Six new species of Horniella Raffray from the Oriental region (Coleoptera, Staphylinidae, Pselaphinae)

Abstract The Oriental pselaphine genus Horniella Raffray, 1905 currently contains 29 species. In this paper, six new species are described: H. nantouensis Zhang, Hu & Yin, sp. nov. and H. taiwanensis Zhang, Hu & Yin, sp. nov. from Taiwan, China; H. bifurca Zhang & Yin, sp. nov. and H. haucki Zhang & Yin, sp. nov. from Thailand; H. khasiensis Zhang & Yin, sp. nov. from northern India; and H. sabahensis Zhang & Yin, sp. nov. from eastern Malaysia. In addition, H. aculeata Yin & Li, 2015, originally described from Yunnan, China, is newly recorded from Thailand.


Introduction
The Oriental pselaphine genus Horniella Raffray, 1905 (Tyrini: Somatipionina) currently includes 29 species distributed in China (12 spp.), Thailand (9 spp.), Malaysia (4 spp.), Nepal and India (1 sp.), Sri Lanka (1 sp.), the Philippines (1 sp.), and Indonesia (1 sp.) (Raffray 1905;Li 2014, 2015;Newton 2020). Members of this genus are easily recognizable by their medium-sized to large body, enlarged maxillary palpomeres 4 that lack an apical palpal cone, presence of a frontal fovea on the head, weakly to greatly developed anterolateral genal projections, pronotum with median and lateral antebasal foveae that are connected by an antebasal sulcus, and usually medially carinate abdominal tergite 1 (IV) that is longer than tergite 2 (V). The known species were placed in four groups (Yin and Li 2014), which are followed here. The H. centralis group, with nine species, is defined by the distinct apicolateral genal projections, the head with a pair of long, curved ocular canthi, and the apical portion of the aedeagal median lobe with the right or left half strongly projecting apically. The H. burckhardti group, also containing nine species, is morphologically similar to the H. centralis group, but the apical portion of the aedeagal median lobe narrows apically. The H. hirtella group, represented by six species, lacks distinct apicolateral genal projections and ocular canthi, and the aedeagus usually has a relatively simple endophallus (membranous structures containing many small denticles). The H. gigas group, including three species, lacks obvious apicolateral genal projections or ocular canthi, each of the apical three antennomeres is distinctly elongate, maxillary palpomeres 2 are conspicuously elongate, tarsomeres 2 extend to near the midlength of tarsomeres 3, and the endophallus of the aedeagus has simple sclerites and/or small denticles on a membranous structure. A large number of unassociated females have been listed by Li (2014, 2015), which indicates that the true diversity of this group still remains underexplored.
Based on an examination of additional material deposited in the Muséum d'Histoire Naturelle, Geneva, Switzerland, and the National Museum of Natural Science, Taichung City, Taiwan, China, we describe here six new species from China (2), Thailand (2), India (1), and Malaysia (1). Thus, the total species number of Horniella raises from 29 to 35. Furthermore, new collecting data of Horniella aculeata Yin & Li from Thailand are provided.

Material and methods
The type material of the new species described in this paper is deposited in the Muséum d'Histoire Naturelle, Geneva (MHNG), the National Museum of Natural Science, Taichung City, Taiwan (NMNS), and the Insect Collection of Shanghai Normal University, Shanghai (SNUC).
Dissected parts were preserved in Euparal on plastic slides that were placed on the same pin with the specimen. The habitus images of the beetles 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 the morphological details were produced using a Canon G9 camera mounted to an Olympus CX31 microscope under reflected or transmitted light. Zerene Stacker v. 1.04 was used for image stacking. All images were modified and grouped into plates using Adobe Photoshop CC 2020.
The abdominal tergites and sternites are numbered following Chandler (2001) 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 structures in the species descriptions are treated as singular.
The collecting data of the material are quoted verbatim. The Chinese translation of each locality is included in parentheses at first appearance in the text. A slash is used to separate different labels. Each type specimen bears the following label: 'HOLOTYPE [red] (or PARATYPE [yellow]), ♂ (or ♀), Horniella + specific name sp. n., det. Zhang & Yin, 2021, NMNS (or MHNG, or SNUC)'.
