﻿A new digamasellid mite of the subgenus Longoseiulus Lindquist (Acari, Mesostigmata) from Slovakia

﻿Abstract A new digamasellid mite, Longoseius (Longoseiulus) disparisetussp. nov., was described from females found in the wood detritus of tree cavity of freshly felled elm (Fraxinus sp.) in a park in southwestern Slovakia. The new species differs from known congeners by the number of setae on some leg segments (genu II with eight setae, tibiae II and III with seven and six setae, respectively) and by the unusual presence of three pairs of conspicuously shortened setae (J3, J4, and Z3) on the posterior dorsal shield. In other known Longoseiulus species, the genu II has 11 setae, the tibiae II and III have 10 and seven setae, respectively, and almost all dorsal setae are of similar length (except for the elongated Z4 and S4), none of which is formed as a microseta. A dichotomous key for females is provided to identify species classified worldwide in Longoseiulus.

The concept of Longoseiulus adopted here is largely based on the diagnosis of Lindquist (1975) and mainly on the following characters: (1) leg III with four setae on trochanter instead of normally five setae, and with seven or fewer setae on genu and tibia instead of eight or nine setae; (2) basitarsi II and III each with two or three setae instead of normally four setae, basitarsus IV with one to three setae instead of normally three or four setae; (3) hypostomal furrow of gnathosoma with most proximal fifth row of denticles not distinctly wider than preceding rows (in other genera this fifth row of denticles is conspicuously wider than preceding rows, or six rows of denticles of similar width are rarely present); (4) four-toothed movable digit of female chelicerae; (5) setae j2 transversely aligned with j1 and z1 on podonotal shield; (6) sclerotized anterior margin of opisthonotal shield with a deep double incision in the middle; (7) peritreme of adults and deutonymphs similar in length, shortened and extending at most only slightly beyond posterior margin of coxa II.
The subgenus Longoseiulus Lindquist, 1975 is a small group of digamasellid mites and currently includes only seven known species from Europe (aberrans, longuloides, longulus, ornatus), Asia (nobilis, ornatosimilis), and North America (brachypoda), which are almost always found in saproxylic habitats, especially in decomposing wood of various coniferous and broad-leaved deciduous trees, and in subcortical spaces associated with galleries of bark-and wood-boring beetles. Phoretic activity of deutonymphs is common in many xylophagous beetles such as Cerambycidae, Cleridae, Elateridae, Scolytinae, and Pyrochroidae (Hirschmann and Wiśniewski 1982).
The aim of this study is to describe a new species of the subgenus Longoseius (Longoseiulus) from Slovakia and thus to contribute to the knowledge of the fauna of Digamasellidae in Europe. This work is part of a project aimed at increasing our collective knowledge of the mite fauna of Slovakia. In this sense, the finding of the new species also represents a first record of the genus Longoseius for Slovakia.

