Holotype. ♀ on slide, China, Zhejiang Province, Hangzhou City, Xihu District, Jiuxi Bus Station, 30°11'25″N, 120°06'47″E, 29 m asl, sample number 1183, collected by Y-T Ma, 6-VII-2018, from leaf litter, deposited in NTU. Paratypes. 4♀♀ on slides, same data as holotype.

3♀♀ on slides, China, Zhejiang Province, Hangzhou City, Linan District, Gate of Tianmu Mountain, 30°18'31″N, 119°26'44″E, 275 m asl, sample number 1181, collected by Y-T Ma, 14-VII-2018, from leaf litter; 3♀♀ on slides, CHINA, Jiangxi Province, Yichun City, Tonggu County, Tonggu Park, 28°31'54″N, 114°22'36″E, 239 m asl, sample number 1235, collected by Y-T Ma, 14-XI-2020, from leaf litter. All deposited in NTU.

Size. Body length up to 2.31 mm.

Coloration. Ground colour pale white to pale yellow. Eye patches dark blue. Antennae gradually darker from Ant. I to Ant. IV. Brown to blue-violet pigment present on head anteriorly and laterally, thorax laterally and abdomen entirely, legs, ventral tube and basal manubrium. A narrow midline irregular longitudinal stripe present on midline from Th. II to Abd. I or II (Figs 2–6).

Head. Antenna 0.67–1.00 times body length; antennal segment ratio I: II: III: IV = 1: 1.23–1.50: 1.00–1.29: 1.43–2.43. Apical bulb of Ant. IV bilobed (Fig. 7). Ant. III organ with two distal rod-like chaetae ventrally (Fig. 8). Ant. II with four distal rod-like chaetae ventrally (Fig. 9). Eyes 8 + 8, G and H smaller than others; interocular chaetae with p, r, and t mes. Dorsal cephalic chaetotaxy with four antennal (An1, An2, An3a1, An3), five median (M1, M2, M3i, M3, M4) and eight sutural (S0, S1, S2, S3, S4, S4i, S5i, S5) mac (Fig. 10). Labral chaetae as 4/5, 5, 4, all smooth; labral papillae absent (Fig. 11). Lateral process (l.p.) of labial papilla E differentiated, as thick as normal chaeta, with tip not reaching apex of papilla E (Fig. 12). Chaetal formula of labial base as MRel₁L₂, chaetae e and l₁ smooth, others ciliate, R/M as 0.40–0.67 (Fig. 13). Basal chaeta of maxillary outer lobe thin, subequal to apical one; sublobal plate with three smooth chaeta-like processes (Fig. 14).

Thorax.Th. II with four medio-medial (m1, m2, m2i, m2i2), three medio-sublateral (m4, m4i, m4p), 23–32 posterior mac, one ms and two sens (ms antero-internal to sens). Th. III with 30–43 mac and two sens (Fig. 15). Pseudopores on coxa I–III as 2, 3, 2, respectively; coxal macrochaetal formula as 4 (rarely 3)/4+2, 3/4+2 (Figs 16–18). Trochanteral organ with 37–68 smooth spiny chaetae (Fig. 19). Tenent hair capitate and almost subequal to inner edge of unguis in length. Unguis with four inner teeth and distal one very faint, basal pair located at 0.40–0.49 distance from base of inner edge of unguis, distal unpaired teeth at 0.67–0.73 and 0.83–0.88 distance from base, respectively; unguiculus lanceolate, outer edge slightly serrate (Fig. 20).

Abdomen. Range of Abd. IV length as 5.33–6.90 times as dorsal axial length of Abd. III. Abd. I usually with 11 (a1–3, a5, m2–4, m2i, m4i, m4p, a1a and a1 rarely absent), ms antero-external to sens. Abd. II with six (a2, a3, m3, m3e, m3ea, m3ep) central, one (m5) lateral mac and two sens. Abd. III with two (a2, m3) central and four (am6, pm6, m7a, p6) lateral mac, one ms and two sens (Fig. 21). Abd. IV with two normal sens and about half length of elongate sens; anteriorly with 7–12 mac arranged in irregular transverse row, posteriorly with six central mac (A4, A5, A6, B4, B5, B6), laterally with 17–24 mac (Fig. 22). Abd. V with three sens, middle one posterior to m3 (Fig. 23). Anterior face of ventral tube with 31–42 ciliate chaetae, 3+3 of them as mac, line connecting proximal (Pr) and external-distal (Ed) mac oblique to median furrow (Fig. 24); posterior face with numerous ciliate chaetae and 4–5 smooth chaetae apically (Fig. 25); lateral flap with 7–11 smooth and 6–10 ciliate chaetae (Fig. 26). Manubrial plate dorsally with 8–13 ciliate chaetae and three pseudopores (Fig. 27); ventrally with 21–34 ciliate chaetae on each side (Fig. 28). Dens with 28–39 smooth inner spines (Fig. 29). Mucro bidentate with subapical tooth larger than apical one; tip of basal spine reaching apex of subapical tooth; distal smooth section of dens almost equal to mucro in length (Fig. 30).