The following abbreviations are applied: AL = length of the dorsally exposed part of the abdomen (posterior to elytra) along the midline; AW = maximum width of the abdomen; EL = length of the elytra along the suture; EW = maximum width of the elytra; HL = length of the head from the anterior clypeal margin to the anterior margin of the occipital constriction; HW = width of the head across eyes; PL = length of the pronotum along the midline; PW = maximum width of the pronotum. Length of the body is a sum of HL + PL + EL + AL.
Remarks. Horniella aculeata is readily recognizable by the presence of a large spine on the mesal margin of the protibiae (Yin and Li 2015: fig. 2F), and the aedeagus with one elongate, twisted sclerite (Yin and Li 2015: fig. 2K). This species was described based on two male and four female specimens from Yunnan, China, and the present record extends its distribution to Thailand.

Horniella bifurca
Diagnosis. Male. Head approximately as long as wide, with distinct anterolateral genal projection, anterior margin of projection roundly emarginate; with long, apically forked ocular canthus; scape angularly expanded at anterolateral margin, antennomeres 9-11 moderately enlarged. Pronotum rounded at anterolateral margins. Protrochanter and profemur each with long ventral spine; protibia with small triangular apical spur; mesotrochanter with short but distinct ventral spine. Tergite 1 (IV) with median carina extending posteriorly for approximately 1/4 of tergal length, discal carinae long and thick. Aedeagus with asymmetric median lobe, right half of median lobe greatly protruding apicad, left half strongly curved and forked at apex; endophallus composed of two elongate, twisted sclerites.
Female. Similar to male in external morphology, profemur each with two ventral spines near base, protibia lacking preapical spur, mesotrochanter lacking ventral spine; genital complex as in Fig. 10A.
Pronotum as long as wide, PL and PW 0.67 mm, widest at apical 1/3; anterolateral margins rounded; disc moderately convex, finely punctate, with distinct median antebasal and lateral antebasal foveae connected by complete transverse sulcus.
Comparative notes. This species is placed as a member of the H. centralis group. It can be readily separated from the other members of the group by the long, apicallyforked ocular canthi, as well as by the unique shape of the aedeagus.
Distribution. Thailand: Chiang Mai. Etymology. The new specific epithet bifurca (-us, -um) is a Latin adjective means 'two-pronged', referring to the apically-forked ocular canthus of the new species.  Diagnosis. Male. Head longer than wide, with distinct anterolateral genal projection, anterior margin of projection roundly emarginate; with long ocular canthus; scape angularly expanded at basolateral margin, antennomeres 9-11 moderately enlarged. Pronotum rounded at anterolateral margins. Protrochanter and profemur each with long ventral spine; protibia strongly curved near apex, with long apical projection; mesotrochanter with large sharp ventral spine, mesofemur distinctly arched. Tergite 1 (IV) with median carina extending posteriorly for approximately 3/4 of tergal length, discal carinae short and thin. Aedeagus with asymmetric median lobe, left half of median lobe greatly protruding in dorso-ventral view; endophallus composed of three long sclerites.
Pronotum as long as wide, PL and PW 0.64 mm, widest anterior to middle; lateral margins rounded; disc moderately convex, finely punctate, with distinct median antebasal and lateral antebasal foveae connected by complete transverse antebasal sulcus.
Elytra much wider than long, EL 0.75 mm, EW 1.2 mm; each elytron with two large, setose basal foveae; discal striae extending from outer basal foveae to near posterior margin of elytra.
Aedeagus (Fig. 5G-I) 0.59 mm long, median lobe nearly symmetric, apex broadly truncate; endophallus composed of three sclerites: one elongate, plate-like sclerite with curved lobe at apex; one curved sclerite at base, and one much narrower sclerite at left.
Female. Unknown.  Comparative notes. This species is placed as a member of the H. burckhardti group, and is most similar to H. hongkongensis Yin & Li in having similar spination of the legs and a general aedeagal form. They can be clearly separated by the more distinctly expanded basolateral margin of the scape, tergite VIII with a large medioapical process, and the different structure of the aedeagal endophallus.
