Desoria nordenskioldi, Babenko & Fjellberg, 2025

Babenko, Anatoly & Fjellberg, Arne, 2025, Three new Desoria species (Hexapoda, Collembola, Isotomidae) from the eastern Palaearctic, Zootaxa 5717 (1), pp. 85-99 : 86-89

Desoria nordenskioldi sp. nov.

Figs 1–16

Type material. Holotype, female, western Chukotka, Pevek, Apapelgino , 69.8111°N, 170.6142°E, upper part of hill slope, Dryas association, 24.07.2018, O. Makarova & K. Makarov leg. Paratypes, 20 specimens (slides, sex not checked) from the same biotope; 16 specimens (including several juveniles), same area, date and collectors, but zonal plant association with Vaccinium uliginosum .

Additional material. 2 specimens, western Yakutia ( Sakha) Republic, Olenek Bay, Baganytta-Kyuel Lake, 73.50°N, 118.167°E, spotted tundra, moss trough, 06– 08.07.1994; 4 specimens, same Republic, delta of Yana River, Shirokostan Peninsula, 72.42°N, 141.00°E, spotted tundra on rocky soil, 04– 06.07.1994; 2 specimen, same region and date, but dry moss/lichen rocky slope and peat rim in bog; 3 specimens, Novosibirsk Islands, Faddeev Is., 75.58°N, 144.83°E, zonal spotted tundra, 10– 11.07.1994; 6 specimens (slides) and 11 specimens (alcohol), same archipelago, Kotelnyi Is., Balyktakh River, 75.05°N, 140.17°E, elevated rim in polygonal swamp (96/94), 31.07– 02.08.1994; 6 specimens, Indigirka River delta, 71.43°N, 149.75°E, lemming colony, grasses, 14– 16.07.1994; 5 specimens, Kolyma River delta (left bank), Pokhodskaya Edoma, 69.53°N, 160.73°E, Vaccinium vitis-idaea association on slope, 18– 19.07.1994, all A. Babenko leg.; 8 specimens, Yakutia ( Sakha) Republic, Suntar-Khayata Mt. Range, upper reaches of Kyubyume River, vicinity of «Vostochnaya» Meteorological station, 63.2408°N, 139.6313°E, larch forest with Sphagnum , ~ 1400 m alt., 24.07.2002, O. Makarova leg.; 2 specimens, same area and collector, but litter under dwarf pine, 1470 m. alt., 07.07.2002; 3 specimens, same region, vicinity of Tiksi, 71.6182°N, 128.9189°E, dwarf Betula shrubs, 22.08.2015, A. Nekhaeva leg.; 4 specimens (slides), Magadan Region, upper current of Kolyma River, Aborigen field station, 61 o 56'N, 149 o 40'E, moss and Larix / Pinus litter on slope down to stream (AF-79), 25.07.1979, A. Fjellberg leg.; 26 specimens (alcohol), same area and collector, but deep, moist litter in dense thickets of Pinus pumila at field station, ~ 1200 m, 27.07.1979 (AF-97).

Diagnosis. Species of the tigrina -group sensu Fjellberg (2007) of the genus Desoria , characterized by fused Abd. V–VI, long smooth macrochaetae and a low number of tergal macrosensilla.

Description. Body size up to 1.6 mm. Colour usually uniformly dark with few irregular lighter spots, but lighter specimens also exist. Blue-violet pigment evenly distributed throughout the body, antennae also intensely coloured, dens and distal parts of legs more or less whitish. Body shape typical of the genus, Abd. V–VI completely fused ( Fig. 1 ). Integument smooth, without visible granulation. Dorsal setal cover dense and strongly differentiated ( Figs 2–3 ), especially on last abdominal segments ( Fig. 4 ). Macrosetae smooth, pointed and usually slightly thickened at base, those on medial part of Abd. V about three times as long as inner edge of hind unguis. The number of dorsal macrosensilla strongly reduced: only 33/21113 s in the p-row on abdomen and 10/001 spine-like microsensilla present ( Fig. 1 ).

Antennae slightly longer than head. Subapical pin seta on Ant. IV with a short basal process, subapical organite small rod-shaped ( Fig. 5 ). AO on Ant. III normal, with 4 dorsal and 2 lateral sensilla ( Fig. 6 ), Ant. I with few thickened sensilla on ventral side and usually with 2–3 short basal microsensilla ( Fig. 7 ). Ant. II without clearly differentiated sensilla. Each side of a head with 6 large ocelli in a rather peculiar arrangement, ocelli A and D being located unusually far apart ( Fig. 8 ), ocelli G and H invisible. PAO elongate, about 1.8–2.0 as long as diameter of nearest ocellus. Labrum with 4/554 setae, apical edge with 4 indistinct low ridges and simple apical ciliation, central part of clypeal field with 5–7 setae ( Fig. 9 ). Maxillary outer lobe with a simple 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 seta on papillae subequal to guards, lateral process on papilla E finger-like; hypostomal papilla with H also subequal to h1/h2. Basomedial and basolateral fields of labium with 4 and 5 setae, respectively. Head with (4)5+5 postlabial setae along ventral line. Mandibles normal, with moderately strong teeth. Maxillae with a tridentate capitulum and 6 lamellae covered with fine denticles only, lamellae short, not projecting beyond tip of capitulum ( Fig. 10 ).

