Nienna chukotka sp. nov. (Protura, Acerentomidae, Nipponentominae) from the Arctic region, with a key to species of the genus.

A new species of Nienna was collected in the most northern part of the Palearctic, inside the Arctic Circle. In possessing seta Pc on tergite VII and sternites VI-VII and a very long foretarsal sensillum a, Nienna chukotka sp. nov. is more similar to Alaskaentomon species than to the other Nienna species distributed in southern Siberia and northern China. The new species differs from nearly all other members of Nipponentominae in possessing five anterior setae on tergite VII and in the presence of posterolateral pores on tergite I, as in members of Hesperentomon (Hesperentomidae). An identification key to Nienna species is provided. Julia Shrubovych.

Introduction

The proturan genus Szeptycki, 1988 was created for Szeptycki, 1988, described from the Altai mountains in southern Siberia (Szeptycki 1988). The genus differs from the 12 other genera of Yin, 1983 in possessing a small, indistinctly granulated calyx and a short posterior filament on the maxillary gland, and in the small, nearly globular foretarsal sensillum t3. A second species, Bu & Yin, 2008, was described from northern China. The diagnosis of the genus was recently updated (Galli et al. 2018). In the current paper, the description of a third species of is given. The type specimens, collected from the Arctic region, are the northernmost records for any . A key to the species of is given.

Materials and methods

specimens collected from western Chukotka in 2018 were extracted from soil samples with Berlese-Tullgren funnels into 95% ethanol. The specimens were mounted on glass slides in Faure’s medium (Dunger and Fiedler 1989).

The classification system of follows Szeptycki (2007). Terminology for body chaetotaxy and porotaxy follows Szeptycki (1988) and Shrubovych (2014); head seta designations follows Rusek et al. (2012).

Abbreviations

abdominal segments,

thoracic segments,

anterior setae,

posterior setae,

frontal,

clypeal,

anterolateral,

sublateral,

sternal anterolateral,

posterosubmedial,

posterosublateral,

posterolateral,

sternal posteromedial,

sternal posterosubmedial cuticular pore.

Results

The genus is characterized by three pairs of A-setae on the mesonotum and metanotum, small, indistinctly granulated appendices on the calyx and a short posterior filament on the maxillary gland. The foretarsal sensillum t1 is filiform, sensillum t3 is small and globular (lanceolate in Bu &Yin, 2008), the position of sensillum d is close to the base of e, and seta β1 is setiform. Sensillum a’ is distal to the base of t2. Sensillum b’ is missing. The genus is similar to twelve other genera from the subfamily in having abdominal legs with 2 nearly equal setae, 5 pairs of A-setae on tergites II–VI (except for Nosek, 1977 and Bu & Yin, 2007) and by the posterior position of seta P3 on abdominal tergites II–VI (except for Nosek, 1977) (Bu and Yin 2007; Bu et. al. 2013; Galli et al. 2018; Nosek 1977, 1981; Shrubovych 2009, 2011, 2014; Shrubovych and Smykla 2012; Shrubovych et al. 2012; Shrubovych et al. 2014a, b, c).

sp. nov.

41411DC6-9440-55FA-B1C5-3D0FA594C3F5

http://zoobank.org/2FEE913F-CC4C-445A-869E-F25B7267F644

Figs 1 , 2 , Table 1

Figure 1.

sp. nov. holotype. A Part of head B pseudoculus with setae sd4, sd5 and l3C 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.

Figure 2.

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.

Table 1.

Body chaetotaxy of sp. nov.

	Dorsal		Ventral
Segment	Formula	Setal composition	Formula	Setal composition
Th. I	4	1, 2	(2+4)/6	A1, M1, 2,
				P1, 2, 3
Th. II	8/16	A2, 3, 4, M	(5+2)/4	Ac, 2, 3, M
		P1, 1a, 2, 2a, 3, 3a, 4, 5		P1, 3
Th. III	8/16	A2, 3, 4, M	(7+2)/4	Ac, 2, 3, 4, M
		P1, 1a, 2, 2a, 3, 3a, 4, 5		P1, 3
Abd. I	8(6)/10	A1, 2, (3), 5	3/4	Ac, 2
		P1, 2, 2a, 3, 4		P1, 1a
Abd. II-III	10/14	A1, 2, 3, 4, 5	3/5	Ac, 2
		P1, 2, 2a, 3, 4, 4a, 5		Pc, 1a, 2
Abd. IV-V	10/14	A1, 2, 3, 4, 5	3/8	Ac, 2
		P1, 2, 2a, 3, 4, 4a, 5		P1, 1a, 2, 3
Abd. VI	10/14	A1, 2, 3, 4, 5	3/9	Ac, 2
		P1, 2, 2a, 3, 4, 4a, 5		Pc, 1, 1a, 2, 3
Abd. VII	10/19	A1, 2, 3, 4, 5	3/9	Ac, 2
		Pc, 1, 1a, 2, 2a, 3, 3a, 4, 4a, 5		Pc, 1, 1a, 2, 3
Abd. VIII	6/15	A1, 4, 5	4/2	1, 2
		Pc, 2, 2a, 3, 3a, 4, 4a, 5		P1a
Abd. IX	12	1, 1a, 2, 2a, 3, 4	4	1, 2
Abd. X	10	1, 2, 2a, 3, 4	4	1, 2
Abd. XI	6	1, 3, 4	6
Abd. XII	9		6

