Contribution to systematics of the genus Eustigmaeus (Acari: Stigmaeidae) of Russia

Two new species of Eustigmaeus: E. bochkovi n. sp., collected from rotten log in Khabarovsky Kray, and E. grandis n. sp., collected from soil in Primorsky Kray, are described from Russia. The genus Paravillersia Kuznetsov, 1978 is considered as a junior synonym of Eustigmaeus Berlese, 1910; Paravillersia grata Kuznetsov, 1978 is considered as a junior synonym of Eustigmaeus ottavii (Berlese, 1910), E. ioanninensis Kapaxidi and Papadoulis, 1999 is considered as a junior synonym of E. pinnata Kuznetsov, 1977a, and Paravillersia jamaliensis Khaustov, 2014 moved to the genus Villersia Oudemans, 1927.

During this study two new species, Eustigmaeus bochkovi n. sp. and E. grandis n. sp. were found from Khabarovsky and Primorsky Kray of Russia, respectively. The new species are described in this paper and new generic and species synonymies are also provided.

Materials and methods
The type materials of Eustigmaeus pinnatus and Paravillersia grata as well as specimens of Paravillersia grata and Eustigmaeus ioanninensis deposited in the collection of the Tyumen State University Museum of Zoology were examined. Specimens of Eustigmaeus bochkovi n. sp. and E. grandis n. sp. were collected from rotten wood and soil, respectively, using Berlese funnels and mounted on slides in Hoyer's medium.
Mite morphology was studied using a Carl Zeiss AxioImager A2 compound microscope with phase contrast and DIC objectives. Photomicrographs were taken with an AxioCam ICc5 digital camera. For SEM microscopy, alcohol-preserved mites were dried in freeze drying device JFD 320 (JEOL, Japan), dusted with gold and scanned with aid of a JEOL-JSM-6510LV SEM microscope.
All leg setae barbed (sometimes tc' smooth). Setae d of femur and genu distinctly blunt-ended, seta d of tibia weakly blunt-ended; other setae pointed.

Etymology
The specific name is given after the prominent Russian acarologist, Andrey Bochkov who passed away in 2018.

Differential diagnosis
The new species differs from all known species of Eustigmaeus by the presence of callosity located between endopodal plates of legs III and IV (absent in other species).

Type deposition
The holotype is deposited in the collection of the Zoological Institute of Russian Academy of Sciences, St. Petersburg, Russia. All paratypes are deposited in the collection of the Tyumen State University Museum of Zoology, Tyumen, Russia.

Etymology
The name of the new species is derived from Latin "grandis" meaning "large" and refers to very large body size.

