Desoria cooki Babenko & Fjellberg, 2025, sp. nov.

Desoria cooki sp. nov. Figs 17–27 Type material. Holotype (sex not checked), north-eastern Chukotka, Lavrentiya, spotted tundra, mosses, 65.5867°N, 171.0452°W, 13.07.2013. O. Makarova & A. Babenko leg. Paratypes, 22 specimens (including 16 juveniles), same area and collectors, but peat hillocks, 30.07.2013; 5 specimens (sex not checked) from hillock tundra, 28.07.2013; 4 specimens, same area, several different biotopes. Additional material. 7 specimens, same region, ~ 20 km west of Lavrentiya, mountain tundra with a dense cover of Alectoria, 27.07.2013. O. Makarova & A. Babenko leg.; 2 specimens (including 1 juvenile), vicinity of Anadyr airport (Ugolnye Kopi), rocky bank of a stream, near water, 02.07.2013. A. Babenko leg. Specimens of D. multisetis auct. used for comparison. Female, Canada, Ellesmere Is., Alexander Fjord, 03.08.1983, dry upland tussock tundra, Dryas, Carex, Salix, moss [310/83]. A. Fjellberg leg.; female, Canada, location unknown [33/84]. V. Behan leg.; 1 specimen (sex not checked), Alaska, Denali Highway, 120 mi, 29.07.1980, moss & grass at snow-edge, 4000 ft [85/80]. A. Fjellberg leg.; 1 specimen (sex not checked), Alaska, Cape Thompson, Odotoruk Creek Basin, 7– 11.08.1980, wet snow-bed meadow. D.A.B. Murray leg.; 1 specimen (sex not checked), Alaska, Canning River Delta, moss, swale, 23.07.1980, S.F. MacLean leg.; preadult male, Alaska, Nome, 01.09.1976, Sphagnum, Vaccinium, Ledum, Empetrum, lichens. R. Greenberg leg.; 2 specimens,Alaska, Eagle Summit, 01.08.1976, thick grass-turf on manured owl mound ~ 1200 m alt., A. Fjellberg leg.; 2 specimens, Alaska, 5.5 mi N of Franklin Bluffs, moist soil with Salix, moss, Arctostaphylos, Equisetum, 16.08.1976. A. Fjellberg leg.; 1 specimen (sex not checked), Alaska, steep Mt. across (E of) Galbraith Lake Camp, 18.08.1976, dry moss, lichens, Saxifraga, etc. in crevices on boulder [38]. A. Fjellberg leg.; 27 specimens, Chukotka, Magadan Region, Snezhnaya Dolina (AF-154 & AF-155), 20.08.1978. A. Fjellberg leg.; 1 specimen (sex not checked), western Chukotka, Pevek, Apapelgino, 69.8111°N, 170.6142°E, hill top, zonal association (mosses), 24.07.2018. O. Makarova & K. Makarov leg. Diagnosis.A species of the pJasini -group sensu Potapov (2001) of the genus Desoria, characterized by macrosetae densely ciliated all around, clearly serrated mesosetae and a fairly large number of tergal macrosensilla. Description. Body size up to 1.7–1.8 mm. Colour uniformly dark with numerous small lighter spots at bases of setae, ventral side lighter, dens and distal parts of legs more or less whitish. Body shape typical of the genus, Abd. V–VI clearly separated. Integument smooth, without visible granulation. Dorsal setal cover dense and strongly differentiated (Fig. 19), setal bases glandular as is typical of the group. Macrosetae rather long and densely ciliated all around (Figs 19, 22a), those on medial part of Abd. V about two times as long as tergum and 3–4 times as long as inner edge of hind unguis. Most mesosetae also more or less clearly serrated (Figs 22b–c), microsetae usually smooth and pointed (Fig. 22d). Dorsal macrosensilla distinctly differentiated, their number in juveniles being 77/66696 (Fig. 17), few additional macrosensilla usually present on some terga in adults, their position rather variable and some macrosensilla always present well in front of p-setae, especially on Abd. IV (Fig. 18). The number of microsensilla (11/111 ms) is typical of the group. Antennae longer than head. Ant. IV with a bifurcate subapical pin seta and a rather large spherical subapical organite in a pit (Fig 24). Ant. III organ normal, with some additional setaceous sensilla in apical row. Few similar sensilla also present apically on Ant. II and laterally on Ant. I, sensilla on the latter segment slightly thickened. Each side of head with 6 large and two smaller (G and H) ocelli. PAO broadly oval, about 1.5 as long as diameter of nearest ocellus. Labrum with 4/554 setae, apical edge with 4 sharp apical folds and a simple apical ciliation (Fig. 23). Central part of clypeal field with up to 10 setae. Maxillary outer lobe with a bifurcate