Thailand, Kanchanaburi province, Sai Yok district, Tham (cave) Morakhot (14°11'02.7"N, 99°01'32.8"E, 426 m a.s.l.).

Holotype : female on slide, Kanchanaburi province: Sai Yok district, Tham (cave) Morakhot, 14°11'02.7"N, 99°01'32.8"E, 426 m a.s.l., 28 February 2019, S. Jantarit, A. Nilsai and K. Jantapaso leg., dark zone of cave, by aspirator (sample # THA_SJ_KRI12). Paratypes: 5 paratypes on slides (all subadults), same locality and date as the holotype.

Holotype and 5 paratypes deposited in NHM-PSU, measurements of holotype in Table 1.

Habitus. Highly troglomorphic, slender, with elongate legs, furca and antennae (Figs 2A, 16A). Length: 1.7–2.1 mm (n = 6) (body 1.5–1.7 mm, head 0.4–0.5 mm). Fourth abdominal segment 4–6 times (n = 6, female and 5 subadults) longer than the third one along the dorsal axis. Furca well developed, about 1.1–1.2 (n = 3) times shorter than body length. Body colour white, with spots of orange pigment. Eyes absent, no ocular patch.

Chaetal types. Four types of chaetae on somites, appendages (except antennae) and mouthparts: scales, present on antennal segment I and II, head, body and ventral side of the furca, absent on legs and ventral tube; ordinary chaetae on all body parts; S-chaetae and trichobothria on tergites; hairs devoid of sockets on outer maxillary lobe. Chaetal types on antennae are much more diverse and described separately further.

Pseudopores (Figs 2E, 3A–D, 4G, 5B, 6B, 6D). Pseudopores present as round flat disks larger than mac sockets, on antennae, head and tergites. Head pseudopore sometimes present asymmetrically on one side only (Fig. 2E). Dorsal pseudopore formula: 1/1, 1/1, 1, 1, 1+4 (Figs 2E, 3A–D). On antenna, 2 psp detected ventro-distally on Ant. I, 3 ventro-distally on Ant. II and 1 ventro-distally on Ant. III (Figs 5B, 6B, 6D). On head, 1 psp close to antennal basis (Fig. 2E). On legs, psp present externally on coxae (2 for legs I and II and 2–(3) for leg III). On manubrium, 2 psp on the dorso-distal plaque (Fig. 4G); on each dens, 4 psp dorso-basally near the internal spine row (Fig. 4G).

Mouthparts. Clypeus with 11 mac, symmetrically arranged: 9 ciliated posteriorly and 2 smooth anteriorly (Fig. 2F). Labral formula 4/5,5,4 (Fig. 2I; prelabral chaetae short, bent and ciliated, labral chaetae thinner, longer, smooth and acuminate, those of the distal row slightly larger and longer than those of the median row; its anterior line not concave in V or U-shape, contrary to T. kae (Jantarit et al. 2020). Ventro-distal complex of labrum well differentiated, asymmetrical, with 2 distal combs (a larger one with 8–12 teeth on the left side, a smaller one with 15–19 minute teeth on the right side) and an axial pair of sinuous tubules (Fig. 2C). Distal part of labrum not adorned with spines dorso-distally. Labial palp similar to that described by Fjellberg (1999) for Troglopedetes sp., with strong papillate chaetae. Number of guards for each major papillate chaetae: A (0), B (5), C (0), D (4) and E (4); lateral process subcylindrical, reaching above the apex of papilla E (Fig. 2B); 5 proximal chaetae. Chaetae of labial basis as M1m2rel1l2, with M1 ciliated, m2, e and l1 subequal and smooth, r shorter than others and smooth, l2 short, smooth and acuminate (Fig. 2H). Outer maxillary lobe with 1 papillate chaeta, 1 basal chaeta and 2 sublobal hairs, shorter than the others (Fig. 2G). Maxillary head with a 3-toothed claw, several stout shortly ciliated lamellae not observed in detail and 2 thin elongate structures (1 dorsally and 1 ventrally), like in T. kae (Jantarit et al. 2020). Mandible head strong, asymmetrical (left side with 4 teeth, right side with 5); molar plate with 3 strong pointed basal teeth, and other 2–3 inner distal teeth, identical in both mandibles.

Antennae (Figs 2A, 2D, 5–7). Antennae extremely elongated (2,175–2,780 µm, n = 6), 1.45–1.64 times longer than body+head length (n = 3), 5.5 times (n = 4) longer than the cephalic diagonal. Ant. IV subdivided into two segments, asymmetrically arranged with Ant. IVa longer than IVb (Fig. 7E) (0.6 : 0.4, n = 4), without apical bulb (Fig. 7C). Lengths of antennal segments I to IV (IVa+IVb) as 1:1.7:2:2.7 (average, n = 4). Antennal chaetae (scales, 5 types of ordinary chaetae, 14 types of S-chaetae and subapical organit) described separately.

