Three new species of cave Troglopedetes (Collembola, Paronellidae, Troglopedetinae) from Thailand, with a key to the Thai species

Thailand is today the richest country for the genus Troglopedetes Joseph, 1872, with 17 species described from the country. In this study three troglomorphic new species are described from caves in the western region. They are T. spectabilis sp. nov. and T. rungsimae sp. nov. from Kanchanaburi province and T. takensis sp. nov., from Tak province. The three new species share elongated antennae and have the same number of central mac on Th. III and Abd. IV. However, they differ from one another by the combination of: presence of eyes, antennal length, claw morphology, central head macrochaetotaxy and internal row of dental spines. Troglopedetes spectabilis sp. nov. is remarkably different from its congeners by its extreme long appendages, especially the antennae (ratio antenna: head = 5.5). In the second part of the paper the arrangment of antennal chaetotaxy and the diversity of its phaneres is analyzed in the three new species, homologized and compared with those of two other species described from Thailand (T. meridionalis and T. kae). A total of 22 types of chaetae have now been recognized among the species. A new type of S-chaetae for the genus was discovered in this study. There are 5 types of ordinary chaetae, 15 types of S-chaetae, the subapical organite of Ant. IV and scales. A total of 1,107 to 2,183 antennal chaetae on each side were observed, which includes 308–485 S-chaetae, 687–1,402 ordinary chaetae, 72–295 scales and a subapical organite.

Troglomorphic features in Collembola mostly comprise: large body size, elongated appendages (antennae, legs and furca), elongated and slender claw complex, pointed tenent hair, multiplication of antennal chaetae, blindness and depigmentation (Christiansen 2012; Lukić et al. 2018;Jantarit et al. 2019;Lukić 2019). The Troglopedetes species is so far described from Thailand exhibit various degrees of troglomorphy. Most of them are blind (only T. leclerci and T. microps have eyes), some are pigmented with orange dots, while others are white. They have various body sizes and antennal lengths, claw and furca morphologies. Among the 14 described species from Thailand, only T. multispinosus and T. longicornis display marked troglomorphic characters by having the most elongated antennae (ratio of antennae: body = 0.9 and 0.8 respectively), larger body size (1.8-2.2 mm), slender claw complex and pointed tenent hairs. The other described species have shorter antennae (ratio of antennae: body = 0.4-0.6), shorter body length (0.7-1.7 mm) and different claw complex morphology (Deharveng 1988a(Deharveng , 1990Deharveng and Gers 1993;. During our sampling campaigns in limestone caves in Thailand, several Troglopedetes species were collected. Three of them, which were found in caves in the western region (Tak and Kanchanaburi provinces), are described in this study. One of them exhibits strikingly long antennae, not seen in any other species of the genus (ratio of antennae: head > 3 times; antennae: body ≥ 1).
We have already described a high diversity of phaneres on antennae of two species of Troglopedetes , expecting that the antennal chaetotaxy could bring valuable information at the taxonomic level, as they do in Poduromorpha (Deharveng 1981), and could be used as important tools once patterns in other Entomobryoidea are better understood ). In the second part of this paper, we complete the data obtained so far by analysing, homologising and comparing the antennal chaetotaxy of the three new species with that of T. meridionalis and T. kae from Thailand, which have been previously described in this respect. A complete catalogue of all antennal chaetae is also provided. One of the three new species has extremely elongated antennae and is of special interest, as the increase in the number of sensory chaetae on the antennae of modified cave species has been considered in the literature as a troglomorphic trend in the genus Pseudosinella Schäffer, 1897 (Deharveng 1988b). The third part of the paper is a key to the species of the genus in Thailand.

Materials and methods
The specimens of the three new species were collected in the dark zone of caves in Tak and Kanchanaburi Province (Fig. 1). Collembola were detected by eye and then collected by aspirator. They were stored in 95% ethanol. For microscopical observation, they were mounted on slides in Marc Andre II medium after clearing in lactic acid. Morphological characters were examined under a light microscope using Leica DMLB and Leica DM1000 LED microscope with phase-contrast. Drawings were made using a drawing tube, and figures were improved with Adobe Photoshop and Illustrator CC/PC (Adobe Inc.).

