Thalassaphorura transbaikalica Gulgenova & Potapov 2023, sp. nov.

Thalassaphorura transbaikalica sp. nov. Figs 11–21, Table 1 Type material. Holotype: female, Russia, East Siberia, Buryatia, Vitim plateau, Eravna Basin, ~ 15 km northeast of Sosnovo-Ozerskoye, grass-wormwood meadow on salt licks, in soil, 26 August 2008. A. Gulgenova leg. Paratypes: 4 females and 4 males, same locality of the holotype, 26 August 2008. A. Gulgenova leg. Diagnosis. Pseudocellar formulae as 32/233/33343 dorsally and 11/000/01120 ventrally. Subcoxa 1 of legs 1–3 with 1, 2, 2 pso and 4, 4, 4 chaetae, respectively. Five guard papillae on the AIIIO. Head with 3+3 p-chaetae between the inner posterior pso. Th. 1 with 6+6 chaetae. Abd. 6 with one median a0 chaeta , AS present. Empodial appendage without basal lamella, 0.8–0.9 times as long as the inner edge of the claw. Th. 1–3 sterna with 1+1, 1+1, 1+1 chaetae, respectively. Ventral tube chaetae as 1+1/6+6/2+2. MVO absent. Description. Holotype (female) length 0.8 mm, length of paratypes: 0.6–0.7 mm (males) and 0.7–0.8 mm (females). Colour in alcohol white. Granulation more or less uniform, distinct. Body shape cylindrical, slightly broadened in the region of Abd. 3 and 4, with anal spines on papillae (Fig. 11). Anal spines 0.8 times as long as the inner edge of the hind claw. Antennae shorter than the head (ratio 0.8–0.9), their bases not marked. Ant. 1 with 9 chaetae, Ant. 2 with 13 chaetae (Fig. 13). Ant. 4 with the subapical organite with a globular apex (Fig. 12). Microsensillum on Ant. 4 above the second proximal row of chaetae. Ant. 3 microsensillum slightly below the AIIIO. Ant. 4 with 4 well-differentiated sensilla (3 dorsal-subapical and 1 internal-subapical). AIIIO with 5 guard chaetae, 5 papillae, 2 small sensory rods and 2 smooth, subequal and trilobed clubs (Figs 14, 15). Labral formula 4/142. Labial palp of AB type (Fig. 16). Labium with 7 proximal, 4 basomedial (E, F, G, f) and 5 basolateral (b, c, d, e, e’) chaetae, respectively; papillae A–E with a typical set of guard chaetae for Thalassaphorura, i.e. with 1, 4, 0, 3, and 2 chaetae, respectively. Maxillary palp simple, with 1 basal chaeta and 2 sublobal hairs. PAO with about 13–14 simple vesicles arranged in 2 rows along the axis of the organ (Fig. 17). Pso formula dorsally as 32/233/33343, ventrally: 11/000/01120 (Fig. 11). Subcoxa 1 of legs 1–3 with 1, 2, 2 pso respectively. Psx present on Abd. 1 sternum, near the base of the ventral tube. Dorsal chaetotaxy well differentiated into macro- and microchaetae (Fig. 11). Th. 2–3 with 1 microsensillum laterally, each. Head without chaeta d0. Head with 3+3 p-chaetae present between the two inner posterior pso. S-chaetae subcylindrical, distinguishable from ordinary chaetae, their formula as 11/011/222121 dorsally and 11/000/000100 ventrally. Th. 1 with 6+6 chaetae. Th. 2–3 and Abd. 1–3 with 3+3 axial chaetae, each. Abd. 4 with median chaeta m0.Abd. 5 with median chaeta a0 . Abd. 6 with one median chaeta a0 . Head with 4+4 ventral chaetae on each side of the mid-line. Th. 1, 2, 3 with 1+1; 1+1; 1+1 ventral chaetae, respectively. Subcoxae 1 of legs 1–3 with 4, 4, 4 chaetae, subcoxae 2 with 1, 4, 4 chaetae, coxae with 3, 9, 13, trochanters with 8, 