General chaetotaxy (Figs 2E, 3A–D). Body densely covered with oval scales; ventro-lateral scales larger than dorsal ones; posterior scales of tergites larger than anterior ones (17–59 µm long).

Dorsal macrochaetae formula: 4,2/9,4/0,2,4,3 (Figs 2E, 3A). Trichobothrial pattern : 1/0, 0/0, 2, 3, 3 (Figs 2E, 3A). Trichobothrial complexes well developed with modified mes of various sizes (Fig. 3A–D), described below for each segment. The figured mes pattern is not complete.

Head chaetotaxy. Head with 10–11 peri-antennal mac in line on each side, with 4+4 central mac (chaetae A, B, D, G of Deharveng and Gers (1993); AMS = A3, M2, M1 and S3), absence of the chaetae C, E and F. Cephalic mes short, feebly serrated, equal, 9+9 symmetrically arranged (Fig. 2E). One lateral cephalic trichobothria much shorter than the closest mac on each side; suture zone not visible (Fig. 2E). Head dorsally densely covered with round to oval scales (25–35 µm long).

Ventral chaetotaxy of head densely covered with oval scales (65–72 µm long), postlabial chaetae along the linea ventralis as 3 smooth mes anteriorly and 2 smooth chaetae laterally, one mac and an oblique line of 7–8 mes posteriorly on each side (Fig. 2H).

Tergite chaetotaxy. Th. II with a collar consisting of a few rows of mac along its anterior and antero-lateral margins, a compact group of 6 central mac on each side (“P3 complex” of Soto-Adames et al. (2014) and 3 antero-lateral mac; 1 antero-lateral ms; 1 antero-lateral sens; 3 short mic postero-laterally, and a few others not counted centrally (Fig. 3A).

Th. III with 4 mac by side (a group of 3 central and 1 anterior to them), 1 sens at antero-lateral margins, and about 16 mac or long mes at lateral margins (Fig. 3A).

Abd. I without central mac, with 1 ms laterally on each side, a row of 3 mics below psp, a6 (sensu Soto-Adames 2015) absent, and 5 mes laterally (Fig. 3A).

Abd. II with 2 tric on each side and 6 modified mes around them (2 around the internal tric and 3–4 near external tric), 2 mac (1 near internal tric and 1 near external tric), 1 sens near internal tric, 2 mic close to external tric), at least 6 other mes sockets visible at lateral margins (not drawn) (Fig. 3A, B).

Abd. III with 3 tric on each side (1 internal, 2 external) and 9–10 modified mes around tric (3 near internal tric, 6–7 near the two external tric); 4 mac (1 near internal tric and 3 near external tric); 1 sens anterior to internal tric and ms not seen; at least 7 mes at lateral margins (Fig. 3A, C).

Abd. IV with 3 tric on each side (2 antero-lateral, 1 postero-lateral) and about 7–11 modified mes around the two antero-lateral tric; postero-lateral tric without modified mes. Mac distributed as 3 central on each side (1 antero-external to pseudopore, 2 anterior to posterior tergite margin), 1 near postero-lateral tric, and at least 4 external, mixed with at least 13 mes or smaller mac on lateral to posterior margins; 2 sens; at least 9 S-like chaetae sensu Lukić et al. (2015) anteriorly, and at least 5 mes or short S-like chaetae uniformly distributed; at least 3 serrated mes in line in the posterior row along pseudopore line, from medium to short size (Fig. 3A, D).

Abd. V with 2 sens detected on each side, and several ordinary chaetae from mes to mac, not counted (Fig. 3A). Abd. VI chaetotaxy not analyzed.

Legs (Fig. 4A–C). Legs long. Tita III 1.3–1.4 times longer than the head diagonal, slightly longer than Tita I and II. Legs devoid of scales, mostly covered with ordinary ciliated chaetae of various length, from mes to mac. Trochanteral organ of leg III with 19–21 smooth, straight, unequal spiny chaetae (n = 4) (Fig. 4E). Tibiotarsus chaetotaxy mostly composed of strong ciliated-serrated mes, the basal ones longer and thicker (52–69 µm), slightly shorter distally (up to 35–40 µm). Distal row with 9–10 subequal ciliated mes and a dorso-apical tenent hair clavate on tita; a ventro-distal strong smooth erected chaeta present on Tita III (Fig. 4B). Praetarsal mic minute (3.5–4 µm), clearly seen in one side (Fig. 4B). Unguis slender and long (56–66 µm long, 12–15 µm wide at basis), 10 times shorter than tita. Claw I and II with 2 strong unpaired inner teeth at 50–57% and 80–89%, and a pair of inner basal teeth of equal size (Fig. 4A); Claw III with a very tiny tooth at 88% of inner edge (Fig. 4B, C), outer edge with a minute tooth at 19–25% usually inconspicous; unguiculus pointed, narrow, lanceolate and elongate, 0.5–0.7 times shorter than the claw, its external edge with at least 9 toothlets (Fig. 4B).

