Disarthricerus dulcissimus Yin, Nomura, Hlaváč & Lü, 2025

Yin, Zi-Wei, Nomura, Shûhei, Hlaváč, Peter & Lü, Liang, 2025, Disarthricerus dulcissimus sp. nov. (Coleoptera, Staphylinidae, Pselaphinae): a precious dwarf from the north, Deutsche Entomologische Zeitschrift 72 (2), pp. 517-524 : 517-524

Disarthricerus dulcissimus Yin, Nomura, Hlaváč & Lü sp. nov.

Figs 1 , 3 Chinese common name: 奇珍羔蚁甲

Type material.

Holotype: China: • ♂, ‘ China: Yunnan, Xishuangbanna, Mengla County, Menglun Town, Mangang Mt. , 21.951368°N, 101.258613°E, alt. 640 m, 8–10.v.2025, FIT, L. Lü leg., 云南勐腊勐仑曼冈山飞阻吕亮采’ ( SNUC) . Paratype: China: • 1 ♂, also from Menglun, same collector and method, except ‘ Namiao River (那苗河), 21.929558°N, 101.192047°E, alt. 710 m, 13–16.v.2025 ’ ( SNUC) .

Diagnosis.

Male. Habitus rather stout, with short antennae and legs. Body length approximately 1.1 mm. Eyes small (compared to congeners), broadly separated; antenna with two observable antennomeres; terminal antennomere nearly straight, dorsally exposed part approximately 3.6 × as long as wide. Pronotum with sparse, distinct punctures. Elytra reticulate at center of disc. Legs simple, lacking modifications. Composite tergite (IV – VI) of abdomen laterally with pair of oblique, longitudinal cavities. Sternite 2 (IV) with complete lateral carinae. Aedeagus elongate, dorsoventrally symmetric; apex of median lobe narrowed, curved ventrally; parameres dorsally fused with median lobe, elongate and slender, with rounded, asetose apices. Female. Unknown.

Description.

Male. Body (Fig. 1 A ) stout; length 1.08–1.12 mm; colour reddish brown, with paler tarsi and mouthparts. Dorsal vestiture consists of sparse, suberect golden setae.

Head capsule (Fig. 1 B ) dorsally subcylindrical, significantly longer than wide, length 0.30 mm, width across eyes 0.21 mm; vertex depressed at level of posterior margin of eyes, with coarse surface, lacking foveae (dorsal tentorial pits); frons with sparse, large punctures, evenly elevates to form broad rostrum, which then descends sharply and features vertical, anteriorly divergent keel at middle; clypeus markedly short, small, with sparse setae on its anterior margin. Venter with reticulate surface; gular region broadly, moderately impressed, with single small pit containing tiny foveae (posterior tentorial pits); lacking median longitudinal carina. Compound eyes moderately prominent, each having approximately 32 ommatidia. Head capsule slightly expanded posteriorly, not separated from ‘ neck’ region, surface of cervical part with reticulate microsculpture especially distinct at middle. Antenna (Fig. 1 C ) 0.32 mm long, with two observable antennomeres and lacking modifications; antennomere 1 short, transverse, dorsally invisible as completely hidden beneath rostrum; terminal antennomere elongate, with dorsally visible part approximately 3.6 × as long as wide, broadened slightly toward rounded apex; few indistinct sutures at basal portion suggest fusion of apical antennomeres.

Pronotum (Fig. 1 B ) pentagonal, wider than long, length 0.23–0.24 mm, width 0.31–0.32 mm, widest at its posterior angles; anterior margin broadly, slightly impressed medially; lateral margins nearly straight, divergent posteriorly; posterior margin convex, obtusely angled at middle; disc weakly impressed mediobasally, with sparse, large punctures, lacking foveae. Prosternum with basisternal (precoxal) portion much longer than procoxal rests; with tiny, well-separated procoxal foveae. Hypomera largely fused with prosternum, lacking hypomeral grooves; hypomeral carinae weakly prominent, clinging to lateral edges of coxal cavities.

Elytra together broadly transverse, sub-rectangular, length 0.36–0.37 mm, width 0.54 mm; anterior margins distinctly inclined medially; lacking basal foveae, carinae, or sulci, but with well-marked reticulate sculpture at center; humeri broadly rounded, flat, with thin marginal carinae extending from humeral bases to beyond half elytra length; posterolateral margins broadly rounded; with nearly straight posterior margins. Metathoracic wings fully developed.