Named after its similar species H. zhangi (pseudo+zhangi).

In the leaf litter

The new species is characterised by a narrow irregular longitudinal stripe on the body, smooth chaetae e and l₁ on the labial base and ms antero-external to the sens on Abd. I. It is similar to H. acutus Jing & Ma, 2022, H. mediofascia Shi, Pan & Bai, 2009, H. yangdangensis Pan, 2015 and H. zhangi Pan & Shi, 2012 in colour pattern, but can be separated from them by the smooth chaetae on the labial base, the relative position of ms on Abd. I and other characters. It is also similar to H. phjongjangica Szeptycki, 1973, H. sichuanensis Jia, Zhang, Zhao & Jordana, 2010 and H. sinensis Denis, 1929 in body chaetotaxy, but there are some differences between them in colour pattern, coxal macrochaetal formula and other characters (Table 1).

Holotype. ♀ on slide, China, Guizhou Province, Liupanshui City, Pan County, Laochang Town, Shangkanzhe Village, 25°39'34″N, 104°48'28″E, 1677 m asl, sample number 1176, collected by H-D Tan, 6-II-2017, from bamboo litter, deposited in NTU. Paratype. ♀ on slide, same data as holotype.

Size. Body length up to 2.38 mm.

Coloration. Ground colour pale white or yellow. Ant. I pale yellow and Ant. II–IV blue. Eye patches dark blue and a transverse blue stripe between eye patches. Blue pigment present on dorsal head and Th. II–III laterally, legs, ventral tube and Abd. V. Abd. II–III with an irregular transverse blue stripe, respectively. Abd. IV with an irregular transverse blue stripe medially and a narrow blue stripe posteriorly (Figs 31, 32).

Head. Antenna 0.64–0. 69 times body length; antennal segment ratio I: II: III: IV = 1: 1.20–1.27: 1.05–1.09: 1.92–2.27. Apical bulb of Ant. IV bilobed (Fig. 33). Ant. III organ with two distal rod-like chaetae ventrally (Fig. 34). Ant. II with four distal rod-like chaetae ventrally (Fig. 35). Eyes 8 + 8, G and H smaller than others; interocular chaetae with p, r, and t mes. Dorsal cephalic chaetotaxy with four antennal (An1, An2, An3a1, An3), five median (M1, M2, M3i, M3, M4) and nine sutural (S0, S1, S2, S3, S3p, S4, S4i, S5i, S5) mac (Fig. 36). Labral chaetae as 4/5, 5, 4, all smooth; labral papillae not seen (Fig. 37). Lateral process (l.p.) of labial papilla E differentiated, as thick as normal chaeta, with tip almost reaching apex of papilla E (Fig. 38). Chaetal formula of labial base as MReL₁L₂, chaeta e smooth, others ciliate, R/M as 0.50–0.58 (Fig. 39). Basal chaeta of maxillary outer lobe thin, subequal to apical one; sublobal plate with three smooth chaeta-like processes (Fig. 40).

Thorax.Th. II with four medio-medial (m1, m2, m2i, m2i2), three medio-sublateral (m4, m4i, m4p), 36–38 posterior mac, one ms and two sens (ms antero-internal to sens). Th. III with 47 mac and two sens (Fig. 41). Trochanteral organ with 53 smooth spiny chaetae (Fig. 42). Tenent hair capitate and almost subequal to inner edge of unguis in length. Unguis with four inner teeth and distal one very faint, basal pair located at 0.43–0.49 distance from base of inner edge of unguis, distal unpaired teeth at 0.65–0.70 and 0.87 distance from base, respectively; unguiculus lanceolate, outer edge slightly serrate (Fig. 43).