palp and 4 sublobal setae. Labial palp with apical papillae A–E present, 4 proximal setae and all usual guards (16); terminal setae of the papillae subequal to the guards, lateral process on papilla E strong, finger-shaped; hypostomal papilla with H also about as long as h1/h2. Basomedial field of labium with 6(7) setae, basolateral one with 5 setae as usual. Head ventrally with 5–6 postlabial setae on each side of ventral line. Mandibles normal, with moderately strong teeth. Maxillae with tridentate capitulum and 6 short lamellae covered with fine denticles only. No ventral setae on thorax. Ventral tube with 7–12 frontal setae on each side, more than 10+10 lateral and up to 15 caudal setae with four setae in transversal apical row. Retinaculum with 4+4 teeth and 9–11 setae. Manubrium with a variable number of ventral setae and usually 4+4 short, slightly thickened, apical setae; ventroapical thickening usually simple (Fig. 20), rarely with a small subapical denticle (Fig. 21). Dens with numerous ventral setae, ventroapical one clearly elongated (Fig. 25). Dorsal side of dens with about 10 basal setae and 6–8 setae on each side of proximal half. Mucro typical of the group, with three subequal teeth (Figs 25). Tibiotarsi with 8(9) setae in apical whorl (Fig. 26), basal part of foreleg in adult and subadult specimens with three outer setae. Unguis with two clear teeth on inner edge and a pair of lateral ones basally; unguiculus about half as long as inner edge of unguis and usually with a corner tooth. Etymology. The new species is named after the British captain James Cook, who, in 1778, mapped and named the Bay of St. Lawrence (the region of the type locality of the new species) during his third circumnavigation of the globe. Affinities. The species is undoubtedly a new member of the Asiatic pJasini group, which has a number of features more typical of the genus Isotoma rather than Desoria (small PAO, two inner teeth on the unguis, reduced number of setae in apical row on tibiotarsi, mucro with three teeth, glandular base of setae), but it differs from representatives of Isotoma by the absence of spiny apical setae on the manubrium. At least 5 described species of this group are currently known: D. multisetis (Carpenter & Phillips, 1922), D. hissarica Martynova, 1968, D. tadzhika Martynova, 1968, D. zlotini Martynova, 1968, and D. pJasini (Martynova, 1974). Besides this, one Korean, i.e. D. choi (Lee, 1977), and two Chinese species, i.e. D. tianshanica Hao & Huang, 1995 and D. imparidentata (Stach, 1964), also seem to be related to this group (Potapov 2001). A real comparison is only possible with the former five species checked by Potapov (2001). The strongly ciliated macrosetae, four proximal setae on the labial palp (see Potapov 2001, p. 139, although only tree such setae was mentioned for Greenlandic specimens of D. multisetis by Fjellberg 2007) and 6(7) setae in the basomedial part of the labium clearly bring the new species closer to D. multisetis. The latter species was described from Northern Europe (Bjørnøya Island), and later also reported from Spitsbergen (Valpas 1967), Greenland (Fjellberg 2007, 2015), as well as Alaska, Canada and Chukotka (Potapov 2001). The latter author considered it as a complex of closely related species differing in mouth-part structure, sensillar chaetotaxy and other features which real position needs further study of the type specimens (p. 139). We have checked all material available to us on this species (see above) and can state that they do indeed differ in some features, the most obvious of which is the presence or absence of a free tooth on the manubrial thickening. At the same time, they all have only 55/444 macrosensilla on Th. II–Abd. III (vs 77/666 s in D. cooki sp. nov.), this corresponding to the description of this feature by Potapov (2001) and may, in our opinion, be a sufficient argument in favor of the independence of the described species. Distribution and ecology. The species was found in a wide variety of communities in two areas of northeastern Chukotka, the distance between which is about 500 km (Fig. 27).

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