Holotype (ISEA 6650): female, Russia, Chukotka Autonomous Okrug, Chaunskiy district, 2 kilometers from Apapelgino village, hill Akanotenmeem, in dry locality with Dryas sp., elev. 20 m, 69°48'40"N, 170°35'51"E, 24-VII-2018, coll. Makarov K. and Makarova O. Paratype (ISEA 6651): female, same data as holotype. The holotype and paratype are deposited in the collection of the Institute of Systematics and Evolution of Animals, Krakow, Poland (ISEA).

Nienna chukotka is characterized by 3 pairs of A-setae on the mesonotum, metanotum and tergite VIII, 3 A-setae on sternites I–VII, absence of P1a setae on tergites I–VI, 5 pairs of A-setae on tergites II–VII, absence of A2 on prosternum, presence of seta Pc on tergite VII and sternites VI–VII, and presence of additional d6 setae on head. Foretarsal sensillum a is broadened, very long, surpassing the base of sensillum e. Posterolateral pores (pl) present on tergite I, psl pores present on tergites VI and VII, asymmetrical spsm pores present on sternites IV–VII.

Head setae l3, sd4 and sd5 long, setiform, additional seta d6 present, length ratio of posterior setae d7:sd7:l5 as 2.4:2.5:1.0; frontal pore (fp) and a pair of clypeal (cp) pores present (Fig. 1A). Pseudoculus circular, with short posterior extension, PR = 12 (Fig. 1B). Sensilla of maxillary palps slender, pointed apically, equal in length (Fig. 1C). Labial palps with four-branched tuft of apical setae and broadened sensillum (Fig. 1D). Maxillary gland with small, indistinctly granulated calyx, short posterior filament and trilobed posterior dilation (Fig. 1E), CF = 6.0.

Foretarsus (Fig. 1J, H) without sensillum b’; t1 filiform, t3 small and globular; a broad, very long, evidently surpassing base of seta γ3, nearly reaching base of sensillum f; other sensilla parallel-sided. Sensillum b slightly longer than c. Sensillum d situated nearer to e than to c; a’ distal to level of t2 insertion. Length formula of sensilla: t3 < t1 < t2 < (c = e) < b < (g = a’ = c’) < (d = f) < a. Setae β1 and δ4 long and setiform, about twice as long as other δ-setae (Fig. 1H). Single pores situated near bases of sensilla t1 (Fig. 1J) and t3 (pore not visible on Fig. 1J because closed by sensillum e). Claw short, without inner tooth, empodial appendage short. BS = 0.4, TR = 2.7, EU = 0.3.

Figure 1. 

Nienna chukotka sp. nov. holotype. A Part of head B pseudoculus with setae sd4, sd5 and l3 C maxillary palpus D labial palpus E maxillary gland F female squama genitalis G exterior view of foretarsus H interior view of foretarsus I comb. Arrows show pores. Scale bars: 20 µm.

Formula of chaetotaxy given in Table 1. Setae on nota differing in length (Fig. 2A, B). Pronotal seta 1 1.6 times longer than seta 2 (Fig. 1A). Meso- and metanota with setae P1a and P2a setiform, lengths 7 and 5 μm, respectively; P2a situated nearly midway between P2 and P3 (Fig. 2A, B). Length ratio of mesonotal setae P1: P1a: P2 as 2.7: 1: 3.6. Meso- and metanota with sl and al pores (Fig. 2B). Pro-, meso- and metasterna without pores (Fig. 2E, F).

Accessory setae on tergites and sternites I–VII setiform, those of tergite VII significantly longer than those on I–VI. (Fig. 2C, D, G, H, K, L). Pores pl present on tergite I, psm on tergites I–VII, psl on tergites VI–VII, al on tergites II–VII (Fig. 2C, D, H).

Abdominal legs with 4, 2, 2 setae. Subapical and lateral apical setae on second and third pairs of abdominal legs nearly equal in length, 15 and 14 μm, respectively (Fig. 2J). Sternites I–III without pores (Fig. 2G). Sternites IV–VII with asymmetrical spsm pore, with short anterolateral lines and sternite VII with a connecting line on anterior part (Figs 2K, L).

Abdominal segment VIII with distinct striate band; tergite and sternite anteriorly with irregular small teeth (Figs 2 I, M). Pore psm without accompanying teeth. Posterior margin of sternite VIII and laterotergites smooth. Comb VIII with 9–10 small teeth (Fig. 1I). Seta 1a on tergite IX half the length of seta 1. Seta 2a on tergites IX and X shorter than other setae. Sternites IX–X with traces of striate band (Fig. 2N). Setae 1 and 2 on sternite IX of equal length, on sternite X seta 1 about half the length of seta 2 (Fig. 2N). Medial pore on dorsal lobe of segment XII and pair of sal pores on ventral lobe. Hind margin of dorsal lobe smooth, ventral lobe with fine serrations (Fig. 2O).

Female squama genitalis with short, pointed acrostyli (Fig. 1F).

Body measurements (2 females) (in μm): maximum body length 1004, head 115, pseudoculus 8, lever 3, posterior part of maxillary gland 12; pronotal setae 1 18, 2 11; mesonotal setae P1 19, P1a 7, P2 25, M 10, foretarsus 94–95, claw 30, empodial appendage 4.

Figure 2. 

Nienna chukotka sp. nov. holotype. A Part of pro- and mesonotum B part of metanotum C part of tergite I D part of tergite VI E anterior part of prosternum F anterior part of mesosternum G sternite I H part of tergite VII I part of tergite VIII J abdominal leg of segment II K sternite VI L sternite VII M sternite VIII N sternites IX–X O hind margin of sternite XII. Arrows show pores. Scale bars: 20 µm.

In the holotype, seta P4 is doubled asymmetrically on the mesonotum; in the paratype, seta A3 is absent symmetrically on tergite I and seta P2a is doubled on tergite VII.

The species name is taken from the general locality where the specimens were collected.

Nienna chukotka sp. nov. differs from N. parvula and N. quinghaiensis in the presence of seta Pc on tergite VII and sternites VI–VII (in N. quinghaiensis seta Pc is present on sternite VII only), the presence of 5 pairs of A-setae (4 pairs in the other two species) and P3a on tergite VII, the shape of the accessory setae on tergites and sternites I–VI (setiform in the new species, sensilliform in the other two species) and the shape of foretarsal sensilla a, c and e (in the other species sensillum a is shorter, reaching base of sensillum t2, sensilla c and e short and broad). The porotaxy of meso- and metanota and abdominal sternites also differs: Nienna chukotka has two pairs of sl and al pores on the meso- and metanota, and asymmetrical spsm pores on sternites IV–VII;], whereas N. parvula has a pair of sl pores on the meso- and metanota, and a simple spm pore on sternites VI–VII. Nienna quinghaiensis has al and l pores on the mesonotum, l pores on the metanotum, and an spm pore on sternite VII. The new species is more similar to N. parvula in possessing traces of a striate band on sternites IX–X and in the globular foretarsal sensillum t3. Nienna chukotka is characterized by the presence of pl on tergite I, which is the first report of posterolateral pores in Acerentomidae. Szeptycki (1988) previously described pl pores on Hesperentomon martynovae Szeptycki, 1988 (Hesperentomidae) collected in the Altai Mts. These pl pores have also been recorded in other Hesperentomon species: H. fopingense Bu, Shrubovych & Yin, 2011, H. nanshanensis Bu & Yin, 2007, H. xiningense Bu & Yin, 2007 distributed in China, and H. tianshanicum Martynova, 1970 (Shrubovych 2010).