Contribution to the knowledge of the oribatid mite genus Perxylobates (Acari, Oribatida, Haplozetidae)

Perxylobates hakkai n. sp. (Oribatida, Haplozetidae) is the second representative of the genus recorded in Taiwan; it is described based on adults from soil under Ricinus communis on a farm of the Agricultural Research and Extension Station in Miaoli District. The new species differs from related Perxylobates coreanus Choi and Aoki, 1993 by the presence of five pairs of genital setae (versus four pairs), four pairs of notogastral porose areas including A3 (versus three pairs, A3 absent), minute epimeral seta 1c (versus comparatively long), roughened epimeral and aggenital setae (versus heavily barbed), and smooth anterior part of prodorsum (versus foveolate). A revised generic diagnosis and an identification key to known species of Perxylobates are provided. The systematic placement of Perxylobates mahunkai Bayoumi, 1980 is discussed, resulting in the following new taxonomic proposal: Protoribates mahunkai (Bayoumi, 1980) n. comb.


Introduction
The oribatid mite genus Perxylobates of the family Haplozetidae (Acari, Oribatida) was proposed by Hammer (1972) with Xylobates vermiseta Balogh and Mahunka, 1968 as type species. According to Subías (online version 2020), the genus comprises 15 species, which are distributed in the Pantropical and Subtropical regions.
During taxonomic identification of oribatid mites from farmland with Ricinus communis in Taiwan, we found a new species, belonging to Perxylobates. The main goal of our paper is to describe and illustrate this new species. Hitherto, one perxylobatid mite species was registered in Taiwan, P. coreanus Choi andAoki, 1993 (Ermilov andLiao 2018).
The additional goals of our paper are to revise generic diagnosis and to provide an identification key to known species of Perxylobates, and to discuss the systematic placement of Perxylobates mahunkai Bayoumi, 1980.

Materials and methods
Specimens -Substrate samples containing oribatid mites were collected from the Biological Control Branch, Miaoli District Agricultural Research and Extension Station (Fig. 1) in Taiwan. Mites were extracted from samples into 75% ethanol using Berlese's funnels with electric lamps in laboratory conditions during 10 days.
As mentioned below in detail, types are distributed among two institutions: the National Taiwan University, Taipei, Taiwan (NTU); the Tyumen State University Museum of Zoology, Tyumen, Russia (TSUMZ). Observation and documentation -Specimens were mounted in lactic acid on temporary cavity slides for measurement and illustration. Body length was measured in lateral view, from the tip of the rostrum to the posterior edge of the notogaster. Notogastral width refers to the maximum width of the notogaster in dorsal view (behind pteromorphs). Lengths of body setae were measured in lateral aspect. All body measurements are presented in micrometers. Formulas for leg setation are given in parentheses according to the sequence trochanter-femurgenu-tibia-tarsus (famulus included). Formulas for leg solenidia are given in square brackets according to the sequence genu-tibia-tarsus.
Drawings were made with a camera lucida using a Leica transmission light microscope "Leica DM 2500".
Juvenile instars -Not known.
Legs (Figs 4a-c) -Monodactylous. Claw of all tarsi strong, slightly barbed on dorsal side, with tubercle ventrobasally. Tarsus I with longitudinal ridge distodorsally. Tibiae I and II with tubercle proximoventrally. Dorsoparaxial porose area on femora I-IV and on trochanters III, IV distinct. Proximoventral porose area on all tarsi and distoventral porose area on all tibiae not

Leg
Tr Fe Ge Ti Ta  Table 1. Famulus of tarsus I short, erect, slightly dilated apically, inserted between solenidion ω 2 and seta ft . Femur III and genu IV with reduced setation, with two and one seta, respectively (seta l absent). Some ventral setae (a, s, pv) on tarsi I-III thickened, with strong unilateral spines. Solenidion ω 1 on tarsus I, ω 1 and ω 2 on tarsus II and σ on genu III bacilliform, other solenidia setiform. Type deposition -The holotype is deposited in the collection of the NTU; four paratypes are deposited in the collection of the TSUMZ.
Etymology -The species name hakkai refers to the Hakka. Taiwanese Hakka people is the main population who lives in the type locality Miaoli County, Taiwan.
Remarks -Distinctive characters of the new species with the other species of the genus Perxylobates can be found in the identification key below.

Discussion
Perxylobates mahunkai was described by Bayoumi (1980) from Egypt and included in Perxylobates. However, this species differs from other representatives of the genus by the presence of a developed anterior notogastral margin (versus anterior notogastral margin completely absent in Perxylobates -generic characteristic). All morphological traits of P. mahunkai correspond to those of the genus Protoribates Berlese, 1908(e.g. Weigmann et al. 1993Bayartogtokh 2010), therefore we propose the following combination: Protoribates mahunkai (Bayoumi, 1980) n. comb.
Hence, at present, the genus Perxylobates currently comprises 15 species.

Key to known species of Perxylobates
We exclude Perxylobates longissimus (Warburton, 1912) (Seychelles) from the key because this species has been very briefly and insufficiently described.  (Balogh and Mahunka, 1968) (see also Hammer 1972