0.65–0.68 mm; length of antenna 0.77–0.79 mm; maximum width of genitalia ( Fig. 5J ) 0.25 mm.

Comparative notes. The new species can be readily identified by the unique modifications of the male antennal clubs and the form of the aedeagus. The setose posterior area of the metaventrite of the male is similarly shared with A. nepaeformis and A. lebus , which may indicate close relationships between these species.

Distribution. Chagyib District (Nyingchi) and Mêdog County, Tibet, SW China ( Figs 77C , 97C , 100A ).

Etymology. The specific epithet is formed by the Latin words ‘ crassus -a -um (dense, thick, solid)’ and ‘ cornis (horned)’, referring to the relatively short antennae and stout male antennal clubs of this species.

Figures

FIGURE 5. Morphology of Arthromelodes bicolor sp. nov., male. A. Dorsal habitus. B. Head and pronotum. C. Mesotibia. D. Tergite 1 (IV). E. Sternite 7 (IX). F, G. Aedeagus, lateral (F) and ventral (G). Scale bars: 0.5 mm in A; 0.3 mm in B, D; 0.2 mm in C, F, G; 0.1 mm in E.

FIGURE 9. Morphology of Arthromelodes crassicornis sp. nov. (A–H. Male. I, J. Female). A. Dorsal habitus. B. Head and pronotum. C, I. Antennomeres 9–11. D. Metaventrite and sternite 2 (IV). E. Mesotibia. F. Sternite 7 (IX). G, H. Aedeagus, dorsal (F) and lateral (G). J. Genitalia. Scale bars: 0.5 mm in A; 0.3 mm in B, D; 0.2 mm in C, E, G–J; 0.1 mm in F.

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).

FIGURE 100. Environment of and collecting sites at Nyingchi area (A–E) and Chamdo (ăƀ) (F). A. 80K. B. 96K. C–E. Xiachayu (T察ø). F. pass of Jueba Mountain (ẅ巴山口), Markam (Ẽ康). Photo Credit: A by Zhong Peng; B by Xiao-Bin Song; F by Wen-Xuan Bi.