Holotype male, two female paratypes on slides – China, Heilongjiang, Shuangyashan, Baoqing, Qinglongshan (46.1504°N, 131.9591°E), 14.Aug.2010, litter and soil under Betula costata Trautv., Berlese extraction, Wu Donghui et al. leg. (LD-10-344).

Pso formulae as 32/033/33343 dorsally and 11/000/01(0)010 ventrally. Subcoxae 1 of legs I, II and III with 1, 1 and 1 pso respectively. Psx formula as 00/000/100001^m ventrally. PAO with 14–17 compound vesicles. Th. I–III sterna with 0+0, 1+1, 1+1 chaetae respectively. Ventral tube with 1+1 basal chaetae. Subcoxae 1 of legs I, II and III with 5, 7 and 6 chaetae respectively.

Body length: females 1.30–1.37 mm, male holotype 1.08 mm. Shape of body typical of the genus: cylindrical with strong anal spines on papillae. Color in alcohol white.

Pso formulae: 32/033/33343 dorsally and 11/000/01(0)010 ventrally (Figs 1A, B, C). Subcoxae 1 of legs I–III with 1 pso each. Parapseudocellar formulae: 00/000/100001^m ventrally, dorsally psx absent (Figs 1A, B, C). Pseudopore formulae: 00/011/11110 dorsally and 00/111/001^m1^m 0 ventrally (Figs 1A, B, C).

Head. Antennae short, 1.2 times as long as head. Length ratio of antennal segments I : II : III : IV = 1 : 1.5 : 1.5 : 2. Subapical organite on Ant. IV with globular apex; basolateral ms above the second proximal row of chaetae. Ant. III sensory organ consisting of 5 papillae, 5 guard chaetae, 2 small sensory rods, 2 granulated sensory clubs and a later ms (Fig. 2A). Ant. II with 15 chaetae. Ant. I with 10 chaetae. Antennal base weakly marked. PAO with 14–17 compound vesicles arranged in two rows along axis of organ (Fig. 2B). Dorsal cephalic chaeta d0 present. 4+4 p-chaetae between posterior a-pso on head, p1 in line with others (Fig. 1A). Mandible with strong molar plate and 4 apical teeth. Maxilla bearing 3 teeth and 6 lamellae. Maxillary palp simple with 1 basal chaeta and 2 sublobal hairs. Labral chaetal formula 4/342. Labium with 6 proximal, 4 basomedian (E, F, G and f), and 5 basolateral chaetae (b, c, d, e, e’) (Fig. 1B); labial palp of AC type, labial papillae A–E with 1, 4, 0, 3, and 3 guard chaetae respectively. 5+5 postlabial chaetae along ventral groove (Fig. 1B).

Body chaetotaxy. S-chaetae formulae as 11/022/222120 dorsally and 11/000/000100 ventrally (Figs 1A, B, C). Tiny and blunt ms, present on Th. II–III dorsal-laterally (Fig. 1A). Dorsal ordinary chaetae differentiated, Sp : m1 : p1 ratio on Abd. V = 1 : 0.8 : 2.5 (Fig. 1A). Th. I tergum with 9–12 chaetae. Th. II–III terga with 5+5 and Abd. I–III terga with 3–4+3–4 chaetae on both side of axial line respectively and no unpaired axial chaetae (Fig. 1A). On each other abdominal terga from Abd. IV to Abd. VI tergum axial chaetae m0 present (Fig. 1A). Th. I–III sterna with 0+0, 1+1, 1+1 chaetae between legs respectively.

Appendages. Subcoxae 1 of legs I, II and III with 5, 7 and 6 chaetae, subcoxae 2 with 1, 5 and 5 chaetae respectively. Coxae of legs I, II and III with 4, 11 and 14 chaetae, trochanters with 10 chaetae each and femora with 15, 17 and 17 chaetae. Tibiotarsi of legs I, II and III with 22 (3, 8, 11), 20 (1, 8, 11) and 21 (2, 8, 11) chaetae (Fig. 2C). Unguis without teeth. Unguiculus slender and pointed, 0.8–0.9 times as long as inner edge of unguis, without inner basal lamella (Fig. 2C). Ventral tube with 6–9+6–9 distal chaetae and 1+1 basal chaetae, without anterior chaetae (Fig. 1C). Furca reduced to cuticular fold with 4 small dental chaetae posteriorly and two manubrial rows of chaetae (Fig. 2B)

Genital plate with 16–25 chaetae in females (Fig. 2D), 26 in male. Male ventral organ absent. Anal valves with numerous acuminate chaetae; each lateral valve with a0, 2a1 and 2a2; upper valve with chaetae a0, 2a1, 2b1, 2b2, c0, 2c1 and 2c2 (Fig. 1C). Anal spines set on distinct papillae, as long as inner edge of hind unguis (Fig. 1A).

Named for the name of mountain (Qinglongshan, and -shan means mountain in Chinese) where the species was found.

Until now, there are four known species belonging to the genus Bionychiurus: Bionychiurus changbaiensis Sun & Wu, 2012 from China, Bionychiurus normalis (Gisin, 1949) from Europe, Bionychiurus oblongatus (Lee & Park, 1986), and Bionychiurus yongyeonensis (Yosii, 1966) from South Korea (Bellinger et al. 1996–2014; Sun and Wu 2012). The new species can be easily distinguished from all the above mentioned congeners by the absence of pso on Th. I tergum (present in other species) and fewer number of vesicles in PAO (more than 17 in other species).

