Nebria (Pseudonebriola) tsambagarav sp. nov., a new alpine species from the Mongolian Altai (Coleoptera, Carabidae)

Nebria (Pseudonebriola) tsambagarav sp. nov. is described from an alpine altitude in the Mongolian Altai. The new species is separated from other two Pseudonebriola species from the Mongolian Altai Mountain range, N. kerzhneri and N. medvedevi, by morphometric and morphological analyses. The new species and its habitat are illustrated, the subgeneric key is amended, and a distribution map is given.


Introduction
The subgenus Pseudonebriola Ledoux & Roux, 1989, genus Nebria Latreille, 1802 comprises 13 species and two subspecies (Huber 2017), distributed over the mountain ranges of Central Asia in Kazakhstan, Kirgizia, China, Mongolia, and Russia. The distribution area of Pseudonebriola extends from the Yssyk Kul in Kirgizia to the Baikal Lake in South Eastern Russia. Only the recently described N. (P.) mingyii Ledoux & Roux, 2014 from the Qilian Shan, Qinghai, China, stands isolated from the distribution area of the other species known so far (Ledoux and Roux 2014). Species of the subgenus Pseudonebriola generally inhabit alpine altitudes between 2000 and 3500 m a.s.l.
Up to now four Pseudonebriola species are known from the Altai Mountains, a border mountain range common to Kazakhstan, Russia, China, and Mongolia: N. kaszabi Shilenkov, 1982 from the Kazakhstan and Russian part, N. stanislavi Dudko & Matalin, 2002, an endemic species in the Russian Altai, N. medvedevi Shilenkov, 1982 from the Mongolian (and Russian) Altai, and N. kerzhneri Shilenkov, 1982, endemic to the Gobi Altai, the Southeastern continuation of the Mongolian Altai (Shilenkov 1982a, b;Dudko and Matalin 2002;Ledoux and Roux 2005;Huber 2017).
Pseudonebriola specimens were collected by the junior author on the occasion of an expedition in 2016 to the Tsambagarav uul, Mongolian Altai, Northwestern Mongolia. The Tsambagarav Mountain is part of the central Mongolian Altai bordering the Great Lakes Depression and is separated from the main ridges of the Mongolian Altai by a straight tectonogenic hollow (Borodavko et al. 2018). The collected specimens do not agree either morphologically or morphometrically with any of the known species. Hence they are described below as a new species of the subgenus Pseudonebriola.

Materials and methods
The edeagi and gonocoxae were dissected and dehydrated in alcohol and xylene, and finally embedded in Fluka DPX Mountant on transparent mounting cards.
For a morphometric analysis we measured eleven characters (Table 1) of 31 specimens of four Pseudonebriola taxonomic units from the Altai Mountain range: N. kaszabi (eigth specimens) which belongs to the sajanica species group (sensu Ledoux and Roux 2005), N. medvedevi (two type specimens) and N. kerzhneri (holotype specimen), both of the kerzhneri species group, and a sample of 20 specimens of the type series of the new species from Mt Tsambagarav, Mongolia. The measurements were taken using a Leica MZ 16 stereo-microscope with an ocular micrometer. Measurements of males and females were pooled, since their values were entirely overlapping in range. We applied multivariate ratio analysis (MRA) of Baur and Leuenberger (2011) to our data of a complex of four operational taxonomic units (OTU), the kerzhneri, medvedevi, kaszabi and tsambagarav units. For information on the application of the principal component analysis of shape (shape PCA) and the linear discriminant analysis (LDA) ratio extractor, we refer to the studies on the species complexes of Nebria (Patrobonebria) paropamisos Huber, Schmidt & Baur, 2013(Huber et al. 2013, of N. (P.) desgodinsi Oberthür, 1883 (Huber and Baur 2016), of N. (Eunebria) xanthacra Chaudoir, 1850 (Huber and Schmidt 2018), and of Encarsia pergandiella Howard, 1907 (Hymenoptera, Aphelinidae;Gebiola et al. 2017). Morphometric analyses were done using the R statistical environment (R Core Team 2013).
The photographs were taken with a digital camera Leica MC 190 HD using a motorised focusing drive. The pictures are composites processed using the Leica Application Suite X (LAS X) 3.6.0.20104 software, and were retouched using Adobe Photoshop version 10.0.1. The median lobes of the type specimens of both N. kerzhneri and N. medvedevi were originally glue-fixed on mounting cards. The photographs of the median lobes were taken in that dried situation. The habitus photograph was taken by a digital microscope Keyence VHX-2000 with the objective VH-Z20R.
The distribution map (Fig. 11) was drawn using the QGIS Version 3.8 Zanzibar Software. Additional localities were taken from Shilenkov (1982b;N. medvedevi, N. kerzhneri) and from Dudko and Matalin (2002;N. kaszabi (selection), N. stanislavi, N. medvedevi). In case of non-georeferenced localities we used approximate geo-graphic coordinates of online systems (Google Earth, Google Maps), which are given in square brackets.
Collections examined with acronyms:  Additional localities of non-examined specimens used for the distribution map ( Fig. 11 (Shilenkov 1982b).