Distribution. India: Meghalaya. Etymology. The new species is named after its type locality, the East Khasi Hills. Diagnosis. Male. Head longer than wide, with weakly indicated anterolateral genal projection, anterior margin of projection oblique; with short ocular canthus; lateral margin of scape straight, antennomeres 9-11 slightly enlarged. Pronotum rounded at anterolateral margins. Ventral margin of profemur with one short and acute, and one tiny spine at base; protibia with one small preapical denticle. Tergite 1 (IV) with median carina extending posteriorly for approximately 1/3 of tergal length, lacking discal carinae. Aedeagus with asymmetric median lobe, apical part of median lobe narrowed and protruding apicad, apex nearly rounded in dorsal view. Female. Similar to male in external morphology, profemur with two ventral spines near base; genital complex as in Fig. 10B.
Elytra much wider than long, EL 0.85 mm, EW 1.33 mm; each elytron with two large, setose basal foveae; discal striae extending from outer basal foveae to middle of elytral length.
Aedeagus (Fig. 6G-I) 0.57 mm long, with asymmetric median lobe, apical portion of median lobe narrowed and greatly protruding apically, apex nearly rounded in dorsal view; endophallus composed of broad membranous part with single broad elongate sclerite at middle.
Comparative notes. This species is placed as a member of the H. hirtella group. The new species is similar to H. simplaria Yin & Li by the male having similar anterolateral genal projections, and presence of two ventral spines of profemur. They can be otherwise clearly separated by the larger body size (3.68 mm vs 3.23 mm), lack of a mesal hook-like spine of the protibia (present in H. simplaria), and the different shape and structure of the aedeagus of the new species.
Distribution. China: Taiwan. Etymology. The new specific is named after its type locality, Nantou County. Diagnosis. Male. Head longer than wide, anterolateral genal projections weakly developed, anterior margin of projection oblique; scape lacking expansion at lateral margin, antennomeres 9-11 moderately enlarged, forming distinct club. Pronotum rounded at lateral margins. Profemur with two tiny ventral spines near base; metatibia with preapical triangular denticle. Tergite 1 (IV) with median carina extending posteriorly for approximately 3/4 of tergal length, lacking discal carinae, tergite 2 (V) with short median carina. Aedeagus with slightly asymmetric median lobe, apical portion of median lobe narrowed, apex truncate in dorso-ventral view; endophallus lacking sclerite, composed of elongate membranous structure with many small denticles.
Pronotum distinctly longer than wide, PL 0.71 mm, PW 0.6 mm; widest at middle; lateral margins rounded; disc moderately convex, finely punctate, with distinct median antebasal and lateral antebasal foveae connected by complete transverse antebasal sulcus.
Female. Unknown. Comparative notes. Horniella sabahensis sp. nov. is placed as a member of the H. hirtella group. Males of this species share with H. prolixo Yin & Li from Thailand the weakly developed anterolateral genal projections, lack of an expansion at the lateral margin of the scape, and a moderately expanded preapical portion of the metatibia. They can be best separated by the larger body size (3.41 mm vs 2.95-3.02 mm), tergite V with a short median carina (lacking in H. prolixo), as well as the much narrower apex of the aedeagus of the new species.
Distribution. East Malaysia: Sabah. Etymology. The new species is named after its type locality, Sabah, East Malaysia. Diagnosis. Male. Head longer than wide, with distinct anterolateral genal projections, anterior margin of projection narrowly emarginate, with long ocular canthus; scape roundly expanded at basolateral margin, antennomeres 9-11 slightly enlarged. Pronotum rounded at anterolateral margins. Protrochanter, profemur and mesotrochanter each with ventral spine; protibia and mesotibia with large apical projection. Tergite 1 (IV) with median carina extending posteriorly for approximately 1/4 of tergal length, lacking discal carinae. Aedeagus with asymmetric median lobe, right half of median lobe greatly protruding apicad, apical margin nearly rounded in dorsal view.
Female. Unknown. Comparative notes. This species is placed as a member of the H. centralis group and is most similar to H. sichuanica Yin & Li in the shapes of the anterolateral genal projections and spination of the legs. They can be clearly separated by the larger body size (4.05-4.15 mm vs 3.58-3.77 mm), the more distinct apical projections of protibia and mesotibia, and the dilated apex of the aedeagal median lobe of the new species.
Distribution. China: Taiwan. Etymology. The new specific is named after Taiwan.