Ventral tube (Fig. 4D). Ventral tube about 4 times longer than wide, with 3+3 long serrated mac anteriorly and 6 mes (2 ciliated and 4 smooth) on each lateral flap; posterior side not visible.

Furca complex (Fig. 4G, H). Tenaculum with 4 teeth on each ramus, of decreasing size from the basal to the distal one, on a prominent, irregular body, with a postero-basal strong, densely serrated, distally bent chaeta. Manubrium about 1.28 times (n = 5) shorter than the mucrodens (mucro+dens). Manubrium dorsally with subequal ciliated mes (none smooth), irregularly arranged in 3–4 rows in two longitudinal stripes separated by a glabrous axial stripe, external row of chaetae distally with at least 11 long ciliated mes, dorso-distal plaque with 4+4 mes and 2+2 pseudopores (Fig. 4G). Ventrally with a dense cover of round to oval (30–60 µm) and thin elongated scales (35–70 µm). Dens straight, elongate, hairy, slightly and progressively tapering, dorsally with 2 rows of spines, mixed with ciliated mes of various length, thickness and shape. Dorso-external row with 21–24 spines, dorso-internal row with 40–46 spines (asymmetries between dentes); external spines larger and less sclerotized than the internal ones. Some short ciliated mes interspersed with spines in the external row; dorsally between the two rows of spines a mix of short and long ciliated mes, irregularly arranged in one row distally turning to 3–4 rows proximally; laterally, many short ciliated mes; dorso-distally, 3–(4) stronger ciliated mes; 4+4 psp on dorso-basally between the two rows of spine (Fig. 4G). Dens ventrally entirely and densely scaled, the scales elongate (25–60 µm) (oval shape distally), arranged in short lines from 3–5 (distally) to 6–8 scales (proximally) (Fig. 4G). Mucro rather stout, short, 13.5–14.4 (average 14, n = 5) times shorter than dens (Fig. 4G, H), with 4 main teeth, the apical one blunt and strong, the subapical one acute and strong, a latero-distal one small and acute, and 1 dorso-basal, minute, acute and strong, acute with one toothlet basally (Fig. 4H).

Genital plate (Fig. 4F). Female genital plate with 2+2 mic.

Troglopedetes spectabilis sp. nov. exclusively inhabits a chamber in the dark zone of a cave. Specimens were found in an oligotrophic habitat with a very humid and wet environment on muddy ground. The air temperature in the chamber was 23.5–24.3 °C, soil temperature was 22.9–23.1 °C and the relative humidity was 84%. The cave is undisturbed and rather difficult to access (due to the steep slope up to the entrance). It is located in dry evergreen forest mixed with bamboo forest at moderate altitude (426 m. asl.). Some simple infastructure has been introduced into the cave, including a metal ladder at the entrance.

The species name is derived from the Latin word spectabilis, meaning “remarkable” or “admirable” and referring to its extremely long antennae.

Troglopedetes spectabilis sp. nov. is the most highly troglomorphic species of Troglopedetes. It is clearly distinct from other species of the genus by the extreme length of its appendages, especially the antennae (the ratio of antenna: head is 5.5), by its claw complex and by its furca (Table 1). Chaetae m2 and l1 of labial basis are smooth whereas they are ciliated in all other described species in the country. Central area of head has A, B, D, G macrochaetae. Dens of T. spectabilis sp. nov. is very long with 40–46 internal spines and 4 psp, while the other species of the genus in Thailand have only 2 psp. A most unexpected character of this species is the very different claw morphology of leg I–II and leg III checked in several specimens, which may have taxonomic and evolutionary implication that will be discussed in future works.

Thailand, Tak Province, Tha Song Yang district, Tham (cave) Mae Usu (17°18'15.0"N, 98°09'19.9"E, 172 m a.s.l.).

Holotype : female on slide, Tak Province: Tha Song Yang district, Tham (cave) Mae Usu, 17°18'15.0"N, 98°09'19.9"E, 145 m a.s.l., 7 March 2019, S. Jantarit, A. Nilsai and K. Jantapaso leg., dark zone of cave, by aspirator (sample # THA_SJ_TAK03). Paratypes: 5 paratypes on slides (all subadult), same locality and date as the holotype.

Holotype and 5 paratypes deposited in NHM-PSU, measurements of holotype in Table 2.

Habitus. Troglomorphic, slender, with elongate legs, furca and antennae. Length: 1.9–2.0 mm (n = 4) (body 1.4–1.6 mm, head 0.4 mm). Fourth abdominal segment 4–5 times (n = 4) longer than the third one along the dorsal axis. Furca well developed, about 1.4–1.5 (n = 3) times shorter than the body length. Body colour white with spots of orange pigment. Eyes not detected, but with 2+2 pigmented ocular patches.

