﻿Five new species of Bryaxis Kugelann (Coleoptera, Staphylinidae, Pselaphinae) from Korea and a nomenclatural note on Bryaxismahunkai Löbl

﻿Abstract The genus Bryaxis Kugelann (Goniaceritae: Bythinini) is the most species-rich genus of the subfamily Pselaphinae and is mainly distributed in the Palearctic region. Although previous studies have documented 14 species in the Korean Peninsula, the true diversity, ecology, and immature stages of the genus are still inadequately known. In this study, five new Korean species are described: B.grandinodussp. nov., B.uljinensissp. nov., B.fabaiformissp. nov., B.girinensissp. nov., and B.nemorosussp. nov. Illustrations of the habitus and other morphological details, and a distribution map are provided. In addition, Bryaxisleechanyoungi Nomura & Lee, 1993 is proposed as a new synonym of B.mahunkai Löbl, 1975 based on the original description and illustrations of diagnostic characters.


Introduction
The genus Bryaxis Kugelann, 1794 is the most species-rich pselaphine genus, containing 385 species and 40 subspecies.Except for one adventive species recorded from North America (Chandler 2022) most species of the genus are distributed in the Palearctic and Oriental regions (Newton 2022;Yin 2023).In Northeast Asia,36,10,18,and 19 species are recorded in Japan, the Russian Far East, China, and Taiwan, respectively (Schülke and Smetana 2015;Taru and Nomura 2021;Yin 2023).In Korea, Bryaxis comprises 14 species, 11 of which are endemic (Schülke and Smetana 2015;Ahn et al. 2017).Löbl (1974) first recorded this genus in Korea by describing two species, B. pawlowskii Löbl andB. validicornides Löbl. Nomura andLee (1992, 1993) revised the Korean Bryaxis and described eight species, one of which was later synonymized (B.coreanus Nomura & Lee, 1992 with B. koltzei (Reitter, 1887); Nomura 1995).Members of Korean Bryaxis can be identified by the swollen antennal scape or pedicel with glandular nodule in males (Nomura and Lee 1992).All type specimens were collected from forest leaf litter.Herein we describe five new species by providing illustrations of the habitus and diagnostic characters of each species and a distribution map.Moreover, we found a taxonomic problem regarding Bryaxis leechanyoungi Nomura & Lee, 1993, which is synonymized with B. mahunkai Löbl, 1975 in the present study.

Material and method
Eighty-seven specimens from Chungbuk National University Insect Collection (CBNUIC, Cheongju, Republic of Korea) and one specimen from Chungnam National University Insect Collection (CNUIC, Daejeon, Republic of Korea) were examined.The holotypes of all species described herein are deposited in the National Institute of Biological Resources (NIBR, Incheon, Republic of Korea).Depositions of paratypes and vouchers are indicated parenthetically.At least one specimen of each species was dissected to study the male genitalia and details of other characters.Terminology and nomenclature used follow Chandler (2001)   Diagnosis.Antennal scapes robust, with bowl-like glandular nodule on inner margin (Figs 1E, F, 2A, arrows), 2.45 times as long as pedicels; endophallus of male genitalia with three bifid struts, joined at base (Fig. 1I).

Subfamily
Description.Body reddish brown, antennae, maxillary palpi, and tarsi slightly lighter, length 1.2-1.32mm, maximum width 0.51-0.58mm (Fig. 1A-D).Setae on body yellowish, long.Head 0.92 times as long as wide (Fig. 1E).Frons with U-shaped impression between antennal tubercles; frontal foveae absent; frontal rostrum distinct anteriorly.Vertex slightly convex; longitudinal carina weak; vertexal foveae large.Eyes as long as tempora, with 23-26 facets.Maxillary palpi moderately developed; palpomeres II-III with tubercles; palpomere IV 0.23 mm long and about 3.15 times as long as wide, subcylindrical pseudosegment at apex.Antennae about 0.54 mm long; pedicels subglobose with long setae, 0.89 times as long as wide; antennomere III 1.12 times as long as wide; IV-VIII subequal in length; IX-X transverse, IX 0.64 times as long as wide and X 0.63 times as long as wide; XI largest, pointed at apex, 1.67 times as long as wide (Fig. 1F).Pronotum 0.84 times as long as wide and widest at basal 2/3, lateral antebasal foveae connected by antebasal sulcus.Elytra slightly convex, 0.89 times as long as wide and widest at basal 1/4, each elytron with two basal foveae and subhumeral fovea.Legs slender; protibiae without spine (Figs 1G, 2C); metatibiae with spine at apex (Fig. 1H, arrow).Aedeagus large, 0.37 mm long and 1.69 times as long as wide; penis bulbous and dorsal diaphragm ovoid; parameres short and symmetrical, apices almost encountered, one robust seta and three fine setae on each apex; endophallus divided into three large struts, left dorsal strut branched at basal 1/3 and bifid at apex, right dorsal strut weakly branched basally and bifid dorso-ventrally at apex, ventral strut robust and bifid at apex (Fig. 1I).
Remarks.Adults of this species are very similar to Bryaxis koltzei (Reitter, 1887) in the general body characters, but can be distinguished by the shape of the antennal scapes and its glandular nodule (Fig. 2A, arrow) and the spineless protibiae in the male (Fig. 2C).
Comments.The localities of B. grandinodus sp.nov.probably overlap with those of B. koltzei (Reitter) given that the latter are distributed across the entire country (Fig. 11).
Etymology.The specific epithet is a combination of the Latin words grandis ("large", masculine) and nodus ("knob", masculine) and refers to the shape of the glandular nodules on the male antennal scapes.
Habitat.The holotype was collected by sifting leaf litter in mixed forest.Paratypes were collected by sifting leaf litter and soil.
Etymology.This species is named after the type locality, Uljin-gun.
Habitat.The holotype was collected by sifting leaf litter in mixed forest.Paratypes were collected by sifting leaf litter, soil, and an ant colony.
Remarks.Adults of this species are similar to those of Bryaxis kimjongkuki Nomura & Lee, 1993 in having the maxillary palpomere II-III with tubercles and asymmetrical antennal scapes.However, they can be recognized by having a rounded tempora as long as the eyes (Fig. 6E), a glandular nodule situated at the mid-level of the antennal pedicels (Fig. 6A, arrow), and protibiae without a spine (Fig. 6C).
Comments.The localities of B. fabaiformis sp.nov.probably overlap with those of B. kimjongkuki Nomura & Lee given that the latter species was abundantly collected near the type localities of the former (Fig. 11).
Etymology.The specific epithet is a combination of the Latin words faba ("bean", feminine) and -formis ("having the form of", masculine/feminine) and refers to the shape of antennal pedicels in the male.
Habitat.Specimens of this species were collected by sifting soil and leaf litter in mixed forest.