(3) – setae A3 absent in paratype. Tergite I with 6 A-setae.

Material examined.

Holotype (ISEA 6650): female, Russia, Chukotka Autonomous Okrug, Chaunskiy district, 2 kilometers from Apapelgino village, hill Akanotenmeem, in dry locality with sp., elev. 20 m, , 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).

Diagnosis.

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 () present on tergite I, pores present on tergites VI and VII, asymmetrical pores present on sternites IV–VII.

Description.

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 () and a pair of clypeal () 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.

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 and 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 present on tergite I, on tergites I–VII, on tergites VI–VII, 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 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 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 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.

Chaetal variability.

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.

Etymology.

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

Remarks.

sp. nov. differs from and in the presence of seta Pc on tergite VII and sternites VI–VII (in 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: has two pairs of and pores on the meso- and metanota, and asymmetrical pores on sternites IV–VII;], whereas has a pair of pores on the meso- and metanota, and a simple pore on sternites VI–VII. has and l pores on the mesonotum, l pores on the metanotum, and an pore on sternite VII. The new species is more similar to in possessing traces of a striate band on sternites IX–X and in the globular foretarsal sensillum t3. is characterized by the presence of on tergite I, which is the first report of posterolateral pores in . Szeptycki (1988) previously described pores on Szeptycki, 1988 () collected in the Altai Mts. These pores have also been recorded in other species: Bu, Shrubovych & Yin, 2011, Bu & Yin, 2007, Bu & Yin, 2007 distributed in China, and Martynova, 1970 (Shrubovych 2010).

Discussion

The foretarsus of sp. nov. has a very long sensillum a, surpassing the base of sensillum e, and filiform foretarsal sensillum t1, characters shared with two species of (, ). These two species possess seta Pc on tergite VII and sternites VI–VII. spp. differ from sp. nov. in having two pairs of A-setae on the meso- and metanota and large granulated appendices on the calyx of the maxillary gland (Shrubovych et al. 2014c). In notal chaetotaxy (three pairs of A-setae) and the filiform sensillum t1, the genus is similar to the genera Yin, 1980, Szeptycki, 1988, Imadaté, 1980 and Rusek, 1974. However, differs from all of them in possessing small, indistinctly granulated appendices on the calyx of the maxillary gland and in the small, nearly globular foretarsal sensillum t3 (Shrubovych et al. 2014a). The new species differs from nearly all species of in possessing a pair of A1 setae on tergite VII (five pairs of A-setae), while nearly all other nipponentomines have four pairs of A-setae (except Nosek, 1977 from Alaska, which also has 5 pairs of A-setae). Therefore, sp. nov. from Chukotka is more similar in body chaetotaxy and in foretarsal sensilla pattern to members of other genera distributed in Alaska than to the other species distributed in more southern regions of the Palearctic. This peculiarity could be an effect of subsequent allopatric speciation resulting from successive closings of the Bering Strait and cooling of the Arctic Ocean during the Pliocene-Pleistocene. Another interesting fact is that species recorded on the northern edge of proturan distribution (only a few species are known from the Arctic region) possess a larger number of setae on the body than species with a more southern distribution.

1	Foretarsal sensillum a very long, surpassing base of sensillum e, tergite VII with 5 pairs of A-setae and with Pc, P3a present, sternites VI–VII with Pc	Nienna chukotka sp. nov.
–	Foretarsal sensillum a short, nearly reaching base of sensillum t2, tergite VII with 4 pairs of A-setae and without Pc, P3a absent, sternite VI without Pc, sternite VII with or without Pc	2
2	Foretarsal sensilla b and c nearly equal in length, seta δ4 setiform, sternite VII without Pc	N. parvula Szeptycki, 1988
–	Foretarsal sensillum c half the length of b, seta δ4 sensilliform, sternite VII with Pc	N. quinghaiensis Bu & Yin, 2008