Chaetal types. Four types of chaetae on somites, appendages (except antennae) and mouthparts: scales, present on antennal segment I and II, head, body and ventral side of the furca, absent on legs and ventral tube; ordinary chaetae on all body parts; S-chaetae and trichobothria on tergites; hairs devoid of sockets on outer maxillary lobe. Chaetal types on antennae are much more diverse and described separately further.

Pseudopores (Figs 8A, 9A–D, 11B). Pseudopores present as round flat disks larger than mac sockets, on antennae, head and tergites. Head pseudopore sometimes present aymmertrically on one side only. Dorsal pseudopore formula: 1/1, 1/1, 1, 1, 1+4 (Figs 8A, 9A–D). On antenna, 1 psp detected ventro-distally on Ant. I (Fig. 11B), without psp on Ant. II and Ant. III. On head, 1 psp close to antennal basis (Fig. 8A). On legs, psp present externally on coxae (1–(2) for legs I and II and 2 for leg III). On manubrium, 2 psp on the dorso-distal plaque; on each dens, 2 psp dorso-basally near the internal spine row.

Mouthparts. Clypeus with 13 large mes, symmetrically arranged: 9 ciliated posteriorly and 4 thin smooth anteriorly (Fig. 8F). Labral formula 4/5,5,4 (Fig. 8E); prelabral chaetae short, bent and ciliated, labral chaetae thinner, longer, smooth and acuminate, those of the distal row slightly larger and longer than those of the median row; the anterior line not concave in V or U-shape. Ventro-distal complex of labrum well differentiated, asymmetrical, with 2 distal combs (a larger one with 8–9 teeth on the left side, a smaller one with 13–14 minute teeth on the right side) and an axial pair of sinuous tubules. Distal part of labrum not adorned with spines dorso-distally. Labial palp similar to that described by Fjellberg (1999) for Troglopedetes sp., with strong papillate chaetae. Number of guards for each major papillate chaetae: A (0), B (5), C (0), D (4) and E (4); lateral process subcylindrical, surpassing the apex of papilla E (Fig. 8B); 5 proximal chaetae. Chaetae of labial basis as M1M2REL1l2, with M1, M2, R, E, L1 subequal and ciliated, l2 short, smooth and acuminate (Fig. 8G). Outer maxillary lobe with 1 papillate chaeta, 1 basal chaeta longer than the others and 2 sublobal hairs (Fig. 8C). Maxillary head with a 3-toothed claw, several stout shortly ciliated lamellae not observed in detail and 2 thin elongate structures (1 dorsally and 1 ventrally). Mandible head strong, asymmetrical (left side with 4 teeth, right side with 5); molar plate with 3 strong pointed basal teeth, and other 2–3 inner distal teeth, identical in both mandibles.

Antennae (Figs 11–13). Antennae elongated (1,274–1,524 µm, n = 4), slightly shorter than body+head length (n = 3), and 3.2 times (n = 4) longer than the cephalic diagonal. Ant. IV subdivided into two segments, asymmetrically arranged with Ant. IVa longer than IVb (0.57 : 0.43, n = 4), without apical bulb (Fig. 13D). Lengths of antennal segments I to IV (IVa+IVb) as 1:1.9:1.9:3 (average, n = 4). Antennal chaetae (scales, 5 types of ordinary chaetae, 13 types of S-chaetae and subapical organit) described separately.

General chaetotaxy (Figs 8A, 9A–D). Body scales densely covered with oval scales; ventro-lateral scales larger than the dorsal ones; posterior scales of tergites larger than the anterior ones (24–40 µm long).

Dorsal macrochaetae formula: 0,2/8,4/0,2,4,3 (Figs 8A, 9A). Trichobothrial pattern : 1/0, 0/0, 2, 3, 3 (Figs 8A, 9A). Trichobothrial complexes well developed with modified mes of various sizes (Fig. 9A–D) described below for each segment. The figured mes pattern not complete.

Head chaetotaxy (Fig. 8A, G). Head with 11–14 peri-antennal mac in line on each side, no central mac. Cephalic mes short, feebly serrated, equal, 15+15 symmetrically arranged (Fig. 8A). One lateral cephalic trichobothria much shorter than the closest mac on each side; suture zone not visible (Fig. 8A).

Head dorsally densely covered with round to oval scales (33–45 µm long). Ventral chaetotaxy of head densely covered with oval scales (57–67 µm long), postlabial chaetae along the linea ventralis as ciliated mes anteriorly and 3 ciliated chaetae laterally, one mac and an oblique line of 5–6 mes posteriorly on each side (Fig. 8G).

Tergite chaetotaxy (Fig. 9A–D). Th. II with a collar consisting of a few rows of mac along its anterior and antero-lateral margins, a compact group of 6 central mac on each side and 2 antero-lateral mac; 1 antero-lateral ms; 1 antero-lateral sens, mes to mic not counted centrally (Fig. 9A).

