Sathytes aequalis, 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 : 114-116

Sathytes aequalis sp. nov.

( Figs 49 , 83A , 95A, B )

Chinese common name: ẈƟḛà甲

Type material (16 exx.). HOLOTYPE: CHINA: ♂ , ‘ China: Xizang, Cona County, Lebu Valley , pass to Mama Vill., 27°50’16”N, 91°45’48”E, 2400–2700 m, 04.vii.2021, Z. Peng, Z. Yin & W. Zhang leg., ƱẪDZḄ县勒布沟 Þ玛乡 ’ ( SNUC) . PARATYPE: CHINA: 2 ♂♂, 13 ♀♀, same data as that of holotype ( SNUC) .

Diagnosis. Male. Body length approximately 2.9 mm; ratio (length/width) of head 1.12, pronotum 1.05, elytra 0.82–0.86, length of eye/tempus 0.82. Antennomere 9 as long as wide (length/width excluding apophysis 1.03), with hyaline apophysis at middle of strongly oblique mesal margin, antennomere 11 elongate (length/width 2.07), with distinct protuberance at base, apex of protuberance with tuft of curved setae. Aedeagus broad throughout length, with slightly emarginate apical margin. Female. Body length approximately 3.0 mm; antenna lacking modifications, genitalia as in Fig. 49G .

Description. Male. Body ( Fig. 49A ) length 2.87–2.95 mm; color reddish-brown, tarsi and mouthparts lighter. Dorsal surface of body covered with short pubescence.

Head ( Fig. 49B ) sub-rectangular at base, slightly longer than wide, length 0.63–0.64 mm, width across eyes 0.56–0.57 mm, length/width 1.12; vertex moderately raised, with small asetose foveae (dorsal tentorial pits) located posterior to level of posterior margin of eyes; frons anteriorly confluent with strongly declining clypeus, shallowly impressed medially; clypeus with smooth surface, anterior margin carinate and moderately raised; ocular-mandibular carina short; postgenal region strongly projecting. Venter with small, broadly separated gular foveae (posterior tentorial pits), lacking distinct median carina or sulcus. Compound eyes prominent, composed of approximately 19 large ommatidia, length of eye/tempus 0.82. Antenna elongate, length 1.49–1.54 mm, distinct club ( Fig. 49C ) formed by enlarged apical three antennomeres; antennomere 1 thick, subcylindrical, 2–7 each transverse, subequal in width, 8 slightly shorter than and as broad as 7, 9 ( Fig. 49D ) strongly enlarged, approximately as long as wide, length/width excluding apophysis 1.03, mesal margin expanded at middle, anterior half strongly oblique, hyaline apophysis located at approximately middle of mesal margin, 10 transverse, length/width 0.71, 11 largest, approximately as long as 9 and 10 combined, length/width 2.07, with distinct protuberance at base, apex of protuberance with curved tuft of golden setae.

Pronotum ( Fig. 49B ) approximately as long as wide, length 0.63–0.68 mm, width 0.60–0.63 mm, length/width 1.05, widest at middle; lateral margins rounded, convergent apically and basally; disc weakly convex; asetose lateral antebasal foveae distinct. Prosternum with anterior part slightly longer than coxal part, with small lateral procoxal foveae; hypomeral ridge absent; margin of coxal cavity moderately carinate.

Elytra much wider than long, length 0.92–0.98 mm, width 1.12–1.14 mm, length/width 0.82–0.86; each elytron with four large, asetose basal foveae; discal stria shallow and short, present only near base; humerus weakly prominent, subhumeral fovea present, marginal stria extending from fovea to posterior margin of elytron.

Mesoventrite short, demarcated from metaventrite by strongly curved carinae; median mesoventral foveae fused, large lateral mesoventral foveae forked internally, mesoventral process short. Metaventrite moderately prominent admesally, weakly inclined towards middle, with well-developed lateral mesocoxal and two lateral metaventral foveae, lacking median pit anterior to posterior margin, posterior margin broadly emarginate at middle, with thin marginal carina.

Legs elongate, simple.

