Desoria verticillata, Babenko & Fjellberg, 2025

Desoria verticillata sp. nov.

Figs 28–39 View FIGURES 28–39

Type material. Holotype, female, Russia, Central Yakutia ( Sakha), Leno-Vilyui interfluve, Gornyi Ulus , Asyma , burnt Larix forest, 62.4003°N, 126.7931°E, 21.06.2024. A. Burnasheva leg. GoogleMaps Paratypes, 10 specimens (including 4 young instar juveniles), same biotope and collector, but 28.06.2022, 16.08.2023, 04.09.2023 & 14.07.24.

Additional material. Female , south-west Yakutia, Tokko River, 59.4724°N 120.1975°E, first floodplain terrace, 2011, V. Boeskorov leg.; two juveniles GoogleMaps , Suntar-Khayata Mt. Range , upper reaches of Kyubyume River, vicinity of «Vostochnaya» Meteorological Station, 63.2408°N, 139.6313°E, willow bushes in floodplain, 30.07.2002, O. Makarova leg. GoogleMaps

Diagnosis. A species of the violacea -group sensu Potapov (2001) (= hiemalis group sensu Fjellberg (2007)) of the genus Desoria , characterized by long, whorled serrated abdominal macrosetae, fused Abd. V–VI, and a manubrial thickening with a free tooth.

Description. Body size up to 1.9 mm ( holotype). Colour usually rather light, grayish with irregular lighter spots, the largest specimens probably darker. Ventral side and appendages also coloured similarly. Body shape typical of the genus, Abd. V–VI completely fused ( Figs 28 View FIGURES 28–39 ). Integument without visible granulation. Dorsal setal cover clearly differentiated into micro-, meso- and macrosetae. Macrosetae long and clearly serrated, those on medial part of abdominal tip 3.8–4.9 times as long as inner edge of hind unguis. Serrations on macrosetae usually arranged in regular whorls ( Fig. 29 View FIGURES 28–39 ). Dorsal accp-sens located slightly anterior to p-rows of setae on both thorax and abdomen; total number of dorsal macrosensilla in young specimens 66/5,5-6,5-6,6-7,5-6 ( Fig. 28 View FIGURES 28–39 ), slightly more in larger individuals, especially at the abdominal tip; Abd. IV always without macrosensilla in mid tergal position. The number and position of spine-like microsensilla typical of the group (11/111) ( Fig. 28 View FIGURES 28–39 ).

Antennae clearly longer than head. Subapical pin seta on Ant. IV bifurcate, subapical organite not especially large, but usually spherical ( Fig 30 View FIGURES 28–39 ) (see also Remarks). AO on Ant. III normal, with 4 dorsal and 2 lateral sensilla, sensillar equipment of other antennal segments also typical. Head with 8+8 ocelli, ocelli G and H smaller. PAO elongate, about 1.7–2.1 as long as diameter of nearest ocellus ( Fig. 31 View FIGURES 28–39 ). Labrum with 4/554 setae, apical edge with sharp apical folds and composite ventroapical ciliation, central part of clypeal field with up to 10 setae. Maxillary outer lobe with a bifurcate palp and 4 sublobal setae. Labial palp with all usual apical papillae (A–E) present, 4 proximal setae and 16 guards including e7 at base of papilla E; terminal setae on papillae more or less subequal to guards, lateral process on papilla E finger-like, shorter than papilla; hypostomal papilla with H also subequal to h1/h2. Both basomedial and basolateral fields of labium with 5 setae each. Ventral side of a head with 4–6 postlabial setae each side of ventral line. Mandibles and maxillae without visible modifications.

No ventral setae on thorax. Ventral tube with 6–8+6–8 frontal setae, 7–11+7–11 lateral and up to 14 caudal setae with four ones in apical row including two longer ones. Retinaculum with 4+4 teeth and up to 12–13 setae. Manubrium with numerous ventral setae including 2+2 short ones between apical macrosetae ( Fig. 32 View FIGURES 28–39 ); ventroapical thickening with a large free tooth ( Fig. 33 View FIGURES 28–39 ). Dens with numerous ventral (anterior) setae and up to 15–16 dorsal (posterior) ones in the proximal half ( Figs 34–35 View FIGURES 28–39 ), ventroapical seta not prolonged ( Fig. 36 View FIGURES 28–39 ). Mucro with four teeth, apical and subapical ones almost subequal, a lateral seta absent ( Fig. 36 View FIGURES 28–39 ). Tibiotarsi with 11 acuminate apical setae ( Fig. 37 View FIGURES 28–39 ), basal part of foreleg with three outer macrosetae and several additional microsetae ( Fig. 38 View FIGURES 28–39 ). Unguis with a clear inner tooth and a pair of lateral ones; unguiculus about half as long as inner edge of unguis, usually with a corner tooth ( Fig. 37 View FIGURES 28–39 ).

Etymology. The name of the new species reflects the unique whorled serration of the dorsal macrosetae (from the Latin verticillatus, meaning whorled or verticillate).

Remarks. At the type locality of the new species, one juvenile specimen was also found, which, unlike the described species, had weakly serrated macrosetae and a tiny, peg-like subapical organite ( Fig 39 View FIGURES 28–39 ). As seasonal morphological changes are quite typical for closely related species of the genus, possibly this is simply a cyclomorphic form of the same species, but a co-occurrence of closely related forms cannot be ruled out either.

Affinities. The new species is a fairly typical representative of the violacea group sensu Potapov (2001), possessing all of its characteristic features: labrum with sharp apical folds, complete labial palp with e7 present and four proximal setae, bifurcate maxillary palp, basomedial field of labium with 5 setae, short maxillary lamellae, ventral tube with 4 setae in the apical transverse row on posterior side, crenulated dens and mucro with four teeth and without lateral seta. Among the species of this group, only three species are known that, like D. verticillata sp. nov., show a free tooth on the manubrial thickening: D. neglecta ( Schäffer, 1900) , D. blufusata ( Fjellberg, 1978) and D. alaskensis ( Fjellberg, 1978) . Moreover, due to the fused last abdominal segments and long dorsal macrosetae, the new species is only comparable with D. alaskensis , which is not only sympatric, at least in the eastern Palearctic, but sometimes it also occurs in the same biotopes. In addition to the peculiar serration of the macrosetae and different coloration (light gray in D. verticillata sp. nov. and dark, almost black in D. alaskensis ), the new species is characterized by a lower number of dorsal sensilla (66/5,5-6,5-6,7,5- 6 in D. verticillata sp. nov. vs 77/6,7,7,12,9 in juvenile specimens of D. alaskensis including several ones in mid tergal position on Abd. IV [ thorax and abdomen with many accp-sensilla (7–9) according to Potapov (2001, p. 122)] and a smaller number of dorsal setae on dens ( 15–16 in D. verticillata sp. nov., vs 25–45 posterior (dorsal) setae, including several long ones in D. alaskensis according to Potapov (2001, p. 122)).

The North American fauna supports another species of the genus, D. randiella ( Fjellberg, 1978) , characterized by the presence of a free tooth on the manubrium, fused Abd. V–VI and rather long dorsal setae. However, clearly it is not close to the new species under consideration, being distinguished by a simple maxillary outer lobe, small and rounded apical folds on the labrum and an unusually sparse setal cover on the manubrium and dens.

Distribution and ecology. The species is apparently quite widespread, at least in Yakutia, and is known from three rather remote regions of this republic ( Fig. 40 View FIGURES 40 ), the maximum distance between which exceeds 1200 km.