Th. III with 4 mac by side (a group of 3 central and 1 anterior to them), 1 sens at antero-lateral margins, and about 12 mac or long mes at lateral margins (Fig. 9A).

Abd. I without central mac, with 1 ms laterally on each side, a row of 3 mics below psp, a6 absent, and 5 mes laterally (Fig. 9A).

Abd. II with 2 tric on each side and 6 modified mes around them (2 around the internal tric and 4 near external tric), 2 mac (1 near internal tric and 1 near external tric), 1 sens near internal tric, 4 mic (1 close to internal tric and 3 close to external tric), at least 3 other mes at lateral margins (Fig. 9A, B).

Abd. III with 3 tric on each side (1 internal, 2 external) and 8 modified mes around tric (2 near internal tric, 6 near the two external tric); 4 mac (1 near internal tric and 3 near external tric); 1 sens anterior to internal tric and 1 ms; at least 5 mes to small mac at lateral margins (Fig. 9A, C).

Abd. IV with 3 tric on each side (2 antero-lateral, 1 postero-lateral) and about 7 modified mes around the two antero-lateral tric; postero-lateral tric with 1 modified mes. Mac distributed as 3 central on each side (1 antero-external to pseudopore, 2 anterior to posterior tergite margin), 1 near postero-lateral tric, and at least 5 external, mixed with at least 14 mes or smaller mac on lateral to posterior margins; 3 sens; at least 4 S-like chaetae sensu Lukić et al. (2015) anteriorly, and at least 5 mes or short S-like chaetae uniformly distributed; at least 1 serrated mes in line in the posterior row along pseudopore line (Fig. 9A, D).

Abd. V with 2 sens detected on each side, and several ordinary chaetae from mes to mac, not counted (Fig. 9A). Abd. VI chaetotaxy not analyzed.

Legs (Fig. 10A, B). Legs long. Tita III as long as the head diagonal, slightly longer than Tita I and II. Legs devoid of scales, mostly covered with ordinary ciliated chaetae of various length, from mes to mac. Trochanteral organ of leg III with 15–17 smooth, straight, unequal spiny chaetae (n = 3) (Fig. 10B). Tibiotarsus chaetotaxy mostly composed of strong ciliated-serrated mes, the basal ones longer and thicker (50–70 µm), slightly shorter distally (up to 35–45 µm). Distal row with 7–9 subequal ciliated mes and a dorso-apical tenent hair thin, pointed on all tita; a ventro-distal strong smooth erected chaeta present on Tita III (Fig. 10A). Praetarsal mic minute (3.5–4 µm), clearly seen in one side (Fig. 10A). Unguis in all legs slender and long (60–65 µm long, 13 µm wide at basis), 7 times shorter than tita, with a pair of inner basal teeth of equal size, one uneven inner basal tooth, outer edge with a minute tooth at 20–23% usually inconspicous; unguiculus pointed, narrow, lanceolate and elongate, about 0.6–0.7 times shorter than the claw, its external edge irregular with at least 4–9 toothlets (Fig. 10A).

Ventral tube (Fig. 10D, E). Ventral tube about 3.8 times longer than wide, with 3+3 long serrated mac anteriorly and 7 mes (3 ciliated and 4 smooth) on each lateral flap (Fig. 10E); posterior side with at least 39 ciliated mes, 2 smooth mes and 7 small spines (Fig. 10D).

Furca complex (Fig. 10C). Tenaculum with 4 teeth on each ramus, of decreasing size from the basal to the distal one, on a prominent, irregular body, with a postero-basal strong, densely serrated, distally bent chaeta. Manubrium about 1.13 times (n = 4) shorter than the mucrodens (mucro+dens). Manubrium dorsally with subequal ciliated mes (none smooth), irregularly arranged in 3–4 rows in two longitudinal stripes separated by a glabrous axial stripe, external row of chaetae distally with at least 11–19 long ciliated mac, dorso-distal plaque with 4+4 mes and 2+2 pseudopores. Ventrally with a dense cover of round to oval (25–57 µm long) and thin elongated scales (25–40 µm long). Dens straight, elongate, hairy, slightly and progressively tapering, dorsally with 2 rows of spines, mixed with ciliated mes of various length, thickness and shape. Dorso-external row with 23–28 spines, dorso-internal row with 33–40 spines (asymmetries between dentes); external spines larger and less sclerotized than the internal ones. Some short ciliated mes interspersed with spines in the external row; dorsally between the two rows of spines a mix of short and long ciliated mes, irregularly arranged in one row distally turning to 3–4 rows proximally; laterally, many short ciliated mes; dorso-distally, 3–(4) stronger ciliated mes; 2+2 psp on dorso-basally between the two rows of spine. Dens ventrally entirely and densely scaled, the scales elongate (15–27 µm long) (oval shape distally), arranged in short lines from 3–5 (distally) to 6–8 scales (proximally). Mucro rather stout, short, 10.6–12.1 (n = 4) times shorter than dens, with 4 main teeth, the apical one blunt and strong, the subapical one acute and strong, a latero-distal one small and acute, and 1 dorso-basal, minute, acute and strong, with one toothlet basally (Fig. 10C).