Morphometry
The scatterplots of the first scape PC against isosize of the four OTUs do not overlap and show no sign of allometry ( Fig. 1). The kerzhneri red dot, which seems to be close to the tsambagarav scatterplot, lies in a double distance far from the regression line as the furthermost tsambagarav outlier. We consider all units as distinctly separated.
The LDA ratio extractor provides the best ratios to separate the groups. The best two ratios to discriminate the tsambagarav unit from the sample of the two kerzhneri and medvedevi units (ker+med in Fig. 2A) from the Mongolian Altai are the antennal scape length/eye length on the one hand and the elytral width/median pronotum length on the other ( Fig. 2A). We use the former in the determination key below, the second-best ratio is unusual in taxonomy.
Furthermore, we examined eight specimens of N. (P.) kaszabi, a member of the sajanica species group, as a geographical and taxonomic outgroup. The LDA extractor provides the same ratio (the antennal scape length/ eye length) as best ratio to separate the tsambagarav and kaszabi units, supported by the second best ratio of elytral length/head width (Fig. 2B).   Description. Body size: 7.5-9 mm. Colour: Dorsal surface black, head black, without lightened spots on the vertex; appendages of the head brownish lightened, always lighter than the head. Antennal scape black, antennomeres 2-11 brown with darkened apices. Femora black, tibiae and tarsomeres brown, apices of tarsomeres usually black.
Ventral surface: Mes-and Metepisterna smooth and impunctate. Metacoxa basally and apically unisetose. Sternum II laterally faintly and widely dispersed punctate. Sternum III medially asetose. Sterna IV-VI each with one posterior paramedial seta. Anal sternum paralaterally unisetose in the male, bisetose in the female.
Male genitalia: Edeagus (Fig. 7C): Base of the median lobe small; the base decreasing abruptly to the thin midshaft. Mid-shaft strongly curved at base on inner side, moderately curved to the apex. Apex straight, faintly deflected to the left, in front of the long tip ventrally faintly convex. Mid-shaft of the endophallus with short setae.
Habitat (Figs 9, 10). The new species was found in the alpine region of the Tsambagarav uul exclusively un- der bigger stones along the riverbanks of small rivulets. The water ran off higher snowfields. Directly at the snow fields not any specimen was found.
Etymology. The specific epithet refers to the type locality, the Tsambagarav uul; noun in apposition. Distribution (Fig. 11). N. tsambagarav sp. nov. is known only from the type locality at an altitude of 3168 m a.s.l. at the Tsambagarav uul, a mountain (

Differential diagnoses to Pseudonebriola species of the Mongolian Altai
Antennae: Antennal scape (in relation to the eye length) in N. tsambagarav sp. nov. longer than in N. kerzhneri and in N. medvedevi, the ratio scape length/eye length distinctly different: 0.98 in N. tsambagarav sp. nov., 0.89 in N. kerzhneri, and 0.82 in N. medvedevi (see also fig. 2 in Dudko and Matalin (2002), p. 1079).
Pronotum: In N. tsambagarav sp. nov. the lateral groove of the pronotum at the anterior angle is wider than    in N. kerzhneri and N. medvedevi. Lateral margin of the pronotum at the anterior angle distinctly edged as in N. medvedevi; such an edged anterolateral margin is absent in N. kerzhneri. In N. tsambagarav sp. nov. the pronotum is distinctly concave in front of the posterior angles (Fig. 6C), therefore the posterior angle is acute and prominently turned outwards in contrast to the rectangular angle in N. kerzhneri and N. medvedevi respectively, in the latter the pronotal margin in front of the posterior angle is only faintly concave (Fig. 6B).
Edeagus: The tip of the edeagus in N. tsambagarav sp. nov. is longer (Fig. 7C) in contrast to those in N. kerzhneri and N. medvedevi (Fig. 7A, B). Whereas the apex in N. tsambagarav sp. nov. is straight and ventrally faintly convex as in both N. kerzhneri and N. medvedevi, the shortly pointed apex of the edeagus of N. kaszabi is regularly bent without any ventral convexity (Fig. 7D), an indication that N. kaszabi (from Kazakhstan and Russian Altai) may belong to another species group.
Gonocoxa: Gonocoxite 1 of N. tsambagarav sp. nov. (Fig. 8A) wider and gonocoxite 2 less curved than in N. kaszabi (Fig. 8B). Due to scarce material we are not able to evaluate if the observed differences in the gonocoxa habitus are of specific or of species group value.