Holotype male, 7 female and 6 male paratypes on slides – China, Heilongjiang, Shuangyashan, Baoqing, Qinglongshan (46.1504°N, 131.9591°E), 14.Aug.2010, litter and soil under Betula costata Trautv., Berlese extraction, Wu Donghui et al. leg. (LD-10-444, LD-10-445); 12 female and 3 male paratypes on slides – China, Heilongjiang, Jiamusi, Tongjiang, Jiejinshan (47.9185°N, 132.8503°E), 7.Aug.2010, litter and soil under Quercus mongolica Fisch. ex Ledeb., Berlese extraction, Wu Donghui et al. leg. (LD-10-484, LD-10-485, LD-10-486, LD-10-488).

Diagnosis. Pso formulae as 32/133/33352 dorsally and 3/011/31120 ventrally. Psx formula as 0/000/111001+1^m ventrally.. Ratio of AS/unguis as 0.6. Unguiculus without inner basal lamella. Male ventral organ absent.

Body length: females 1.6–1.8 mm, males 1.4–1.6 mm; holotype 1.6 mm. Shape of body typical of the genus: cylindrical with anal spines on papillae, Abd. III–IV more or less broadened. Color in alcohol white.

Pso formulae: 32/133/33352 dorsally and 3/011/31120 ventrally (Figs 3A, H, 4A). Subcoxae 1 of legs I–III with 2 pso each. Parapseudocellar formulae: 0/000/111001+1^m ventrally, dorsally psx absent (Figs 3A, H, 4A). Pseudopore formulae as 00/011/11110 dorsally and 00/111/0001^m00 ventrally (Figs 3A, H, 4A).

Head. Antennae short, as long as head. Length ratio of antennal segments I : II : III : IV = 1 : 1.5 : 1.5 : 2.0. Subapical organite on Ant. IV with globular apex (Fig. 3C); invaginated apical bulb present (Fig. 3E); basolateral ms above the first proximal row of chaetae (Fig. 3C). Ant. III sensory organ composed of 5 papillae, 5 guard chaetae, 2 small rods, and 2 smooth sensory clubs (Fig. 3D); lateral ms just behind sensory organ (Fig. 3C). Ant. II with 14 chaetae. Ant. I with 8 chaetae. Antennal base well marked. PAO with 14–16 compound vesicles arranged in two rows along axis of organ (Fig. 3B). Dorsal cephalic chaeta d0 present. 3+3 p-chaetae between two inner posterior pso on head, p1 anterior to others (Fig. 3A). Mandible with strong molar plate and 4 apical teeth. Maxilla bearing 3 teeth and 6 lamellae. Maxillary palp simple with 1 basal chaeta and 2 sublobal hairs. Labral chaetae 4/142. Labium with 6 proximal, 4 basomedian (E, F, G, and f) and 5 basolateral (b, c, d, e, e’) chaetae (Fig. 4A). Labial palp of AB type, labial papillae A–E with 1, 4, 0, 3 and 3 guard chaetae respectively (Fig. 3F). Postlabial chaetae 4–5+4–5 along ventral groove (Fig. 4A).

Body chaetotaxy. S-chaetae not distinguishable from ordinary chaetae. Tiny and blunt ms, present on Th. II and III dorso-laterally (Fig. 3A). Dorsal ordinary chaetae poorly differentiated, usually coarse and short. Th. I tergum with 8–14+8–14 chaetae. Th. II–Abd. III terga with 4–5+4–5 chaetae along axial line respectively, usually with asymmetrical chaetae (Fig. 3A). Abd. IV tergum with p0 chaeta; Abd. V tergum without axial chaeta; Abd. VI tergum with m0 chaeta (Fig. 3A). Th. I–III sterna without chaetae between legs.

Appendages. Subcoxae 1 of legs I–III with 5, 5 and 5 chaetae, subcoxae 2 with 1, 4 and 4 chaetae respectively. Coxae of legs I, II and III with 3, 9–11 and 9–12 chaetae, trochanters with 9 chaetae each and femora with 15, 16 and 16 chaetae. Tibiotarsi of legs I, II and III with 17 (9, 7, 1), 18 (9, 7, 2) and 17 (9, 7, 1) chaetae, M-chaeta absent. Unguis without teeth. Unguiculus slender and pointed, 0.8 times as long as inner edge of unguis, without inner basal lamella (Fig. 3G). Ventral tube with 6–8+6–8 distal chaetae, without anterior or basal chaetae. Furca reduced to finely granulated area, with 4 small dental chaetae in one row posteriorly; three manubrial rows of chaetae present (Figs 3H, 4C).

Genital plate with 17–23 chaetae in females, 40–63 chaetae in males. Male ventral organ absent. Anal valves with numerous acuminate chaetae; each lateral valve with chaetae a0 and 2a1; upper valve with chaetae a0, 2b1, 2b2, c0, 2c1 and 2c2 (Fig. 4B). Anal spines set on distinct papillae, 0.6 times as long as inner edge of hind unguis (Fig. 3A).

Named for the province of the type locality.

The new specie shares the same dorsal pso formula from head to Abd. IV (32/133/3335), ventral pso formula from head to Abd. I (3/011/3) and number of pso on subcoxae 1 of legs I–III (2, 2, 2 respectively) with a number of the known European species, i.e. Onychiurus ambulans (Linnaeus, 1758) sensu Pomorski, 1998, Onychiurus arans Gisin, 1952, Onychiurus circulans Gisin, 1952, Onychiurus insinuans Gisin, 1952, Onychiurus subcirculans Gisin, 1962, and Onychiurus sublegans Gisin, 1960, but it can be distinguished easily from all these species as having only 2 pso on each side of Abd. V (3 or 4 in other species) and no male ventral organ (present in other species).