T. takensis sp. nov. is only known from a large chamber in the dark zone of a cave. Specimens were found as small populations in an oligotrophic habitat, i.e. on the wall and ground surface, with a very humid and wet environment, with small trace of organic matter. Air temperature in the chamber was 22.2–23.0 °C, soil temperature was 21.9 °C and the relative humidity was 85%.

The species name is derived from the name of the province (Tak) where it was found.

Troglopedetes takensis sp. nov. has elongated antennae (the ratio of antenna: head is 3.2), legs and furca (Table 2), but shorter than in T. spectabilis sp. nov. It presents two distinct black small eye-patches on each side and lacks central mac on the head. Claws usually have only one uneven inner basal tooth (with 2 specimens without uneven inner tooth on claw III). T. takensis sp. nov. shares with T. calvus Deharveng & Gers, 1993 the absence of central mac on head. However, the new species differs from T. calvus in size (1.9–2.0 vs 0.9–1.4), presence of eyes-patches (2+2 vs 0), length of antenna (1,274–1,524 µm vs 747 µm), tenent hair (pointed vs clavate), inner teeth of claw ((0)1 vs 2), internal row of dental spines (33–40 vs 14–32).

Thailand, Kanchanaburi Province, Sai Yok district, Tham (cave) Khang Khao (14°11'23.8"N, 98°59'37.0"E, 262 m a.s.l).

Holotype : male on slide, Kanchanaburi Province: Sai Yok district, Tham (cave) Khang Khao, 14°11'23.8"N, 98°59'37.0"E, 262 m a.s.l., 28 February 2019, S. Jantarit, A. Nilsai and K. Jantapaso leg., dark zone of cave, by aspirator (sample # THA_SJ_KRI11). Paratypes: 2 subadults on slides, same locality and date as the holotype.

Holotype and 2 paratypes deposited in NHM-PSU, measurements of holotype in Table 3.

Habitus. Troglomorphic, slender, with elongate legs, furca and antennae. Length: 1.2–1.3 mm (n = 3) (body 0.9–1.0 mm, head 0.2–0.3 mm). Fourth abdominal segment 4–5 times (n = 3, 1 male and 2 subadults) longer than the third one along the dorsal axis. Furca well developed, about 1.4–1.5 (n = 3) times shorter than body length. Body colour white with spots of orange pigment. Eyes absent, no ocular patch.

Chaetal types. Four types of chaetae on somites, appendages (except antennae) and mouthparts: scales, present on antennal segment I and II, head, body and ventral side of the furca, absent on legs and ventral tube; ordinary chaetae on all body parts; S-chaetae and trichobothria on tergites; hairs devoid of sockets on outer maxillary lobe. Chaetal types on antennae are much more diverse and described separately further.

Pseudopores (Figs 14C, 15A–D). Pseudopores present as round flat disks larger than mac sockets, on antennae, head and tergites. Dorsal pseudopore formula: 1/1, 1/1, 1, 1, 1+4 (Figs 14C, 15A–D). On antenna, 1 psp detected ventro-distally on Ant. I, 1 psp on Ant. II, Ant. III and Ant.IVb. On head, 1 psp close to antennal basis (Fig. 14C). On legs, psp present externally on coxae (1 for legs I and 2 for legs II and III). On manubrium, 2 psp on the dorso-distal plaque; on each dens, 2 psp dorso-basally near the internal spine row

Mouthparts. Clypeus not visible. Labral formula 4/5,5,4; prelabral chaetae short, bent and ciliated, labral chaetae thinner, longer, smooth and acuminate, those of the distal row slightly larger and longer than those of the median row; the anterior line not cleary seen. Ventro-distal complex of labrum well differentiated, asymmetrical, with 2 distal combs (a larger one with 9–10 teeth on the left side, a smaller one with 10–12 minute teeth on the right side) and an axial pair of sinuous tubules. Distal part of labrum not adorned with spines dorso-distally. Labial palp similar to that described by Fjellberg (1999) for Troglopedetes sp., with strong papillate chaetae. Number of guards for each major papillate chaetae: A (0), B (5), C (0), D (4) and E (4); lateral process subcylindrical, surpassing the apex of papilla E (Fig. 14B); 5 proximal chaetae. Chaetae of labial basis as M1M2REL1l2, with M1, M2, E and L1 subequal and ciliated, R shorter than others and ciliated, l2 short, smooth and acuminate (Fig. 14D). Outer maxillary lobe with 1 papillate chaeta, 1 basal chaeta and 2 sublobal hairs (Fig. 14A). Maxillary head with a 3-toothed claw, several stout shortly ciliated lamellae not observed in detail and 2 thin elongate structures (1 dorsally and 1 ventrally). Mandible head strong, asymmetrical (left side with 4 teeth, right side with 5); molar plate with 3 strong pointed basal teeth, and other 2–3 inner distal teeth, identical in both mandibles.