Discussion
N. tsambagarav sp. nov. is clearly identifiable by its oligosetose 2 nd antennomere. In general the 2 nd anten-nomere of all Pseudonebriola species has a single ventral seta. According to Ledoux and Roux (2005, p. 159) N. stanislavi from the Kazakhstan and Russian Altai also seems to be oligosetose on the 2 nd antennomere ("deuxième article avec deux soies en dessus et une en dessous"), a statement which does not accord with the original description by Dudko and Matalin (2002). There (table p. 1082), the 2 nd antennomere is reported to be unisetose (in 66% of the cases), asymmetrically uni-/bisetose (in 21%) and bilaterally bisetose in 11%; in only 1 single specimen of 47 examined specimens (= 2%) a third seta on the 2 nd antennomere was observed. Therefore, indication in Ledoux and Roux (2005) is incorrect. According to Dudko and Matalin (2002) the 2 nd antennomere in N. stanislavi is exceptionally bi-or trisetose (in 13%), whereas in N. tsambagarav sp. nov. the 2 nd antennomere is exclusively (in 100%) bi-, tri-or even quadrisetose. Additionally the two species differ by the bisetose sterna IV-VI and the antennal scape, which is oligosetose and distinctly longer than the eye length in N. stanislavi, whereas in N. tsambagarav sp. nov. the sterna IV-VI are unisetose, and the antennal scape, which is unisetose, and only as long as the eye length. Within the subgenus Pseudonebriola the oligosetose 2 nd antennomere as a non-incidental peculiarity seems to be limited to N. tsambagarav sp. nov. Ledoux and Roux (2005) divided the subgenus Pseudonebriola into five species groups without specifying any main group characters. The members of the sajanica species group (N. sajanica Bänninger, Figure 11. Map of the Altai Mountain range displaying the distribution of Pseudonebriola species. 1932, N. stanislavi, N. kaszabi) are characterized by the long antennal scape (see figures in Dudko and Matalin (2002) and Ledoux and Roux (2005)). This scape character is vaguely given by Ledoux and Roux (2005) as "long", "very long" or "about two and a half times as long as wide" in N. stanislavi, "quite long" or "two times as long as wide" in N. kaszabi. Effectively this scape slenderness seems to be more pronounced in both species. The measurement of eight specimens of N. kaszabi of the NMBE revealed a ratio scape length/ scape width in N. kaszabi of 2.47±0.06 (2.38-2.52), a value given by Ledoux and Roux (2005) for N. stanislavi. Referring to the figures in Dudko and Matalin (2002; fig. 2, p. 1079) the ratio in N. stanislavi is about 2.8-3.0. Consequently, this deficient description is dissatisfying. It must be an aspect of a general revision of the subgenus Pseudonebriola (which is not the aim of the paper on hand) to clarify and to define characters on which species group arrangement is exactly based. However, the antennal scape in N. tsambagarav sp. nov. is distinctly shorter (ratio scape length/scape width = 2.16) than in N. kaszabi and N. stanislavi of the sajanica species group, but is comparable to those of N. kerzhneri and N. medvedevi (2.16 and 1.91 respectively) of the kerzhneri species group.
The members of the sajanica species group are distributed in the Kazakhstan and Russian part of the Altai Mountain range, in the Sajan Mountains as far as to the Khamar Daban South of Baikal Lake. The members of the sajanica species group of the Kazakhstan and Russian Altai (N. sajanica, N. kaszabi, N. stanislavi) are characterized by the long antennal scape, which is bior oligosetose, and by the tarsomeres with a few dorsal setae. In contrast, the members of the kerzhneri species group (N. kerzhneri, N. medvedevi) are characterized by tarsomeres which are glabrous dorsally, and by the unisetose and short antennal scape. Due to its unisetose and short antennal scape, the dorsally glabrous tarsomeres, and due to the geographic position within the Mongolian Altai the new species N. tsambagarav sp. nov. is assigned to the kerzhneri species group within the subgenus Pseudonebriola.

Key
The determination key of the subgenus Pseudonebriola in Ledoux and Roux (2005) has to be modified in step 8 as follows: