Bryaxis phiaoaci, Mizerakis & Hlaváč & Faille, 2025

Bryaxis phiaoaci sp. nov.

( Figs 1–3 View FIGURE 1 View FIGURE 2 View FIGURE 3 )

Material examined. HOLOTYPE: VIETNAM: ♂, with one white, printed label “Vietnam, Phia Oac NP / 22°36'28''N, 105°52'14''E / 1600 m, 7-8.VI.2024 / sifting in wet forest / P. Hlaváč lgt.“ ( NMPC) / DNA extraction code: VM510 GoogleMaps . PARATYPE: 1 ♂, same data as for holotype ( PCPH) GoogleMaps .

Diagnosis. Body shiny, reddish-brown, appendages slightly lighter; head a little wider than long, coarsely punctate, with large U-shaped impression at frons between antennal tubercles; terminal maxillary palpomere compact and triangular; antennae shorter than the combined length of head and pronotum, with enlarged scape, which is bearing a small glandular tubercle at inner apical third; pronotum 1.3 times as wide as long, widest slightly before anterior third, coarsely punctate and with large lateral antebasal foveae, which are connected by well-defined antebasal sulcus; elytra a little wider than long, with fine punctuation, each elytron with two basal foveae, one subhumeral fovea and entire sutural stria; aedeagus twice as long as wide, parameres basally wide and convergent apically, endophallus with well-defined and symmetrical inner sclerite, slightly exceeding half the length of aedeagus.

Description. Male. Body ( Fig. 2A View FIGURE 2 ) shiny, reddish-brown body; antennae, maxillary palps, and legs slightly lighter. Length about 1.4 mm, maximum width 0.64 mm. Pubescence on body golden, long, sub-erect and relatively sparse.

Head ( Fig. 2B View FIGURE 2 ) subtriangular, about 1.3 times as wide as long, densely and coarsely punctate but shiny; frons between antennal tubercles with deep, wide U-shaped impression, reaching third of length of head capsule, surface shiny; rostrum with straight anterior margin, with very superficial to absent median projection; vertex broad, with fine longitudinal carina, reaching the U-shaped frontal impression; vertexal foveae present, with diameter equal to surrounding punctation; eyes of medium size, with about 25–30 facets.

Maxillary palpi normally developed, with few very superficial ventral tubercles on palpomeres 2 and 3; terminal palpomere (IV) strongly triangular, about 0.8 times as long as head, a little more than twice as long as wide and covered with short, suberect pubescence.

Antennae compact ( Fig. 2C View FIGURE 2 ), shorter than the combined length of head and pronotum; scape enlarged, very wide and modified, 1.3 times longer than wide, a little more than 0.5 times wider than rostrum and widest at the inner apical third, where it is extended triangularly and adorned with a small glandular tubercle; pedicel moderately enlarged, subglobular, slightly longer than wide and slightly arched at inner margin, with width just over half of the width of scape; antennomere 3 longer than wide; antennomeres 4–10 transverse, with 4–6 of equal width and 7–10 gradually widened; antennomere 11 widened and 1.5 times as long as wide; relative length of antennomeres: 1: 0.4: 0.25: 0.19: 0.19: 0.17: 0.17: 0.16: 0.19: 0.24: 0.85.

Pronotum ( Fig. 2B View FIGURE 2 ) densely and coarsely punctate but shiny; 1.3 times as wide as long and 1.3 times as long as head, widest slightly before anterior third; antebasal lateral foveae present, deeply impressed and joined by well-defined antebasal sulcus.

Elytra less shiny than head and pronotum, lacking coarse punctation, only with fine impressions of setal insertion points; 1.15 times wider than long, convex on outer margins; each elytron with two basal foveae, one distinct subhumeral fovea, entire sutural stria.

Legs relatively short, femora slightly swollen, protibiae without preapical indentation on inner margin, meso- and metatibiae simple.

Aedeagus ( Fig. 2D, E View FIGURE 2 ) 0.55 mm long, twice as long as wide; median lobe sub-ovoid; parameres basally wide, moderately convergent to apical third, then abruptly convergent via convex outer margins to pointed apices, with three to four preapical setae; endophallus with well-defined and symmetrical inner sclerites, slightly exceeding half the length of aedeagus; dorsal diaphragm large, occupying 3/4 of aedeagus and oval shaped (appearing converging towards bottom of basal bulb, as osmotic deformation result from the embedding process).

Female. Unknown.

Differential diagnosis. The new species exhibits a close morphological resemblance to the recently described Bryaxis diaoluomontis from Hainan Island, southern China ( Fig. 3 View FIGURE 3 ). Both species share a compact body characterized by relatively short appendages, long suberect pubescence, and dense, very coarse punctation on the head and pronotum, alongside smoother and more superficial punctuation on the elytra. Their antennae are similarly compact, with transverse antennomeres 4–10 and an enlarged male scape that is triangularly extended at the anterior third of the inner margin. Additionally, all tibiae are simple and lack indentation, while the aedeagal endophallus contains symmetrically shaped internal sclerites. However, the new species can be differentiated by several key features: it possesses denser punctation on the head, with inter-punctural distances consistently smaller than the diameter of the punctures (in contrast to B. diaoluomontis , where some inter-punctural distances exceed the puncture diameter). The terminal maxillary palpomere is more triangular in shape, and the pedicel is larger, measuring approximately twice as wide as palpomere 3 (whereas in B. diaoluomontis it is about 1.5 times wider than palpomere 3). Furthermore, the aedeagus of the new species is more slender, being twice as long as it is wide (compared to approximately 1.5 times as long as wide in B. diaoluomontis ), with a significantly thicker basal section of the parameres and a smaller internal sclerites of the endophallus that constitutes just over half the total length of the aedeagus (while in B. diaoluomontis , the internal sclerite approaches the length of the aedeagus itself).

Etymology. Toponymic, named after Phia Oac National Park, type locality in northern Vietnam.

Ecology. The new species was collected by sifting leaf litter in a humid rainforest environment following daily rainfall, at a relatively high altitude of 1600 meters.

Remarks. Phia Oac National Park is home to another species of Bryaxis , although only five female specimens have been collected, preventing a formal description. This species is distinguishable from B. phiaoaci sp. nov. by its larger size and differing punctation patterns on the head and pronotum. Additionally, in the northern region of Vietnam, specifically in Tay Yen Tu Natural Sanctuary, Bac Giang Province, another specimen of Bryaxis sp. was reported by Nomura & Pham (2019). However, the taxonomic relationship between this specimen and the species described herein remains to be further investigated.

Molecular data. The sequence of the partial COI gene of the holotype is deposited in GenBank, under accession number: PQ800730.

Distribution. North Vietnam.