Antennae. Antennae (743–905 µm, n = 3), shorter than body+head length (n = 3), 3.1 times (n = 3) longer than the cephalic diagonal. Ant. IV subdivided into two segments, asymmetrically arranged with Ant. IVa longer than IVb (0.57 : 0.43, n = 3), without apical bulb. Length of antennal segments I to IV (IVa+IVb) as 1:2.4:2.2:3.6 (n = 2). Antennal chaetae (scales, 5 types of ordinary chaetae, 13 types of S-chaetae and subapical organit).

General chaetotaxy (Figs 14C, 15A–D). Body scales densely covered with round to oval scales, the scales in ventro-lateral is larger than the dorsal side and posterior scales of tergites larger than the anterior ones (20–40 µm long). Dorsal macrochaetae formula: 3,4/8,4/0,2,4,3 (Figs 14C, 15A). Trichobothrial pattern : 1/0, 0/0, 2, 3, 3 (Figs 14C, 15A). Trichobothrial complexes well developed with modified mes of various sizes (Fig. 15A–D) described below for each segment. The figured mes pattern is not complete.

Head chaetotaxy (Fig. 14C, D). Head with 12–13 peri-antennal mac in line on each side, with 3+3 central mac (chaetae A, C and E); AMS = A3, S5 and S3), absence of the chaetae B, D, F and G. Cephalic mes short, feebly serrated, equal, 10+10 symmetrically arranged (Fig. 14C). One lateral cephalic trichobothria much shorter than the closest mac on each side; suture zone not visible (Fig. 14C). Head dorsally densely covered with round to oval scales (25–45 µm long). Ventral chaetotaxy of head densely covered with oval scales (40–50 µm long), postlabial chaetae along the linea ventralis as ciliated mes anteriorly and 3 ciliated chaetae laterally, one mac and an oblique line of 4 mes posteriorly on each side (Fig. 14D).

Tergite chaetotaxy (Fig. 15A–D). Th. II with a collar consisting of a few rows of mac along its anterior and antero-lateral margins, a compact group of 6 central mac on each side and 2 antero-lateral mac; 1 antero-lateral ms; 1 antero-lateral sens, and other mes not counted centrally (Fig. 15A).

Th. III with 4 mac by side (a group of 3 central and 1 anterior to them), 1 sens at antero-lateral margins, and about 9 mac or long mes at lateral margins (Fig. 15A).

Abd. I without central mac, with 1 ms laterally on each side, a row of 3 mics below psp, a6 absent, and 5 mes laterally (Fig. 15A).

Abd. II with 2 tric on each side and 7 modified mes around them (2 around the internal tric and 5 near external tric), 2 mac (1 near internal tric and 1 near external tric), 1 sens near internal tric (Fig. 15A, B), 3 mic (1 close to internal tric and 2 close to external tric), at least 1 other mes socket at lateral margins.

Abd. III with 3 tric on each side (1 internal, 2 external) and 7 modified mes around tric (2 near internal tric, 5 near the two external tric); 4 mac (1 near internal tric and 3 near external tric); 1 sens anterior to internal tric and 1 ms; at least 6 mic to mes at lateral margins (Fig. 15A, C).

Abd. IV with 3 tric on each side (2 antero-lateral, 1 postero-lateral) and about 7 modified mes around the two antero-lateral tric; postero-lateral tric with 1 modified mes. Mac distributed as 3 central on each side (1 antero-external to pseudopore, 2 anterior to posterior tergite margin), 1 near postero-lateral tric, and at least 5 external, mixed with at least 13 mes or smaller mac on lateral to posterior margins; 3 sens; at least 5 S-like chaetae sensu Lukić et al. (2015) anteriorly, and at least 2 mes or short S-like chaetae uniformly distributed; at least 1 serrated mes in line in the posterior row along pseudopore line (Fig. 15A, D).

Abd. V with 2 sens detected on each side, and several ordinary chaetae from mes to mac, not counted (Fig. 15A). Abd. VI chaetotaxy not analyzed.