No ventral setae on thorax. Ventral tube with (2)3+3 frontal setae, usually with 4+4 lateral and 3–5 caudal setae with two longer ones in apical row ( Fig. 11 ). Retinaculum with 4+4 teeth and 2–5 setae. Manubrium with a variable number of ventral setae and usually 2+2 short apical ones; ventroapical thickening with blunt teeth ( Fig. 12 ). Dens with numerous ventral (anterior) setae and few dorsal (posterior) ones in the proximal third (up to 11–12, Fig. 13 ), ventroapical seta not prolonged ( Fig. 14 ). Mucro with four teeth, apical and subapical ones almost subequal, a lateral seta absent ( Figs 14–15 ). Tibiotarsi with 11 acuminate apical setae, Tib. 1–2 with 4(5)+4(5) setae along median line, basal part of foreleg usually with two outer setae, a third one rarely observed in the largest specimens. Unguis with a clear inner tooth and a pair of lateral ones in basal half; unguiculus about half as long as inner edge of unguis and also usually with a corner tooth.

Etymology. The new species is named in honor of Prof. Nils Adolf Eric Nordenskiöld and his voyage on the Vega along the northern coast of Eurasia (1878–1879). This name is given in our collection after the Russian- Swedish expedition «Tundra Ecology 94», dedicated to the 100th anniversary of this voyage. But even before that, it was known from the New Siberian Islands (V. Bulavintsev’s collection, 1985) and from the Magadan Region (1979, A. Fjellberg), but remained undescribed until now.

Affinities. Among the Palaearctic representatives of the tigrina group sensu Fjellberg (2007) [= fennica group sensu Potapov 2001) the new species is comparable only to D. intermedia ( Schött, 1902) sensu Fjellberg (2007) due to the fused last abdominal segments and long macrosetae. The latter species differs significantly in the number of dorsal macrosensilla: 76/55656, vs 33/ 21113 in D. nordenskioldi sp. nov.

This last character makes the new species distinguished from all representatives of the genus for which it is known. Among the Palaearctic species, a low number of dorsal macrosensilla (i.e. 32/22235 s) is shared only by D. blekeni ( Leinaas, 1980) as well as a recently described species from the closely related genus Vertagopus , V. glacialis Valle, 2025 (33/21124 s). A pair of cryophilic species of the family with a similarly low number of dorsal macrosensilla are also known from North America ( Fjellberg 2010), namely Myopia alaskana ( Christiansen & Bellinger, 1980) (22/11125 s) and D. olympica Fjellberg, 2010 (22/11135 s). None of these species are closely related and the reduction in the number of macrosensilla in them seems to have occurred independently.

Many forms have been described from various regions of the eastern Palearctic for which the sensory equipment of the terga is unknown. In particular, D. Japonica ( Yosii, 1939) , D. yukinomii ( Yosii, 1939) , D. spatiosa ( Uchida & Tamura, 1968) , D. husaini Yosii & Ashraf, 1965 , D. mazda ( Yosii, 1971) , and D. kosiana ( Bagnall, 1949) can be mentioned. The status of most of these species needs clarification ( Potapov 2001) and even their formal comparisons with the new species are very problematic, although we have failed to find any particular similarities between their existed descriptions and the new species.

Unfortunately, there are even more species in North America with unknown sensory chaetotaxy. Using the most comprehensive key to North American species ( Christiansen & Bellinger 1998), D. nordenskioldi sp. nov. could be identified as D. nigrifrons ( Folsom, 1937) on the basis of other characters. The latter species belongs to a different group, characterized by a bifurcate maxillary palp (see Fjellberg 1984).

The presence of only two setae in the distal row on the posterior surface of the ventral tube is also quite unusual for species of the tigrina group. This feature brings it closer only to D. taigicola ( Fjellberg, 1978) , which differs, however, in having separated last abdominal segments and short macrosetae.

Distribution and ecology. The species appears to be fairly widespread across the eastern Palearctic, inhabiting both coastal tundra and inland taiga regions ( Fig. 16 ).

Figures

FIGURES 16. Known locations of Desoria nordenskioldi sp. nov.

FIGURES 1–7. Desoria nordenskioldi sp. nov.: 1, general appearance and distribution of dorsal macro- and microsensilla; 2, dorsal chaetotaxy of head; 3, ibid., Th. II; 4, ibid., Abd. IV–VI; 5, antennal tip; 6, AO on Ant. III; 7, Ant. I, lateral view. Scales: 1–4, 0.1 mm, 5–7, 0.01 mm.

FIGURES 8–15. Desoria nordenskioldi sp. nov.: 8, PAO and ocelli; 9, labrum and maxillary outer lobe; 10, maxillary head; 11, VT, lateral view; 12, ventroapical part of manubrium; 13, dens; 14, distal part of dens and mucro, lateral view; 15, mucro, dorsal view. Scales: 9, 11, 13, 0.1 mm, 8, 10, 12, 14–15, 0.01 mm.