Materials and methods
Mites were extracted from decomposing wood detritus using a modified Berlese-Tullgren funnel equipped with a 40-W lamp and preserved in ethyl alcohol. For identification, the mites were mounted on slides with Swan's medium (gum arabic/ chloral hydrate). A Leica DM 1000 light microscope with a Leica EC3 digital camera was used for measurements and micrographs. The photomicrographs were processed using Adobe Photoshop Elements 8 software. Measurements were made on specimens mounted on a microscope slide. Idiosoma and shield lengths were measured along their midlines, and widths were measured at their widest point (unless otherwise noted in the description). The lengths of the ventral idiosomal shields are midline, from the anterior to the posterior margin of each structure, including the hyaline anterior extension of the epigynal shield and excluding the posterior cribrum of the anal shield. Legs were measured excluding the ambulacral apparatus. Setae were measured from the bases of their attachments to their tips. The dimensions of the structures are given as ranges (minimum to maximum). The number of teeth on the cheliceral digits does not include the apical hook. Setal notation symbols for the idiosoma follow Lindquist and Evans (1965), slightly modified by Lindquist (1994), and notation symbols for leg setae follow Evans (1963). Terminology for the other anatomical structures follows Evans and Till (1979). The chaetotaxy symbols used here are shown in Figs 1, 2. There are other important diagnostic characters for this new species: (1) the absence of dorsal setae r5 (these setae are present on the soft cuticle in females of the related species whose setae Z3 are prominent and moderately elongate), (2) the absence of many leg setae that Lindquist (1975) indicated in his original definition as being present in Longoseiulus species, possibly based on the chaetotaxy of the type species Longoseius (Longoseiulus) longulus. There is one other species of Longoseiulus for which Hurlbutt (1967) originally reported the chaetotaxy of the legs, namely L. (L.) brachypoda. In comparison with the above species, the new species was found to have setal deficiencies in the following leg segments: genu II with eight instead of 11 setae, tibia II with seven instead of 10 setae, tibia III with six instead of seven setae, and telotarsi II and III with 11 instead of 12 setae. For a further comparison of the chaetotaxy of the legs of the new species with those of the subgenus Longoseius, see Table 1. (Figs 1, 8). Idiosoma 310-335 μm long and 140-155 μm wide (six measured specimens), narrowly oval, only moderately elongate, rounded anteriorly and posteriorly, suboval, widest in anterior part, at level of anterior ends of peritremes. Dorsal shield completely divided into podonotal and opisthonotal parts, not completely covering the dorsal surface, exposing narrow strips of lateral soft cuticle. Podonotal shield 153-167 μm long and 106-121 μm wide, anteriorly and posteriorly broadly rounded, with smooth and unornamented surface (not considering sigillae, sclerotic nodules, and some fine and very short lines on anterolateral areas), 18 pairs of setae (j1-j6, z1-z6, s1-s6) and two pairs of usually crescent-shaped subsurface sclerotic nodules between setae z5 (the outer pair with larger and more conspicuous nodules than the inner pair of contiguous nodules arranged anteriorly). Two pairs of anterior marginal setae present, namely r3 on peritrematal shields and r4 on soft cuticle between podonotum and peritrematal shields. Opisthonotal shield 147-166 μm long and 76-93 μm wide (excluding lateral strips of scutal elements), anteriorly and posteriorly broadly rounded, laterally straight and nearly parallel, largely smooth except for a small foveolate area between setae Z4, with 15 pairs of setae (J1-J5, Z1-Z5, S1-S5); anterior margin of wellsclerotized part of shield with two deep medial incisions, flanked by narrow band with nearly desclerotized margin. Four pairs of posterior marginal setae present: R1 on soft cuticle adjacent to anterolateral margins of opisthonotum; R3 and R4 on narrow longitudinal bands of scutal elements parallel to lateral margins of opisthonotal shield and narrowly fused to posterolateral margins of shield; R5 usually on soft integument on ventral side near setae JV5 or rarely on margin of opisthonotal shield. All dorsal setae smooth and needle-like, usually similar in length; three pairs of setae (J3, J4, and Z3) conspicuously reduced in length and each formed as a microseta (2-4 μm long); S5 longest (37-48 μm); lengths of other dorsal setae as follows: j1-j6, z1-z6, s1-s6, r4, J1, J2, Z1, Z2, and S1-S4 = 7-11 μm; J5, Z4, R1, R3, and R4 = 5-7 μm; Z5 = 22-30 μm; r3 and R5 = 10-14 μm.  Hurlbutt (1967), Lindquist (1975) and own data]. Explanations: * -new information for a diagnosis of the subgenus Longoseiulus, ** -new information for a diagnosis of the genus Longoseius. Ventral idiosoma (Figs 2,3,9,10). Tritosternum with short columnar base and two laciniae; laciniae divided to base, each sparsely, finely and shortly pilose. Sternal shield weakly sclerotized and defined (compared to epigynal and ventrianal shields), longer than wide, with two lobe-shaped anterior extensions each bearing a seta (st1), four pairs of sternal setae (st1-st4), and three pairs of poroidal structures; st3 more closely spaced than the other pairs of sternal setae; posterior margin moderately concave and shaped into posterolateral angles, each bearing a metasternal seta (st4); shield smooth over entire surface, except for small desclerotized areas lateral to st1, each with three to five short lines (Figs 3, 9). Epigynal shield elongate, 81-93 μm long, widest at anterior hyaline part (48-55 μm), formed as convex and moderately trilobate marginal structure, narrowest at level of st5 (27-33 μm), slightly rounded posteriorly, with a pair of genital setae (st5) near posterolateral margins and a pair of genital poroids posterior to st5. Exopodal and endopodal plates or platelets not developed, absent. Peritremes usually with dorsolateral to lateral position on idiosoma (Fig. 1), shortened, 67-84 μm long, each with anterior end extending slightly beyond posterior margin of coxa II. Peritrematal shield developed only along anterior part of peritreme (r3 captured by shield), narrowly connected to podonotal shield at level of s3, completely reduced along posterior part of peritreme and weakly developed near stigma, with very short poststigmatic part. A pair of strongly elongated and longitudinally oriented metapodal platelets present; platelets narrow, 34-42 μm long and slightly curved. Ventrianal shield expanded posteriorly, vase-shaped, distinctly longer than wide (69-80 μm long and 49-58 μm wide), with nearly straight anterior margin, broadly rounded posterior margin, smooth surface, four pairs of preanal setae (JV1-JV3, ZV2) in addition to three circum-anal setae and one pair of gland pores located near posterior margin at level of postanal seta (pa); adanal setae (ad) at least twice as long as postanal seta (ad 18-25 μm, pa 8-12 μm); anus and cribrum relatively small. Soft opisthogastric cuticle with three pairs of preanal setae (ZV1, ZV3, and JV5). Ventral setae similar in form to those on dorsal side of idiosoma, with the following lengths: st1-st5, JV1-JV3, ZV1 and ZV2 = 8-11 μm, ZV3 = 5-7 μm, JV5 = 12-16 μm.

