Fifteen new species of Sathytes Westwood from China (Coleoptera, Staphylinidae, Pselaphinae), with an updated checklist of world species

The Chinese fauna of the pselaphine genus Sathytes Westwood (Batrisitae: Batrisini) currently includes 20 species. In this paper, 15 new species from various provinces of the country are described: S. alpicola sp. nov. (Xizang), S. australis sp. nov. (Guangdong, Guangxi), S. chayuensis sp. nov. (Xizang), S. chengzhifeii sp. nov. (Yunnan), S. huapingensis sp. nov. (Guangxi), S. linzhiensis sp. nov. (Xizang), S. maoershanus sp. nov. (Guangxi), S. nujiangensis sp. nov. (Yunnan), S. panzhaohuii sp. nov. (Xizang), S. shennong sp. nov. (Hubei), S. tianquanus sp. nov. (Sichuan), S. transversus sp. nov. (Xizang), S. valentulus sp. nov. (Guangxi), S. xingdoumontis sp. nov. (Hubei) and S. xizangensis sp. nov. (Xizang). New collection records are provided for S. longitrabis Yin & Li, 2012, S. tangliangi Yin & Li, 2012 and S. yunnanicus Yin & Li, 2012. Maps showing the distribution of the genus in China, and an updated checklist of the world species are provided.


Introduction
The ant-loving beetle genus Sathytes Westwood, 1870 of the tribe Batrisini Reitter, 1882 currently comprises 42 described species distributed in the southern Palaearctic and Oriental regions . Members of this group are highly recognizable by their coarse cuticle, while species identifi cations within the genus heavily rely on careful examination of the form of the male antennal clubs, and distributions. The aedeagus, which is normally of great diagnostic signifi cance in beetles, is greatly simplifi ed in Sathytes to form a fl attened, plate-like median lobe, thus is less useful in species identifi cation. The biology of Sathytes is largely unknown. According to existing records, most species were collected from sifted leaf litter samples, such that they are presumed to be predators of smaller invertebrates.
Since the fi rst revision of Sathytes , the known world fauna has increased from 18 species (with an addition of three unnamed species from Pahang, Java and Taiwan) to 42, with 20 additional species described from China (Yin et al. 2012; Shen & Yin 2020), and four species from East Malaysia . Like many other pselaphine groups, the diversity of Sathytes in Asia remains underexplored, especially in those areas where no proper sampling has been pursued. A great number of undescribed species are expected to be found after future fi eldwork has been conducted in these areas.
In the present paper, 15 new species of Sathytes are described from various provinces of China, with their morphology compared to related congeners. Additionally, new collection records are given for three previously known species. The habitus and major diagnostic characters of each new species are illustrated; maps showing the distribution of the genus in China as well as an updated checklist of the world species is provided.

Material and methods
The material treated in this study is housed in the Institute of Zoology, Chinese Academy of Sciences (IZCAS), and the Insect Collection of Shanghai Normal University (SNUC). The label data of the material are quoted verbatim, except for a few modifcations in format required by the journal.
Dissected parts were preserved in Euparal on plastic slides that were placed on the same pin as the specimens. The habitus images were taken using a Canon 5D Mark III camera in conjunction with a Canon MP-E 65 mm f/2.8 1-5 × Macro Lens, and a Canon MT-24EX Macro Twin Lite Flash was used as the light source. Images of morphological details were produced using a Canon G9 camera mounted to an Olympus CX31 microscope under transmitted light. Zerene Stacker (ver. 1.04) was used for image stacking. All images were optimized and grouped into plates using Adobe Photoshop CS5 Extended.

Abbreviations used in measurements
AeL = length of the aedeagus AL = length of the abdomen along midline AnL = length of the antennae AW = maximum width of the abdomen EL = length of the elytra along the suture EW = maximum width of the elytra HL = length from anterior margin of the clypeus to head base, excluding occipital constriction HW = width across the eyes LE = length of the eyes LT = length of the tempora PL = length of pronotum along the midline PW = maximum width of the pronotum TBL = total body length (HL + PL + EL + AL)

Diff erential diagnosis
The male of S. australis sp. nov. shares with S. similis Shen & Yin, 2020 (China: Zhejiang, Jiangxi) the similar body size and structure of the antennal clubs. These two species can be separated only by the following subtle diff erences: in S. australis sp. nov., the eyes are slightly larger, the dorsal margin of antennomere 11 is more convex, the upper (subbasal) protuberance of antennomere 11 is smaller, antennomere 9 in full view (when full widths are visible) is slightly more transverse and the apex of the aedeagus is narrower, and by their diff erent distributions.

Etymology
The specifi c name indicates the distribution of the new species in southern China.    Fig. 2B) about 1.8 times as long as wide, each with two basal protuberances, more apical one short, rounded at apex, more basal one covered with two tufts of setae at apex (Fig. 2D). Pronotum about as long as wide. Elytra strongly transverse. Abdomen widest at tergite 1 (IV) and narrowing apically. Aedeagus (Fig. 2E) slightly asymmetrical at apex.