Abdomen. Range of Abd. IV length as 6.43–7.50 times as dorsal axial length of Abd. III. Abd. I with 11 (a1a, a1–3, a5, m2–4, m2i, m4i, m4p), ms antero-external to sens. Abd. II with six (a2, a3, m3, m3e, m3ea, m3ep) central, one (m5) lateral mac and two sens. Abd. III with two (a2, m3) central and four (am6, pm6, m7a, p6) lateral mac, one ms and two sens (Fig. 44). Abd. IV with two normal sens and about half length of elongate sens; anteriorly with 12–13 mac arranged in irregular transverse row, posteriorly with nine central mac (A4–6, B4–6, Ae5–7), laterally with 21–23 mac (Fig. 45). Abd. V with three sens, middle one posterior to m3 (Fig. 46). Anterior face of ventral tube with 30 ciliate chaetae, 3+3 of them as mac, line connecting proximal (Pr) and external-distal (Ed) mac oblique to median furrow (Fig. 47); posterior face with numerous ciliate chaetae and six smooth chaetae apically (Fig. 48); lateral flap not seen entirely (Fig. 49). Manubrial plate dorsally with 13–14 ciliate chaetae and three pseudopores (Fig. 50); ventrally with 36–37 ciliate chaetae on each side (Fig. 51). Dens with 54–57 smooth inner spines (Fig. 52). Mucro bidentate with subapical tooth larger than apical one; tip of basal spine reaching apex of subapical tooth; distal smooth section of dens almost equal to mucro in length (Fig. 53).

Named after its locality: Guizhou Province, which is abbreviated as Qian.

In the leaf litter of bamboo.

The new species is characterised by its colour pattern on the antennae and nine sutural mac on the head. Among 77 known species of the genus, 51 species have eight sutural mac and only nine species have nine sutural mac. There are some significant differences among them, such as colour pattern on the antennae and thorax, mac on Abd. III–IV and other characters, which are listed in Table 2.

Holotype. ♀ on slide, China, Shaanxi Province, Xian City, Zhouzhi County, Cuifeng Town, Qingshan Park, 34°04'49″N, 108°01'58″E, 901 m asl, sample number 1109, collected by Y-T Ma, 17-VII-2012, from leaf litter, deposited in NTU. Paratypes. 4♀♀ on slides, same data as holotype.

Size. Body length up to 1.65 mm.

Colouration. Ground colour pale yellow in ethanol. Ant. IV and distal part of Ant. I–III blue pigment. Eyepatches dark blue. An irregular blue stripe present from eyepatch to Th. III laterally and from Th. II to Abd. III sublaterally, respectively. Posterior part of Abd. III with a transverse irregular blue stripe. Abd. IV with two irregular transverse stripes, one located medially and other posteriorly. Abd. V with a pair of blue spots. Legs with scattered pigment (Figs 54, 55).

Head. Antenna 0.47–0.55 times body length; antennal segment ratio I: II: III: IV = 1: 1.70–2.00: 1.50–1.88: 2.43–2.75. Apical bulb of Ant. IV bilobed (Fig. 56). Eyes 8 + 8, G and H smaller than others, interocular chaetae with p, r, and t mes. Dorsal cephalic chaetotaxy with five antennal (An1, An2a, An2, An3a1, An3), four median (M1, M2, M3, M4) and eight sutural (S0, S1, S2, S3, S4, S4i, S5i, S5) mac (Fig. 57). Labral chaetae 4/5, 5, 4, all slender; prelabral chaetae ciliate, other smooth, four labral papillae with one minute denticle each (Fig. 58). Lateral process (l.p.) of labial papilla E differentiated, as thick as normal chaeta, with tip exceeding apex of papilla E (Fig. 59). Chaetal formula of labial base as MREL₁L₂, M rarely duplicate, all ciliate; R 0.56–0.71 times length of M (Fig. 60).

Thorax.Th. II usually with four medio-medial (m1, m2, m2i, m2i2 rarely absent), four medio-sublateral (m4, m4i, m4p, m4pi, m4i2 rarely present), 23–27 (p6 sometimes absent) posterior mac, one ms and two sens (ms antero-external to sens). Th. III with 29–33 mac and two sens (Fig. 61). Trochanteral organ with 21–27 smooth spiny chaetae (Fig. 62). Tenent hair capitate and longer than inner edge of unguis in length. Unguis with four inner teeth. Unguiculus acuminate and outer edge slightly serrate (Fig. 63).

Abdomen. Range of Abd. IV length as 4.03–5.50 times dorsal axial length of Abd. III. Abd. I with 10–11 (a1, a1a, a2–3, m2–4, m2i, m4i, m4p, a5, a1a sometimes absent) mac, ms antero-external to sens. Abd. II with six (a2, a3, m3, m3e, m3ea, m3ep) central, one (m5) lateral mac and two sens. Abd. III with two (a2, a3) central, and four (am6, pm6, m7a, p6) lateral mac, one ms and two sens (Fig. 64). Abd. IV with two normal length sens; centrally with eight mac, laterally 13–16 mac (Fig. 65). Abd. V with three sens, middle one posterior to m3 (Fig. 66). Anterior face of ventral tube with some ciliate chaetae, 3+3 of them as mac, line connecting proximal (Pr) and external-distal (Ed) mac oblique to median furrow (Fig. 67); posterior face and lateral flap not clearly seen. Manubrial plaque dorsally with about five ciliate chaetae and three pseudopores (Fig. 68); ventrally with 11–13 ciliate chaetae (Fig. 69). Distal smooth part of dens about 2.33 times as long as mucro. Mucro bidentate with subapical tooth subequal to apical one; tip of basal spine reaching apex of subapical tooth (Fig. 70).