Abdomen widest at lateral margins of tergite 1 (IV), length 0.80–0.85 mm, width 0.99–1.00 mm. Tergite 1 (IV) more than twice as long as 2 (V), lacking basal sulcus, with one pair of mediobasal and two pairs of basolateral foveae, lacking discal and marginal carina; tergite 2 (V) slightly longer than 3 (VI), 4 (VII) longer than 3 but much shorter than 2 and 3 combined; tergites 2–3 (IV–VI) each with one pair of mediobasal and two pairs of basolateral foveae, 4 with one pair of basolateral foveae and marginal tubercles, tergite 5 (VIII) semicircular, transverse, posterior margin roundly emarginate at middle. Sternite 2 (IV) with one pair of mediobasal and three pairs of basolateral foveae, lateral carina absent; midlength of sternites 2–5 (IV–VII) gradually shorter, sternites 3–4 (IV–VI) each with three pairs and 5 (VII) with one pair of small basolateral foveae, sternite 6 (VIII) transverse, posterior margin broadly emarginate, sternite 7 (IX) ( Fig. 49E ) moderately sclerotized, elongate, apex lacking setae.

Aedeagus ( Fig. 49F ) 0.32 mm long, slightly asymmetric, plate-like, with large foramen, median lobe broadened throughout entire length, with apex approximately as wide as base, apical margin slightly emarginate.

Female. Similar to male in external morphology; antenna slightly shorter, lacking modifications; each compound eye composed of approximately 13 ommatidia; humerus faintly prominent; metaventrite with round median pit shortly anterior to posterior margin. Measurements (as for male): body length 2.95–3.13 mm; length/width of head 0.63/ 0.56–0.59 mm, pronotum 0.67–0.70/ 0.62–0.68 mm, elytra 0.85–0.94/ 1.11–1.16 mm; abdomen 0.91– 1.0/ 1.02–1.06 mm; length of antenna 1.34–1.37 mm; maximum width of genitalia ( Fig. 49G ) 0.31 mm.

Comparative notes. The male of this species resembles that of S. chayuensis present in Zayü County (察ø 县) in the similar body size, relatively long antennomere 11, and similar form and structure of antennomere 9. They can be separated by the following subtle differences: 1) the more convergent postocular margins and less rounded posterolateral angles, 2) the setae of the head are much longer and less dense, 3) a relatively more elongate (less rounded) pronotum (relative length/width: 80/71 vs. 80/78), and 4) a different fine structure of the hyaline apophyses of antennomeres 9 and the different form of the aedeagus of S. aequalis (left portion of apical margin of the median lobe distinctly convex in S. chayuensis ). Note these differences can be reliably determined only through direct comparisons between the specimens of the two species, not the figures. Sathytes aequalis is also similar to S. virupaksa in the form of male antennomeres 9, but can be readily separated by the large body size, the longer postocular margins in relation to eye length, the larger basal protuberances of male antennomeres 11, a much more elongate male sternite 7 (IX), and a non-dilated apex of the aedeagus.

Distribution. Cona County, Tibet, SW China ( Figs 83A , 95A, B ).

Etymology. The new species name ‘ aequâlis (similar, resembling in size or form)’ is a Latin adjective suggested by the morphological similarity of the new species to S. chayuensis .

Figures

FIGURE 49. Morphology of Sathytes aequalis sp. nov. (A–F. Male. G. Female). A. Dorsal habitus. B. Head and pronotum. C. Antennomeres 9–11. D. Antennomere 9. E. Sternite 7 (IX). F. Aedeagus, ventral. G. Genitalia. Scale bars: 0.5 mm in A; 0.3 mm in B, C; 0.1 mm in D–G.

FIGURE 83. Distribution of Tibetan Batrisini. A. Sathytes aequalis sp. nov. (circle), S. alpicola Yin & Shen (triangle) and S. asura sp. nov. (square). B. S. caichenyangi sp. nov. (circle), S. chayuensis Yin & Shen (triangle) and S. dawai sp. nov. (square). C. S. duojii sp. nov. (circle), S. laticornis sp. nov. (triangle) and S. linzhiensis Yin & Shen (square).

FIGURE 95. Environment of and collecting sites at Lebu Valley (勒布沟). Forests at 2400 m (A, B), and 3650 m (C, D).