Ancystrocerus spatulatus, a new tmesiphorine species from Tham Sai Yok Noi, western Thailand (Coleoptera: Staphylinidae: Pselaphinae)

Abstract: Ancystrocerus spatulatus sp. nov. (Pselaphinae: Tmesiphorini) is described and illustrated from Tham Sai Yok Noi, representing the first Ancystrocerus species in Thailand.


INTRODUCTION
The Oriental genus Ancystrocerus Raffray, 1893 of the ant-loving beetle tribe Tmesiphorini is represented by 12 species distributed in the Philippines (1), Indonesia (4), Singapore (3), Malaysia (2), China (2), and India (1) (Raffray, 1911(Raffray, , 1912;;Yin et al., 2015;Yin, 2020).Members of this group usually bear elongate maxillary palpi, as well as heavily modified male antennal clubs.The males are easily recognizable by their characteristic modifications of antennomeres 9 and 10 (or the lack of such modification), combined with the structures of the aedeagi and distributions.Other than a single female reported from Kaeng Krachan National Park (Nomura et al., 2010), no species of the genus has been formally described from Thailand.In this paper, Ancystrocerus spatulatus sp.nov.from Tham Sai Yok Noi in Kanchanaburi Province, western Thailand is diagnosed, described, and separated from its congeners.

MATERIAL AND METHODS
The type material of the new species described in this paper is deposited in the Muséum d'histoire naturelle, Geneva, Switzerland (MHNG).The label data of the material is quoted verbatim, and a slash (/) is used to separate different labels.The habitus image was taken using a Canon 5D Mark III camera in conjunction with a Mitutoyo M Plan Apo 7.5x Objective, and two Godox V860III-C TTL Li-Ion flashes were used as the light source.Images of morphological details were produced using a Canon G9 camera mounted to an Olympus CX31 microscope under reflected or transmitted light.Helicon Focus v. 8.2.0 Pro was used for image stacking.All images were modified and grouped into plates using Adobe Photoshop CS5 Extended.Measurements were taken as follows: total body length was measured from the anterior margin of the clypeus to the apex of the abdomen; head length was measured from the anterior margin of the clypeus to the head base, excluding the cervical constriction; head width was measured across the eyes; the length of the pronotum was measured along the midline, the width of the pronotum equals the maximum width; the length of the elytra was measured along the suture; the width of the elytra was measured as the maximum width across both elytra; the length of the abdomen is the length of the dorsally exposed part of the abdomen along its midline, the width is the maximum width.The terminology follows Chandler (2001) and Yin (2022).Abdominal tergites and sternites are numbered in Arabic (starting from the first visible segment) and Roman (reflecting true morphological position) numerals, e.g., tergite 1 (IV), or sternite 1 (III).Paired appendages in the description are treated as singular.
Comparative notes: Within the genus, A. spatulatus sp.nov.has the most greatly modified antennomeres 9 and 10 in the male that each of them bears a markedly long, curved tuft of setae.In addition, the short, subtriangular terminal antennomeres, the spatulate setae of the body segments, and the unique form of the aedeagus readily separates this species from all known congeners.Distribution: Thailand: Kanchanaburi Province.

Biological and collection information:
The single male was collected from an endogean environment near Tham Soi Yok Noi, as indicated by the label data.However, the lack of any specialized morphological trait as well as the large eyes suggest this species is more likely epigean.

Etymology:
The specific epithet spatulātus (-ta, -um) is a Latin adjective, meaning, "spatulate, spatula-like", referring to the spatulate setae that cover the body surface.

TAXONOMY Ancystrocerus spatulatus sp. nov.
margin, broadest and with one long tuft of setae at base, 10 with broad and oblique lateral surface slightly impressed, with markedly long, curved tuft of setae at apicolateral margin, 11 roundly triangular, enlarged, shorter than 9 and 10 combined.Pronotum (Fig.1B) longer than wide, length 0.71 mm, width 0.60 mm, widest at middle; sides roundly expanded at widest point and smoothly convergent anteriorly and