9, 9, and femora with 14, 14, 12, respectively. Tibiotarsi 1–3 with 16 chaetae each (C: 1, B+M:8, A:7). Distal tibiotarsal whorl with 7 chaetae (Fig. 19). Ventral tube with 9+9 chaetae, as: 1+1/6+6/2+2 (Fig. 20). Furca reduced to a finely granulated area, with 4 small dental chaetae in 2 rows posteriorly. Chaetotaxy of the manubrial field with 4 chaetae in ma -row (2 middle small), 4 chaetae in mm -row (2 middle small) and 4 chaetae in mp -row (Fig. 18). Claws without denticle. Empodial appendage without basal lamella, 0.8–0.9 times shorter than the inner edge of the claw, with a short filament (Fig. 19). MVO absent. Genital plate with 12–13 chaetae in females and 24–26 in males. Each anal lateral valve with a0 and 2a1; upper valves with chaetae a0, 2a1, 2b1, 2b2, c0, 2c1, 2c2 (Fig. 21). Etymology. The new species was named after its type locality (Transbaikalia is the region to the east of Lake Baikal in Far Eastern Russia). Distribution and ecology. The species is only known from its type locality in the Vitim plateau (NE Buryatia). It inhabits saline meadows and cryo-arid steppes. Affinities. The genus Thalassaphorura is well revised. According to keys to the world species of the genus (Kaprus’ & Paśnik 2017; Sun et al. 2017) and morphological comparative tables of Sun & Wu (2013), Sun et al. (2017) and Kaprus’ & Paśnik (2017), the combination of the dorsal pso formula as 32/233/33343 and ventral formula as 11/000/01120 is shared by many species. Among them, only two, T. tibiotarsalis Sun, Chen & Deharveng, 2010 and T. thaibinhensis (Nguyen, 2001) have 7 chaetae in the distal whorl of the tibiotarsi, like T. transbaikalica sp. nov. The new species differs from T. tibiotarsalis by labial papillae of AB type (vs. ABC type in T. tibiotarsalis), S-chaetae formula dorsally (11/011/222121 vs. 11/011/222120), presence of anterior chaetae on the ventral tube, number of dorsal chaetae on Th. 1 (6+6 vs. 5+5), presence of a median chaeta on Abd. 5, number of chaetae on subcoxa 1 of legs 1–3 (4, 4, 4 vs. 3, 3, 3), and ratio of the empodial appendage and claw (0.8–0.9 vs. 0.5). The new species also has 1 pso on subcoxa 1 of leg 1 (T. tibiotarsalis has 2 pso), and differs in the number of vesicles in the PAO (13–14 vs. 17–18) (see also Table 1). Thalassaphorura thaibinhensis differs from T. transbaikalica sp. nov. by the ventral pso formula (10/000/01120 in T. thaibinhensis vs. 11/000/01120 in T. transbaikalica sp. nov.), number of pso on subcoxa 1 of leg 1 (2 vs. 1) and number of vesicles on the PAO (20 vs. 13–14). *Data based on the original descriptions of the species. In the edelweiss- Kobresia steppe of the Eravna basin we collected specimens slightly different from T. transbaikalica sp. nov. They have 15–22 vesicles on the PAO (vs. 13–14), a shorter empodial appendage (0,5 vs. 0,8–0.9 the length of claw), and the presence of unpaired chaetae on Abd. 6 ventrally, just in front of the anal spines. The status of this form calls for a further study.Published as part of Gulgenova, Ayuna & Potapov, Mikhail, 2023, Two new species of Onychiuridae (Collembola) from East Siberia (Russia), pp. 125-134 in Zootaxa 5336 (1) on pages 129-132, DOI: 10.11646/zootaxa.5336.1.6, http://zenodo.org/record/826864