Description of Orthadenella coulsoni sp. nov. (Acari: Mesostigmata: Melicharidae) from Siberia with a key to the females of Orthadenella

This paper presents both the description and the iconographic documentation of a mite species new to science: Orthadenella coulsoni sp. nov., recorded from Siberia, Russia. A key for determining females of all species within this genus is included. http://zoobank.org/urn:lsid:zoobank.org:pub:3B416529-A22D-43B3-96BD-3D5A8ED4F0F1


Introduction
The genus Orthadenella was described originally by Athias-Henriot (1973) who established the genus Proctolaelaps (Neojordensia) lawrencei described by Evans (1958). Although Athias-Henriot in her elaborate paper (1973) distinguished between genera Orthadenella and Neojordensia, in subsequent works this proposal was disregarded, thus the previous classification structures have remained (Bregetova 1977;Karg 1993;Gwiazdowicz 2007). Christian and Karg (2006) in their monograph elaborate on the genus Lasioseius, placed Lasioseius lawrencei in the subgenus Lasioseius s. str., within a group labelled as Lasioseius-berlesei-complex. Some changes were made along with a new classification proposed by Lindquist et al. (2009) in which attention was paid to the two species of the genus Orthadenella. Lindquist and Moraza (2010) revised the differential characters of the Blattisociidae, and provided a key to the genera, placing Orthadenella within this family. In the next paper the same authors removed Orthadenella from the family Blattisociidae and transferred it to the family Melicharidae (Moraza and Lindquist 2011).
At present two species of Orthadenella are known; Orthadenella lawrencei (Evans 1958) and O. tennesseensis (De Leon 1963). Unfortunately, the biology and ecology of these are poorly known. Previously, O. lawrencei was recorded from many European countries occurring in microhabitats such as forest litter, humus, moss on soil and on tree trunks and rotting wood (Gwiazdowicz 2007). The latter species, O. tennesseensis, is recorded in North America in moss, hardwood logs, pine trees attacked by scolytid bark beetles, and bracket fungi (De Leon 1963;McGraw and Farrier 1969).

Materials and methods
Nineteen females and eight males of an undescribed species belonging to the genus Orthadenella were found in litter from the Altai Mountains in the southern Siberia, Russia.
Mites were removed from litter and soil samples by the Tullgren funnel extraction method, and preserved in 70% ethanol. These were mounted in Hoyer's medium on glass slides for identification and sealed with a nail polish. All figures were drawn using a Zeiss Axioskop 2 microscope (Carl Zeiss AG, Jena, Germany). Morphological details were measured as follows: setal length from base to tip, shield length along midline and width at the widest point of the shield. All measurements are in micrometres (μm). The chaetotaxy, symbols and the numbering system of setae on the dorsal and ventral side are after Evans (1963), Lindquist and Evans (1965) and Lindquist (1994). The idiosomal adenotaxy and poroidotaxy are based on Johnston and Moraza (1991).
The holotype, four paratypes of females and four paratypes of males are deposited in the Siberian Zoological Museum in Novosibirsk, Russia; 14 paratypes of females and four paratypes of males are deposited in Natural History Museum in London, UK.

Diagnosis of genus
Dorsal side. Idiosoma with a holodorsal shield, 11 pairs of marginal r-R setae on edge of dorsal shield, the opisthonotal region of shield with 20 pairs of setae, seta z1 present.
Ventral side. One or two pairs of presternal platelets, sternal shield with three pairs of simple setae, one pair of metasternal platelets, ventrianal shield, one or two pairs of metapodal platelets, endopodal shields alongside coxae III-IV are strongly developed, and are contiguous or connected with the endopodal portions of the sternal shield alongside coxae II, peritrematal shields connected with a continuous, unfragmented exopodal strips alongside coxae IV; spermathecal apparatus with two branches of tubulus annulatus, unpaired sacculus foeminus, and narrow sperm duct; sacculus walls with many thin filaments or cylindrical protrusions.
Gnathosoma. Corniculi well separated, stout; deutosternal groove with rows, each with 2-6 denticles; movable cheliceral digit with three denticles, fixed digit with a ridge extending from paraxial surface to 3 denticles on proximoventral surface, bears a setiform pilus dentilis, instead of the modified hyaline process typical for the great majority of melicharids; epistome convex or triramous, denticulate.

Etymology
The species is dedicated to our friend, a scientist exploring the invertebrate fauna of the High Arctic, Prof. Dr Stephen J. Coulson from University Centre in Svalbard. Longyearbyen, Norway.

Differential diagnosis
The morphometric analysis of O. coulsoni shows many different diagnostic characters from the other two species of Orthadenella. Even a simple analysis of setae measurements gives both similarities (the same lengths of setae Z4, Z5, and setae J1, J2, J3, J4, Z1, Z2 longer by 6-7 μm, and vertical j1 shorter by 4 μm) and dissimilarities when compared to O. tennesseensis. A shared character between O. coulsoni and O. lawrencei is a marked dorsal reticulated patterning covering almost the whole shield, while in O. tennesseensis, this is reticulated only on the posterior and anterior border. Moreover, O. coulsoni and O. lawrencei have a humeral seta r3 conspicuously longer than the remaining setae in the marginal row r-R, which O. tennesseensis does not. This character is repeated in the S4, S5 and Z5 pairs of setae. However, O. lawrencei setae Z4 are identical to the Z1-Z3 setae, whereas in O. coulsoni these setae are dissimilar. In addition, the location of pore iv5 is a further diagnostic character. This pore lies outside the genital shield of both O. coulsoni and O. tenessensis but, as is more common, on the shield in O. lawrencei. A very fine character separating the species is the appearance of a ventrianal shield. This has a characteristic concave anterior boarder at the level between the genital and metapodal sclerites for the entire genus, but differs in shape among species. That of O. coulsoni is wider than long, contrary to the other species. Likewise, the difference in the number of setae located on the ventrianal shield, excluding a circum-anal setae, is another significant character, differentiating O. tennesseensis, with five pairs, from the two remaining species, each bearing six pairs. The metapodal shields in the opistogastric region clearly distinguish O. lawrencei which possesses only a single pair, while O. coulsoni has two pairs composed of the larger sclerite with a smaller abutting. The epistome of O. tennesseensis and O. lawrencei is a trispinate, median process broadly triangular and extending beyond the apex of the lateral processes, contrary to O. coulsoni, which has convex epistome with homogenous denticles arranged parallel to each other. The spermatheca of O. lawrencei is composed of a sacculus permeated with numerous pores and cylinders, while the spermatheca of O. coulsoni is permeated with numerous pores and thin filaments.
Key to the females of genus Orthadenella Information concerning O. lawrencei and O. tennesseensis was obtained from published descriptions and illustrations (Evans 1958;De Leon 1963;McGraw and Farrier 1969;Moraza and Lindquist 2011).