Female
Unknown.

Diff erential diagnosis
The male of S. chayuensis sp. nov. can be separated from that of all congeners by a single basal protuberance on the terminal antennomere and by the remarkably elongate antennomere 11.

Etymology
The new species is named after Chayu County, where the type locality of this species is situated.

Diff erential diagnosis
The male of S. chengzhifeii sp. nov. is most similar to that of S. huapingensis sp. nov. from Guangxi, China and S. larifuga Shen & Yin, 2019 from Sabah, Borneo, with which it shares the unique, subtriangular basal protuberance of antennomere 11. The new species can be separated from the former by the larger body size (2.69-2.81 mm vs 2.49 mm) and the more basal and more distal positions of the protuberance and apophysis of antennomeres 11 and 9, respectively; and from the latter by the relatively much smaller eyes in relation to the head, more elongate antennomeres 9 and 11, and more distal position of the apophysis of antennomere 9.

Etymology
The new species is named after Zhi-Fei Cheng, one of the collectors of the new species.  4B) about 1.8 times as long as wide, each with single subtriangular and blunt basal protuberance covered with short tuft of setae at apex (Fig. 4D). Pronotum about as long as wide. Elytra strongly transverse. Abdomen widest at tergite 1 (IV) and narrowing apically. Aedeagus (Fig. 4E) fl attened, slightly elongate, and slightly asymmetrical at apex.

Diff erential diagnosis
The male of S. huapingensis sp. nov. possesses a roundly triangular basal protuberance of antennomere 11, similar to that of S. chengzhifeii sp. nov. (China: Yunnan) and S. larifuga (Borneo: Sabah). Sathytes huapingensis sp. nov. can be separated from S. chengzhifeii sp. nov. by the smaller body size (2.49 mm vs 2.69-2.81 mm), and the more distal and more basal positions of the protuberance and apophysis of antennomeres 11 and 9, respectively; and from S. larifuga by the relatively much smaller eyes in relation to the head, much narrower apical portion of the median lobe of the aedeagus, and a diff erent distribution.

Etymology
The new species is named after Huaping Nature Reserve, where the type locality of this species is situated.

Remarks
This species was originally described based on a single male specimen from Houzhenzi, Qinling (秦岭), and is here recorded from Huoditang in the same mountain range. The habitus and diagnostic characters are shown in Fig. 7.

Diff erential diagnosis
The male of the new species shares with S. larinus Yin & Li, 2012 from Zhejiang and Fujian a similar form of the antennal modifi cation, but can be clearly separated by the slightly more transverse pronotum and much larger body size (2.96-3.07 vs 2.17 mm). presence of a single basal protuberance of antennomere 11, and the markedly transverse antennomere 9 (when widths are fully visible). It can be separated from S. transversus sp. nov. by the much smaller body size (2.17 mm vs 2.61-2.72 mm) and less protuberant mesal margin of antennomere 9; from S. valentulus sp. nov. by the thinner antennomere 11 each with a relatively longer basal protuberance, and more transverse antennomere 9; and from S. usitatus by the more oblique anterior margin of antennomere 9 and the more medial positions of the apophyses on these antennomeres.

Female
Unknown.

Diff erential diagnosis
The male of S. panzhaohuii sp. nov. has antennomere 11 each bearing a wide basal protuberance with two tufts of apical setae, a condition unique within the genus which allows ready identifi cation of the new species.

Etymology
The new specifi c epithet 'shennong' (神农) refers to the mythological Chinese deity, from which the name of Shennongjia Nature Reserve originates.

Remarks
This species was originally described based on a male and a female from Qiqi, Gongshan County. An additional specimen shows it has a wider distribution in Yunnan.

Diff erential diagnosis
The male of S. transversus sp. nov. is most similar to that of S. usitatus from Yunnan in the similar form of the antennomeres 9 and 11, but can be clearly separated form it by the larger body size (2.61-2.72 mm vs 2.23-2.42 mm), more posteriorly located apophysis of antennomere 9 and longer basal protuberance of antennomere 11.

Diff erential diagnosis
The male of S. valentulus sp. nov. can be readily separated from all congeners by the markedly stout antennomere 11 alone, aided by the unique form of antennomere 9, and its distribution in Guangxi.

Female
Unknown.

Diff erential diagnosis
Among the species possessing a single basal protuberance of antennomere 11 and a conspicuously oblique mesal margin of antennomere 9 (see Diff erential diagnosis under S. shennong sp. nov.), the male of S. xingdoumontis sp. nov. can be readily distinguished by the unique position and shape of the apophysis of antennomere 9.

Remarks
This species was originally described based on a single male from Qiqi, Gongshan County. Additional specimens show that it has a wider distribution in Yunnan.

Checklist of world species (updated from Yin et al. 2012)
Genus Sathytes Westwood   (by original designation).