Arthromelodes flosculus, 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 : 33-34

Arthromelodes flosculus sp. nov.

( Figs 12 , 78A , 99D, G )

Chinese common name: 小ǩnjà甲

Type material ( 1 ex.). HOLOTYPE: CHINA: ♂, ‘ China: Xizang, Mêdog County, nr. Guoguotang Great Ben , 29°18’39.35”N, 95°16’25.75”E, 1180 m, 2019.vii.22, leaf litter, Z.-W. Yin leg., [ƱẪẸṘ果果ḙ]’ ( SNUC).

Diagnosis. Male. Body length over 2.6 mm. Head sub-rectangular at base; vertex with complete reversed Ushaped sulcus connecting vertexal foveae. Head, pronotum, elytra and abdomen with few long thickened, erect setae and normal ones. Legs simple, lacking modifications. Tergite 1 (IV) strongly modified, composed of central cavity filled with specialized trichomes, mediobasal tubercle and lateral setose patches. Aedeagus strongly asymmetric; median lobe with large basal capsule and foramen, dorsal lobe elongate and strongly twisted at apical 1/2.

Description. Male. Body ( Fig. 12A ) length 2.62 mm; color dark reddish-brown, tarsi and mouthparts lighter. Dorsal surface of body covered with long pubescence.

Head ( Fig. 12B ) sub-rectangular at base, approximately as long as wide, length 0.58 mm, width across eyes 0.56 mm; vertex finely punctate, with small, asetose vertexal foveae (dorsal tentorial pits), with complete reversed U-shaped sulcus connecting foveae, mediobasal carina extending from near head base anteriorly to sulcus, with few long thickened setae at antennal tubercles and near base; antennal tubercles slightly raised; frons impressed medially, confluent with clypeus; clypeus with smooth surface, its anterior margin carinate and slightly raised; ocularmandibular carina complete, carina branched below eye, extended ventrally and then anteriorly to posteroventral articulation of mandible. 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 25 large ommatidia. Antenna lacking distinct club and modification, length 1.43 mm; antennomere 1 thick, subcylindrical, 2–11 each elongate, 11 largest, as long as 9 and 10 combined, fusiform.

Pronotum ( Fig. 12B ) slightly broader than long, length 0.60 mm, width 0.56 mm, widest at middle; lateral margins rounded, with few long thickened, erect setae pointed anteriorly; disc slightly convex, finely punctate, with scattered long setae laterally, with one median and one pair of semicircular lateral longitudinal sulci; 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 as long as coxal part, with large lateral procoxal foveae; hypomeral ridge present at basal halves; margin of coxal cavity weakly carinate.

Elytra much wider than long, length 0.82 mm, width 0.98 mm; each elytron with two large, asetose basal foveae; humerus slightly prominent; discal stria extending from outer basal fovea to apical 3/5 of elytral length; subhumeral fovea absent, with carinate marginal stria extending from subbase 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 admesal carinae; setose median mesoventral foveae widely separated, lateral mesoventral foveae large and setose. Metaventrite moderately impressed at middle, with pair of setose lateral metaventral foveae, posterior margin with small and narrow split at middle.

Legs elongate, lacking distinct modifications. Mesotrochanter with small ventral tubercle, mesotibia with tiny tubercle at apex.

Abdomen widest at lateral margins of tergite 1 (IV), length 0.90 mm, width 0.70 mm. Tergite 1 (IV) ( Fig. 12C ) strongly modified, longer than tergites 2–4 (V–VII) combined; structure of modification complex, composed of central cavity filled with specialized trichomes at middle and sides, with large mediobasal tubercle covered with dense setae at apex and broad lateral setose patches with coarse punctation; setose basal sulcus separated by mediobasal and one pair of basolateral foveae, short marginal carinae extending for basal 1/3 of tergal length; 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) 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 small basolateral foveae, sternite 6 (VIII) transverse, posterior margin sinuate, sternite 7 (IX) ( Fig. 12D ) with weakly sclerotized, rounded apex and few long setae along apical margin.

Aedeagus ( Fig. 12E, F ) 0.47 mm long, strongly asymmetric; median lobe with large basal capsule and foramen, basoventral projection short, ventral stalk narrowing apically, with flat apex in ventral view; dorsal lobe elongate and strongly twisted, with pointed apex; parameres reduced and forming single membranous structure.

Female. Unknown.

Comparative notes. The new species can be readily separated from all known congeners by the unique structure of the male modifications on tergite 1 (IV), as well as by the form of the aedeagus. The exceptionally long setae along the posterolateral margins of the head, lateral margins of the pronotum and elytral disc is shared with A. lotus . But otherwise these two species can be readily separated by the larger body size, much more elongate antennae, and a totally different form and structure of the male tergal modification and the aedeagus of A. flosculus .

Distribution. Mêdog County, Tibet, SW China ( Figs 78A , 99D, G ).

Etymology. The specific epithet ‘ flosculus ’ (a small flower, flowery ornament) refers to the flower-like modification of male tergite 1 (IV) of the new species.

Figures

FIGURE 12. Morphology of Arthromelodes flosculus sp. nov., male. A. Dorsal habitus. B. Head and pronotum. C. Tergite 1 (IV). D. Sternite 7 (IX). E, F. Aedeagus, lateral (E) and ventral (F). Scale bars: 0.5 mm in A; 0.3 mm in B, C; 0.1 mm in E; 0.2 mm in E, F.

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 99. Environment of and collecting sites at Nyingchi area. A. Beibeng Township (Ü崩乡). B. Road near Gelin Village (格ff村). C. A bridge at Yarang (亚ü). D. A village near Guoguotang Great Bend (果果Ƌkm弯). E. Environment near Mêdog County (ẸṘ县). F. Path to Renqingbeng Temple (仁ů崩寺). G. An overall view of Guoguotang Great Bend. Photo Credit: E, F by Xiao-Bin Song.