Legs (Fig. 14E). Legs long. Tita III as long as the head diagonal, slightly longer than Tita I and II. Legs devoid of scales, mostly covered with ordinary ciliated chaetae of various length, from mes to mac. Trochanteral organ of leg III with 13 smooth, straight, unequal spiny chaetae. Tibiotarsus chaetotaxy mostly composed of strong ciliated-serrated mes, the basal ones longer and thicker (33–48 µm), slightly shorter distally (up to 20–34 µm). Distal row with 8 subequal ciliated mes and a dorso-apical tenent hair thin, smooth and pointed; a ventro-distal strong smooth erected chaeta present on Tita III. Praetarsal mic minute (2.5–3 µm), present in both sides. Unguis slender and long (29–38 µm long, 7 µm wide at basis), 8.9 times shorter than tita, with one inner tooth, and a pair of inner basal teeth of unequal size, outer edge with a minute tooth at 40–42%; unguiculus pointed, narrow, lanceolate and elongate, about 0.6–0.7 time shorter than the claw, its external edge with at least 4 toothlets (Fig. 14E).

Ventral tube (Fig. 14F). Ventral tube about 3.1 times longer than wide, with 3+3 long serrated mac anteriorly and 8 mes (5 ciliated and 3 smooth) on each lateral flap; posterior side not visible (Fig. 14F).

Furca complex. Tenaculum with 4 teeth on each ramus, of decreasing size from the basal to the distal one, on a prominent, irregular body, with a postero-basal strong, densely serrated, distally bent chaeta. Manubrium about 1.13 times (n = 3) shorter than mucrodens (mucro+dens). Manubrium dorsally with subequal ciliated mes (none smooth), irregularly arranged in 3–4 rows in two longitudinal stripes separated by a glabrous axial stripe, external row of chaetae distally with at least 10 long ciliated mac, dorso-distal plaque with 4+4 mes and 2+2 pseudopores. Ventrally, with a dense cover of round to oval (15–25 µm long) and thin elongated scales (25–30 µm long). Dens straight, elongate, hairy, slightly and progressively tapering, dorsally with 2 rows of spines, mixed with ciliated mes of various length, thickness and shape. Dorso-external row with 16–18 spines, dorso-internal row with 29 spines (asymmetries between dentes); external spines larger and less sclerotized than the internal ones. Some short ciliated mes interspersed with spines in the external row; dorsally between the two rows of spines a mix of short and long ciliated mes, irregularly arranged in one row distally turning to 3–4 rows proximally; laterally, many short ciliated mes; dorso-distally, 3–(4) stronger ciliated mes; 2+2 psp on dorso-basally between the two rows of spine. Dens ventrally entirely and densely scaled, the scales elongate (25–40 µm long) (oval shape distally), arranged in short lines from 3–5 (distally) to 6–8 scales (proximally). Mucro rather stout, short, 8.9–9.2 (n = 3) times shorter than the dens, with 4 main teeth, the apical one blunt and strong, the subapical one acute and strong, a latero-distal one small and acute, and 1 dorso-basal, minute, acute and strong, with one toothlet basally (Fig. 14G).

Genital plate (Fig. 14H). Male genital plate with 19 mic around the edge and 4 mic inside (Fig. 14H)

Troglopedetes rungsimae sp. nov. is only known from a small chamber in the dark zone of a cave. Specimens were found as small populations in an oligotrophic habitat, i.e. on the wall and ground with a very humid and wet environment, without any trace of organic matter. Air temperature in the chamber where specimens were collected was 23.5–24.8 °C, soil temperature was 23.1–23.3 °C and relative humidity was 88–91%.

The species is named in honour of Rungsima Tanthalakha, the Senior Program Director, Research Management and Innovation Management, National Science and Technology Develoment Agency, Thailand, who is interested in karst and cave biodiversity and for her contributions to the study of cave Troglopedetes in Thailand.

Troglopedetes rungsimae sp. nov. has the sixth most elongated antennae of the Troglopedetes species of Thailand (Table 3) after T. spectabilis sp. nov., T. multispinosus Deharveng & Gers, 1993, T. longicornis Deharveng & Gers, 1993, T. takensis sp. nov. and T. microps Deharveng & Gers, 1993. It is similar to T. dispersus Deharveng & Gers, 1993 (which has been recorded from two caves in Kanchanaburi province: Tham Lawa and Tham Kaew), in the absence of eyes, and the dorsal macrochaetotaxy of the central head (with A, C, E mac). However, it differs from it by its longer antennae (almost 1 versus 0.6 time shorter than the body), outer maxillary lobe chaetotaxy (1 vs 2), chaetae on lateral flap of the ventral tube (8+8 versus 7+7), and higher ratio of dens: mucro (9.1 vs 8.5).

In the same cave, we found another morphotype with a different claw morphology. This type has thin, smooth and clavate tenent hair on all tita (one pointed on Claw I). Claw is long and slender with 2 strong inner teeth, one tooth at 57–73% of inner edge and the other at a 90–91% of inner edge, and a pair of inner basal teeth of unequal size. One small tooth is at 40% on the outer edge. Unguiculus is pointed, narrow, lanceolate and elongate, about 0.65 time shorter than the claw, and its external edge is with 7 toothlets (Fig. 14I). However, its dorsal chaetotaxy is the same as T. rungsimae sp. nov. Unfortunately, the material available is not sufficient to described it in detail.