Description (female). Dorsal idiosoma
Sperm induction system (Fig. 4). Sperm duct relatively well sclerotized, long and wide, located within the coxa, trochanter, and femur of legs III, apparently bifurcate near its terminal part, and opened at level of distal part of femur III.

Legs
Taxonomic note. Among the closest relatives with known chaetotaxy of the legs, the new species is easily recognised by the specific number of setae on several leg segments (see Table 1 and the above diagnosis). It lacks many leg setae that Lindquist (1975) indicated in his original definition as being present in Longoseiulus species, namely al, ad3, pl on the genu II; al, ad2, pl on the tibia II; pl on the tibia III; and md on the telotarsi II and III. This requires some amendments to the diagnosis introduced by Lindquist (1975) for Longoseiulus and partially for the genus Longoseius (a pl seta found on the tibia III in Longoseius cuniculus Chant, 1961 is absent in the new species).
Etymology. The specific name is derived from the Latin words dispār (unequal or dissimilar) and sēta (bristle or hair) and refers to the striking differences in length between the setae on the opisthonotal shield of the female of this new mite (three pairs of setae are greatly reduced and formed as microsetae).
Key to the worldwide species of the subgenus Longoseiulus (females) Longoseiulus includes seven described species, all known from the Holarctic. Only Longoseius (Longoseiulus) aberrans Hirschmann, 1960 is not included in the following key because its description is based solely on the male stage (it is one of the species with 21 pairs of setae on the anterior dorsal surface, including r5). It is not possible to reliably subdivide the individual species of Longoseiulus known to date based on literature data alone, without examining the type specimens. They should be thoroughly revised, redescribed, and compared in future studies to obtain a more accurate and reliable identification key than the one presented in this study. The original descriptions of most Longoseiulus species were not elaborated with the necessary precision (for example, they lack information on the chaetotaxy of the legs or on the measurement of important setal or scutal structures). Therefore, it is not currently possible to define and delimit some species morphologically on the basis of reliable characters. It is likely that a future revision will reveal the conspecificity of some species now placed in this subgenus.