Bryaxis girinensis
Description.Body reddish brown, antennae, maxillary palpi, and tarsi slightly lighter, length 1.62 mm, maximum width 0.70 mm (Fig. 7A, B).Setae on body yellowish, long and dense.Head long as wide (Fig. 7C).Frons with U-shaped impression between antennal tubercles; frontal foveae absent; frontal rostrum distinct anteriorly.Vertex slightly convex; longitudinal carina present; vertexal foveae small.Eyes large with 34 facets.Maxillary palpi moderately developed; palpomeres II-III with dense tubercles; palpomere IV 0.25 mm long and about 3.30 times as long as wide, subcylindrical pseudosegment at apex.Antennae about 0.54 mm long; scapes subcylindrical, without modification, 1.83 times as long as pedicels; pedicels long as wide; antennomere III 1.70 times as long as wide; IV-VIII subequal in length; IX 0.89 times as long as wide; X 0.78 times as long as wide; XI largest, pointed at apex, 1.86 times as long as wide (Fig. 7D).Pronotum 0.79 times as long as wide and widest at basal 3/5, lateral antebasal foveae connected by antebasal sulcus.Elytra slightly convex, 0.98 times as long as wide and widest at basal 1/3, each elytron with two basal foveae and subhumeral fovea.Legs robust; metatibiae with spine at apex (Fig. 7E, arrow).Aedeagus large, 0.36 mm long and 2.05 times as long as wide; penis fusiform and dorsal diaphragm transversely ovoid; parameres short and symmetrical, apices truncated; endophallus composed of two fine struts, asymmetrical (Fig. 7G).
Remarks.The adult of this species is similar to Bryaxis nemorosus Choi, Park, Lee & Park sp.nov. in the shape of antennomeres IV-XI (Figs 7D, 8F).However, it can be distinguished by the robust setae on the body (Fig. 7A), large eyes as long as the tempora (Fig. 9E), a strongly tuberculate maxillary palpomere II (Fig. 9A), protibiae with a spine at the widest point (Fig. 9C, arrow), and a simple endophallus of the male genitalia (Fig. 7G).

Discussion
This study was the first revision of Korean Bryaxis since Nomura and Lee described eight new species in 1992-1993 [note that Bryaxis coreanus Nomura & Lee, 1992 was subsequently synonymized with Bryaxis koltzei (Reitter, 1887) (Nomura 1995)].According to Kurbatov and Löbl (1995), subgenera Arcobythus Jeannel, 1958and Bythiniama Jeannel, 1958 were synonymized with Bryaxis Kugelann due to the absence of informative characters to separate the genus into subgeneric groups.The adult males of B. nemorosus sp.nov.possess unadorned antennomeres and small eyes, which are thought to be linked to their shady habitat caused by the dense canopy.The features of this species are shown in cavernicolous species (e.g., elongated scapes and reduced eye sizes (Hlaváč 2006;Bekchiev and Hlaváč 2016).However, it is difficult to say whether it belongs to the same lineage as the other cavernicolous species, considering the isolated locality of B. nemorosus sp.nov.
This study added five new species based on 28 specimens.We were able to recollect only three of the species previously described.Of these, B. koltzei (Reitter) and B. mahunkai Löbl were very abundant over their ranges with hundreds of specimens collected.Bryaxis koltzei is a very widespread species present throughout much of eastern Asia, from Korea, north to Russian Far East, and Japan, while B. mahunkai is endemic to Korea.Bryaxis kimjongkuki Nomura & Lee, also endemic to Korea was less abundant than these two, with about 50 specimens collected throughout its range.Two species, B. grandinodus sp.nov.and B. uljinensis sp.nov., were distributed in two localities each (Fig. 11), suggesting the potential for a wide habitat range.
for external characters and Lawrence et al. (2011) for genital characters.Numbering of abdominal sclerites indicate morphological segments.Specimen label data for the holotypes are transcribed verbatim.Data for other specimens are standardized for consistency.Specimens were observed using a Leica M80 and DM1000 LED optical microscope.Images were generated using Sony ILCE-7RM3 mirrorless camera and stacked with Zerene Stacker v. 1.04.The map of Korea was created using the Natural Earth quick start for QGIS v. 3 and open source QGIS v. 3.30.2.For comparison, localities of three dominant species in Korea, Bryaxis mahunkai Löbl, B. koltzei (Reitter) and B. kimjongkuki Nomura & Lee, were also marked.