Mesoventrite short, laterally fully demarcated from metaventrite by oblique carinae; median mesoventral foveae narrowly separated, located anterior to median keel; with pair of small lateral mesoventral foveae and short lateral longitudinal carinae. Metaventrite roundly, broadly convex at middle, descending laterally, with distinct reticulate sculpture on lateral portions; small lateral metaventral foveae present; metaventral intercoxal process broadly separating coxae, weakly convex medially.

Legs short, lacking modifications; tibiae broadened in their apical halves.

Abdomen sub-semicircular, distinctly narrower than elytra, length 0.22–0.24 mm, width 0.45 mm, widest at basolateral margins of composite tergite. Composite tergite (IV – VI) convex medially, with oblique lateral carinae extending from tergal base posterolaterally to approximately 2 / 5 of tergal length, forming lateral edges of longitudinal cavities; each cavity with basolateral fovea at its anterior end and lateral fovea at its posterior end; tergite 2 (VII) short, greatly transverse, with pair of small basolateral foveae; 3 (VIII) subtrapezoidal, transverse, with small basolateral foveae and broadly concave posterior margin. Sternite 2 (IV) broadly, moderately convex medially; with thin, posteriorly divergent lateral carinae that extend parallel to posterior margin of sternite approximately posterior to basal 1 / 5; 3–5 (V – VII) of subequal length at middle; each short, transverse, lacking foveae; 6 (VIII) transverse, lacking foveae; presumed sternite 7 (IX), or genital plate (Fig. 1 D ), of membranous, sub-annular structure that encircles apical part of aedeagus.

Aedeagus (Fig. 1 E, F ) 0.13 mm long, elongate, dorsoventrally symmetric; median lobe with extensive, basally rounded capsule, transversely oval foramen, and large oval diaphragm; apical 1 / 4 narrowed into ventrally bent apex; endophallus armature composed of many membranous, spine-like structures mostly in central part; parameres dorsally fused with ventral wall of median lobe; each elongate, slender, moderately expanded at its rounded, asetose apex.

Female. Unknown.

Comparative notes.

This species differs from D. bruneicus by its straight terminal antennomeres and unmodified male legs, in contrast to the basolaterally curved antennomeres and large ventral spines on the mesofemora of the latter species. From D. moultoni , it differs in the much longer antennae relative to head length and the simple mesofemora; the latter species possesses antennae that are distinctly shorter than the head capsule and femora bearing one long and one short ventral spine. Compared to the type species, D. integer , the new species has proportionately shorter and more robust terminal antennomeres (antennae much longer than the head and at the bases distinctly narrower than at the apices in D. integer ). Furthermore, the new species has relatively the smallest male eyes among known congeners, which makes them appear quite “ broadly separated. ”

Natural history.

Eight flight intercept traps were deployed in various locations in the mixed evergreen tropical forests surrounding the Xishuangbanna Tropical Botanic Garden. Despite careful stereomicroscopic examination of the material collected over several weeks, this extensive sampling effort yielded only two adult specimens. Such a low recovery rate implies that in mid-May the species either exists at a very low population density or exhibits a high degree of microhabitat specificity, perhaps in association with an as-yet unidentified symbiotic host. A summary of the current knowledge regarding distribution, collecting methods, host associations, and specimen availability for all known Disarthricerus species is presented in Table 1 .

Distribution.

Southwest China: Yunnan (Fig. 3 ).

Etymology.

The epithet is a Latin adjective that means “ sweetest, most charming. ” This name refers to the beetle’s charming and delicate appearance.

Figures

Figure 1. Disarthricerus dulcissimus sp. nov., male. A. Dorsal habitus; B. Head and pronotum; C. Antenna, lateral; D. Presumed sternite 7 (IX); E, F. Aedeagus, lateral (E) and ventral (F). Scale bars: 0.2 mm (A, B); 0.1 mm (C); 0.05 mm (D – F).

Figure 3. Distribution and habitat of Disarthricerus Raffray. A. Distribution of Disarthricerus species, showing significant range extension following the discovery of the new species in China; B. Collecting environment of D. dulcissimus sp. nov. A flight intercept trap deployed in an evergreen broad-leaved forest of Mangang Mountain, Yunnan.