A review of myrmecophilous mites of the family Microdispidae (Acari, Heterostigmatina) of Western Siberia

Abstract Five species of myrmecophilous microdispid mites (Acari: Microdispidae) are recorded from Western Siberia, Russia. Unguidispus lasii Kurosa, 1979, Unguidispus japonicus Kurosa, 1979, Caesarodispus minutus (Sevastianov, 1981), and Caesarodispus samsinaki (Mahunka, 1967), comb. n. are reported from Russia for the first time. Unguidispus polyctenus (Sevastianov, 1969) and Caesarodispus samsinaki are redescribed. The keys to species of the genera Unguidispus Mahunka, 1970 and Caesarodispus Mahunka, 1977 are provided.


Introduction
The family Microdispidae Cross, 1965 (Acari: Pygmephoroidea) includes 18 genera and about 115 described species (Hajiqanbar and Hosseininaveh 2014). All representatives from the genera Unguidispus Mahunka, 1970, Caesarodispus Mahunka, 1977, Myrmecodispus Cross, 1965, Reductodispus Mahunka, 1977, Perperipes Cross, 1965, and Glyphidomastax Cross, 1965 are associated with various ants (Hymenoptera: Formicidae) (Hajiqanbar and Hosseininaveh 2014). Most of microdispid mites are fungivorous, but the species from the genera Perperipes and Glyphidomastax, associated with army ants, probably feed on their larvae and/or eggs (Kaliszewski et al. 1995). During the study of myrmecophilous mites of Western Siberia we found five species of the family Microdispidae belonging to the genera Unguidispus Mahunka, 1970 andCaesarodispus Mahunka, 1977. The main goal of this paper is to redescribe the poorly known species Unguidispus polyctenus (Sevastianov, 1969) and Caesarodispus samsinaki (Mahunka, 1967), comb. n. and provide new records of myrmecophilous microdispid mites from Western Siberia, as well as the keys to world species of the genera Unguidispus and Caesarodispus.

Materials and methods
Mites were collected from ants or ant nests and mounted in Hoyer's medium. The terminology of idiosoma and legs follows Lindquist (1986); the nomenclature of subcapitu lar setae and the designation of cheliceral setae follow Grandjean (1944Grandjean ( , 1947, respectively. The system of Pygmephoroidea follows Khaustov (2004Khaustov ( , 2008. All measurements are given in mi crometers (μm). For leg chaetotaxy the number of solenidia is given in parentheses. The studied material is deposited in the mite collection of the Tyumen State University Museum of Zoology, Tyumen, Russia. SEM photographs were made with the aid of JEOL-JSM-6510LV SEM microscope.
Male and larva unknown. Distribution and hosts. This species was described from Western Ukraine from ants Formica polyctena Forster (Sevastianov 1969). It was also recorded in northwestern Russia (Sevastianov 1978), Austria (Mahunka 1970b) from ants Formica rufa L., and in Hungary from ant nest (Mahunka 1987).
(Neopygmephoridae) which he considered as a senior synonym of Piniphorus. The same year Mahunka (1970b) moved this species to the microdispid genus Unguidispus Mahunka, 1970. In spite of this, Sevastianov (1978) retained it in the neopygmephorid genus Xystrorostrum.
The original description of U. polyctenus of Sevastianov (1969) is incomplete, thus I made a redescription of this species. The present redescription of U. polyctenus is based mainly on material from Western Siberia. The female paratypes available for this study are found in bad condition, yet sufficient to prove their identity with mite specimens from Western Siberia.  (Sevastianov, 1969), female: A leg III B leg IV. Kurosa, 1979 Unguidispus lasii Kurosa, 1979, p. 66, figs 5-6. This species was described from Japan where it was found in the nests of ants Lasius niger and L. hayashi Yamauchi and Hayashida (Kurosa 1979). I recorded phoresy of this species on Lasius niger in Western Siberia. This is a new record for the fauna of Russia.  (Sevastianov, 1969), female, SEM photos: A dorsum of the body B lateral view of the body C tergites EF and H D venter of the body E gnathosomal capsule F legs I and distal part of gnathosoma laterally. Kurosa, 1979 Unguidispus japonicus Kurosa, 1979, p. 64 This species was described from Japan from the nests of ants Lasius niger (Kurosa 1979). I recorded phoresy of this species on Lasius niger in Western Siberia. This is a new record for the fauna of Russia.  Mahunka, 1977, by original designation. Diagnosis. Female. Gnathosoma dorsally with two pairs of setae. Pharyngeal pumps 1 and 3 vestigial, pharyngeal pump 2 large, transversely striated. Prodorsum usually almost completely covered by tergite C. Cupules ia and ih small, usually round. Two pairs of pseudanal setae (ps 2 absent). Posterior margin of posterior sternal plate entire. Leg I distinctly shorter than leg II. Tibiotarsus without claw; pinnaculum absent; setae s of tibiotarsus I present. Trochanter IV anterodorsally without spinelike process.
Idiosomal venter (Fig 5B). All ventral plates with small dimples. Posterior part of posterior sternal plate and aggenital plate reticulated. All ventral setae pointed and barbed. Ap1 well-devel oped and joined with appr; ap2 thin, arch-like, fused with appr; appr and apsej well developed; ap3 indistinct. Ap4 well sclerotized and long, apodemes 5 absent. Posterior margin of posterior sternal plate slightly convex in middle part. Posterior margin of aggenital plate rounded. Ags bell-like, pgs elongate, subtriangular.
Male and larva unknown. Material examined. One female, RUSSIA: Tyumen Province, vicinity of Tyumen, 57°04'03"N, 65°04'12"E , on ants Formica rufa L., 17 August 2014, coll. A.A. Khaustov. Distribution and hosts. This species was originally described from the Czech Republic (Mahunka 1967) where it was collected from ants Formica rufa. It was also recorded from Ukraine and Belarus (Sevastianov 1978). This is a new record for the fauna of Russia.
According to key to families of the superfamily Pygmephoroidea provided by Khaustov and Ermilov (2011) this species undoubtedly belongs to the family Microdispidae by having three setae on femur I, unmodified seta dFeI and presence of only one pair of setae on prodorsum. I placed this species in the genus Caesarodispus based on the following combination of characters: 1) tibiotarsus I without claw, 2) leg I distinctly shorter and thinner than leg II, 3) seta s of tibiotarsus I present, 4) pharyngeal pumps 1 and 3 vestigial, pharyngeal pump 2 large, distinctly transversely striated, 5) posterior margin of posterior sternal plate entire. All of these characters well agree with diagnosis of the genus Caesarodispus.
Unlike other known species of the genus Caesarodispus, C. samsinaki has only two setae on femur II (v" absent) and only three solenidia on tibiotarsus I (ω 2 absent). However reduction of leg chaetotaxy was also recorded in C. klepzigi Khaustov and Moser, 2008, which has only two setae on femur I, while other Caesarodispus species have three setae.

Caesarodispus minutus
This species was described from Ukraine from ants Tetramorium caespitum L. (Sevastianov 1981). Khaustov (2009) redescribed it based on type material. It was also recorded from Iran from Temnothorax sp. (Loghmani et al 2014). This is a new record for the fauna of Russia.