Named after its locality: Shaanxi Province.

In the leaf litter.

The new species is characterised by its colour pattern, one minute denticle on each labral papilla, and the tip of the lateral process (l.p.) of the labial papilla E exceeding the apex of the papilla E. It is very similar to E. aino (Matsumara & Ishida, 1931) in colour pattern, macrochaetotaxy of Abd. III–IV and other characters, but there are some differences between them, such as chaetotaxy on Abd. I, II and IV (Table 3).

5♀♀ on slides, China, Jiangsu Province, Nantong City, Intersection of Tongning Highway and Pingning Road, 32°04'21″N, 120°50'19″E, sample number 1249, collected by Y-T Ma, 1-IX-2022, in the leaf litter of Salix babylonica.

Size. Body length up to 1.81 mm.

Coloration. Ground colour pale white to pale yellow. Eye patches dark blue. A little brown pigment present on antennae and Abd. V (Figs 71, 72).

Head. Antenna 0.70–1.03 times body length; antennal segment ratio I: II: III: IV = 1: 1.10–1.34: 1.10–1.40: 1.60–1.83. Apical bulb of Ant. IV simple (Fig. 73). Eyes 8 + 8, G and H smaller than others; interocular chaetae with p, r, and t mes. Dorsal cephalic chaetotaxy with five antennal (An1, An2a, An2, An3a1, An3), two median (M2, M4), and three sutural (S2, S3, S6) mac (Fig. 74). Labral chaetae as 2/5, 5, 4, prelabral chaetae ciliate, other smooth; labral margin with four papillae (Fig. 75). Basal chaeta of maxillary outer lobe thin, subequal to apical one; sublobal plate with three smooth chaeta-like processes (Fig. 76). Lateral process (l.p.) of labial papilla E differentiated, as thick as normal chaeta, with tip not reaching apex of papilla E (Fig. 77). Labium with ABCDF chaetae, all smooth, chaeta F apically blunt; chaetae of labial base as MRL₁L₂, all ciliate (Fig. 78).

Thorax.Th. II with one medio-medial (m2), three (p1–3, p4 rarely present) posterior mac, one ms and one sens (ms antero-enternal to sens). Th. III with five (p1–4, p4i) mac and one sens (Fig. 79). Trochanteral organ with 25–31 smooth spiny chaetae (Fig. 80). Tenent hair ciliate and longer than inner edge of unguis, with tip capitate. Unguis with three inner teeth, basal pair located at 0.41–0.50 distance from base of inner edge of unguis, distal one small and at 0.75–0.76 distance from base; inner lamellae of unguiculus truncate, external lamellae acuminate (Fig. 81).

Abdomen. Range of Abd. IV length as 9.21–10.45 times dorsal axial length of Abd. III. Chaetotaxy Abd. I–III as in Fig. 82. Abd. I with five (a1, a3, m2–4, a1 rarely absent, a3 sometimes absent), one ms. Abd. II with two (m3, m3e) central, one (m5) lateral mac. Abd. III with two (pm6, p6) lateral mac, one ms and one sens. Lateral part of Abd. IV with 10–12 mac. Middle part of Abd. IV with two (A1, Ae1) mac anteriorly; four (A3, B3, Be1, C1) mac centrally; four or five (B4, B5, A6, A4 and A5 sometimes absent) posteriorly (Fig. 83). Abd. V with three sens, middle one posterior to m3 (Fig. 84). Anterior face of ventral tube with 11–15 ciliate chaetae, 3+3 of them as mac, line connecting proximal (Pr) and external-distal (Ed) mac oblique to median furrow (Fig. 85); posterior face with many ciliate chaetae; lateral flap with five or eight smooth and seven or 24 ciliate chaetae (Fig. 86). Mucro rectangle and with two teeth apically and one small tooth medio-distally (Figs 87–89).

The genus Akabosia was established by Kinoshita in 1919 and it can be separated from its similar genus Salina by the crenulated dens (dens is not crenulated in Salina). Only one species, A. matsudoensis Kinoshita, 1919, has been reported in the genus and its localities include Japan (Kinoshita 1919; Yosii 1954, 1965), Korea (Mitra 1977) and China (Zhang et al. 2015). The characters of our specimens agree well with their description in colour pattern, chaetotaxy of dorsal body, labrum and mucro, and we describe some additional characters including maxillary outer lobe, labial papilla E, chaetotaxy of Abd. V for the first time. The medio-distal tooth on the mucro was overlooked previously as it is very small and located on the lateral side.