A new wood-inhabiting mite species of the genus Dendroseius Karg, 1965 (Acari, Mesostigmata, Rhodacaridae) from Central Europe (Slovakia)

Abstract A new rhodacarid mite of the genus Dendroseius Karg, 1965, D. reductussp. nov., was described based on females found in wood detritus and under bark of dead and dying poplar trees in a flood-plain forest in South Slovakia. The new species is unusual among the known congeners in the specifically formed triramous epistome of which the central projection is reduced in length, truncate, and markedly shorter than lateral ones. In other congeneric species, the anterior margin of the epistome possesses three pointed projections of similar size. A dichotomous key for identification of females of the world species classified in the genus Dendroseius is provided.


Introduction
Dendroseius was originally described as a subgenus of Dendrolaelaps Halbert, 1915 by Karg in 1965, and treated at the generic level by Hirschmann (1974), Lindquist (1975), Evans and Till (1979), Shcherbak (1980), Karg (1993), and other acarologists. The modern concept of Dendroseius is largely based on above cited authors who separated the genus from other "Dendrolaelaps-like" genera primarily by the following diagnostic character states: (1) dorsal setae j2 with more posterior position, situated between setae j1 and j3, not in a transverse setal row between j1 and z1; (2) gnathosomal groove on deutosternum with seven transverse furrows of which none is reaching beyond the lateral borders of the groove; (3) movable digit of chelicera with three teeth in addition to the apical hook; (4) straight anterior margin of opisthonotal shield; (5) sperm induction system associated with coxae IV.
The purpose of this study is to describe a distinct new species of Dendroseius from Slovakia contributing thus to knowledge of Rhodacaridae European fauna. Our finding represents also a first record of the genus Dendroseius for Slovakia. An introduction of a new key to the identification of the world species based on females is a supplementary aim of this paper.

Materials and methods
The mites were extracted from decomposing wood detritus by means of a modified Berlese-Tullgren funnel equipped with a 40-Watt bulb, and preserved in ethyl alcohol. Some specimens were collected by wet pincette from under loosen bark. Before identification, the mites were mounted onto perma nent microscope slides, using Swan's chloral hydrate mounting medium. A Leica DM 1000 light microscope equipped with a Leica EC3 digital camera was used to obtain measurements and photos. Measurements were made from slide-mounted specimens. Lengths of idiosoma and shields were measured along their midlines, and widths at their widest point (if not otherwise specified in the description), legs I-IV from coxal base but without the pretarsal ambulacrum. Idiosomal setae were measured from the bases of their insertions to their tips. Measurements are mostly presented as ranges (minimum to maximum). The terminology of dorsal and ventral chaetotaxy follows Lindquist and Evans (1965), and that for leg and gnathosomal setae follows that of Evans (1963aEvans ( , 1963b.
Sperm induction system (Fig. 10). Each gonoporus associated with inner posterior margin of coxa IV, together with relatively short and broad duct formed as a clubshaped structure; the duct opening into small hyaline sacculus. Sperm system of both coxae mutually connected with membranous structure (Fig. 10).
Etymology. The specific name is derived from the Latin word reductus (reduced) and expresses an important feature of the species -an unusual shape of epistome, a fine flat structure situated on upper surface of gnathosoma, with partly reduced central projection on its anterior margin.
Taxonomic notes. The triramous epistome of the new species, with remarkably shortened central projection, is unique and quite unlike any other known species in the genus Dendroseius. In other congeners, this central projection is much longer and more acuminate in the terminal part, reaching to (in D. amoliensis) or slightly beyond the level of the adjacent lateral apices (in all other congeners, including two species exclusively based on deutonymphs and not included in the key below). Nevertheless, the new species is most similar to D. vulgaris distributed in China (Ma, Ho and Wang 2014), and it can be distinguished from D. vulgaris and other species by the character states presented in the identification key below. Some metric data for D. reticulatus provided in the key are derived from specimens in author's personal collection from Wales, UK (Anglesey, Newborough Beach, found in decomposing plant substrate in a sandy coastal area). The morphological data used for other Dendroseius species were based only on the original descriptions.
Key to world species of Dendroseius (females)