Differential diagnosis
By the distinctly reticulate dorsal shields, similar shape of dorsal idiosomal setae and presence of two pairs of aggenital setae, the new species is most similar to E. changbaiensis (Bei and Yin), described from China by Bei & Yin (1995). The new species can be distinguished from E, changbaiensis by the presence of two pairs of callosities (only one pair in E. changbaiensis) and by much larger idiosomal length (385-435 vs. 285 in E. changbaiensis). Synonymy of the genera Paravillersia and Eustigmaeus Kuznetsov (1978) created monotypic genus Paravillersia with type species P. grata Kuznetsov, 1978. He noted that the genus Paravillersia has intermediate position between the genera Eustigmaeus Berlese, 1910and Villersia Oudemans, 1927. According to Kuznetsov (1978 the genus Paravillersia differs from Eustigmaeus by the location of setae sce on separate plate (on prodorsal shield in Eustigmaeus), and from Villersia by the location of setae d2 on hysterosomal shield (on separate plate in Villersia). Khaustov (2014) examined the holotype of P. grata and provided supplementary description of legs, gnathosoma and some idiosomal setae. During this study, I examined 6 female paratypes of P. grata deposited in the collection of the Tyumen State University Museum of Zoology, Tyumen, Russia. All type specimens of P. grata are squeezed and strongly flattened. Thus, some ventral and dorsal structures are visible almost in the same plane, especially in phase-contrast objective. In some type specimens of P. grata it seems that seta sce is located on separate plate (Fig. 18A). However, in DIC objective it is clearly visible that seta sce is located on prodorsal shield and only thin striated incision of the prodorsal plate visible anteriorly to seta sce (Fig. 18B). Numerous specimens of this species, collected from Western Siberia are also confirmed that seta sce is  Kuznetsov, 1978, female (paratype): A -anterior half of the body in dorsal view (arrows point to imaginary boundary between prodorsal plate and plate with seta sce), B -right half of prodorsum and anterior part of hysterosomal shield (arrows point to narrow incision anteriorly to seta sce). located on prodorsal shield. Based on the absence of morphological differences between the genera Paravillersia and Eustigmaeus, I consider the genus Paravillersia as a junior synonym of Eustigmaeus. The specific epithet of Eustigmaeus gratus (Kuznetsov, 1978) comb. nov. is modified according to masculine gender of the generic epithet. The second described species in the genus Paravillersia, P. jamaliensis Khaustov, 2014 moved to the genus Villersia Oudemans, 1927, because seta sce of this species is located on separate plate as in the genus Villersia. However, in Villersia jamaliensis (Khaustov, 2014) comb. nov. seta d2 located on hysterosomal shield (on separate plate in Villersia), but other characters are typical for Villersia.
Synonymy of Eustigmaeus gratus (Kuznetsov, 1978) comb. nov. and E. ottavii (Berlese, 1910) Eustigmaeus gratus (Kuznetsov, 1978) comb. nov. is characterized by the unique shape and location of callosities (see Fig. 7A in Khaustov 2014), baculiform and sparsely barbed dorsal idiosomal setae, presence of 3 pairs of aggenital setae and almost smooth dorsal idiosomal shields. Such combination (especially shape and location of callosities) of characters is known only in Eustigmaeus ottavii (Berlese, 1910) redescribed by Stathakis et al. (2016) and in E. isfahanensis Khanjani et al., 2014. Comparison of specimens of E. gratus from Russia with description of E. ottavii from Greece do not revealed any sufficient differences between these species. Therefore, I consider Eustigmaeus gratus (Kuznetsov, 1978) comb. nov. as a junior synonym of E. ottavii (Berlese, 1910). Potentially E. isfahanensis also could be a junior synonym of E. ottavii, but examination of the type material of this species is necessary. ps......_ 1 ~psi Figure 19 DIC micrographs of ano-genital area of females: A -Eustigmaeus pinnatus (Kuznetsov, 1977), holotype, B -Eustigmaeus ioanninensis, specimen from Western Siberia. Kapaxidi and Papadoulis, 1999 and E. pinnatus (Kuznetsov, 1977a) Eustigmaeus pinnatus (Kuznetsov, 1977a) was described from European Russia based on two females (Kuznetsov 1977a). This species is unique in having 4 pairs of pseudanal setae. I examined the female holotype of this species. It has abnormal number of aggenital and pseudanal setae. Left side of ano-genital area with 2 aggenital and 3 pseudanal setae, while right side with 3 aggenital and 4 pseudanal setae (Fig. 19A). Undoubtedly, the presence of unpaired additional pseudanal seta (ps on Fig. 19A) is abnormal. The normal number of pseudanal setae in Eustigmaeus is 3 pairs (Fan & Zhang 2005). The most similar species to E. pinnatus with normal 3 pairs of pseudanal setae is E. ioanninemsis Kapaxidi and Papadoulis, 1999. I compared female holotype of E. pinnatus with description of E. ioanninensis and specimens reported from Western Siberia (Khaustov & Tolstikov 2014) and did not find any sufficient differences. One female from Western Siberia identified as E. ioanninensis also has abnormal number of aggenital and pseudanal seta. Left side of aggenital area with 1 aggenital and 2 pseudanals, while right side with normal 3 aggenital and 3 pseudanal setae (Fig. 19B). Variability in number of setae in ano-genital area was also observed in Turkish specimens of E. ioanninensis (Bingül et al. 2017b). Based on the variability in number of setae in ano-genital area, I consider E. ioanninensis as a junior synonym of E. pinnatus.