Conventions for describing pseudopore and chaetotaxic patterns
Pseudopore arrangement follows  and . Types of phaneres follows . Formula of tergite pseudopores is given by half-tergite from Th. II to Abd. IV (Jantarit et al. 2013). Formula for labium basis chaetae follows the system of Gisin (1967), with upper-case letters for ciliated and lower-case letters for smooth chaetae. Labial chaetotaxy follows Fjellberg (1999). Dorsal chaetotaxy and chaetal areas of the head follow Deharveng and Gers (1993), Jordana and Baquero (2005) and Mitra (1993). Dorsal macrochaetotaxy description combines notation of individual chaetae derived from Szeptycki (1979) with chaetal group notation (rationale in Soto-Adames et al. 2014 and. Formula of dorsal macrochaetae and trichobothria are given by half-tergite from head to Abd. IV; for S-chaetae, by half-tergite from head to Abd. V. S-chaetae terminology of tergites follows Zhang and Deharveng (2014) and .
Holotype and 5 paratypes deposited in NHM-PSU, measurements of holotype in Table 1.
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; Schaetae and trichobothria on tergites; hairs devoid of sockets on outer maxillary lobe. Chaetal types on antennae are much more diverse and described separately further.
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. 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. 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.
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 posterobasal 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. Ecology. 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.
Etymology. The species name is derived from the Latin word spectabilis, meaning "remarkable" or "admirable" and referring to its extremely long antennae.
Remarks. 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. Type material. 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.
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; Schaetae and trichobothria on tergites; hairs devoid of sockets on outer maxillary lobe. Chaetal types on antennae are much more diverse and described separately further.
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  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).
Ecology. 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%.
Etymology. The species name is derived from the name of the province (Tak) where it was found.
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; Schaetae 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,. 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.
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) Ecology. 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%.
Etymology. 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.
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.

Distribution of the genus Troglopedetes in Thailand and Southeast Asia
The genus Troglopedetes in Thailand is dominant in the subterranean environment in the northern and western regions and is present in the mountain range bordering Myanmar (unpublished data). It is also spread over a wide area of the central plain region where karst is extremely fragmented (Fig. 1). Troglopedetes is rarely found in the southern pen-insula where only two recently described species are known . These are the only records of the genus from south of the Kra Isthmus, a hypothetical zoogeographical boundary that was earlier thought to separate the two closely related genera Troglopedetes and Cyphoderopsis Carpenter, 1917(Deharveng 1987Deharveng and Bedos 2001). The genus Cyphoderopsis, apart from the species found in India and Nepal, remains restricted to the south of the Kra Isthmus from the Thai-Malay peninsula to Western Indonesia, with a small number of species described (Jantarit et al. 2013). Interestingly, Troglopedetes is not present in the east and northeast regions of Thailand (Fig. 1), although many caves have been sampled there. The long Phet chabun-Dong Phaya Yen-Sankamphaeng mountain range, which stretches approximately north to south between the central plain and northeast region of Thailand, may have acted as a barrier to limit the dispersion of the genus Troglopedetes in Thailand. The genus is absent from the caves of southern Cambodia (unpublished data) and southern Vietnam , where it is replaced by the radiation of another Paronellidae genus, Lepidonella Yosii, 1960 (Deharveng andBedos 1995). At least one undescribed species of Troglopedetes is reported from Luang Prabang in Laos (Besson et al. 2001), at a similar latitude to Mae Sai district, Chiang Rai province in northern Thailand, which is the northernmost record of the genus in Thailand. The large gaps in our knowledge of the countries surrounding Thailand obviously needs to be filled to provide a decent overview of the distribution limits of the genus in Southeast Asia.
Cave Troglopedetes in Thailand exhibit various degrees of adaption to cave life (troglomorphy), from a small set of morphological modifications to a complete set of darkness adaptions, as is also presented in the genus Coecobrya Yosii, 1956(Jantarit et al. 2019. Two types of morphology are recognized among Thai Troglopedetes (Fig.  16). The first form is characterized by short appendages, short and rather swollen claw, small size (0.6-1.2 mm), and eyes and/or ocular patches generally present (Fig. 16C). Species of this form are usually associated with eutrophic habitats, especially guano piles, and are never troglomorphic. The second form has long to very long appendages (antennae, legs and furca), eyes are generally absent, slender claws and body size usually larger (1.3-2.2 mm) (Fig. 16A, B). Species of this form are mostly linked to oligotrophic cave habitats in wet and moist environments. They are very rare, with only six described species so far (T. spectabilis sp. nov., T. multispinosus, T. longicornis, T. takensis sp. nov., T. microps and T. rungsimae sp. nov.). However, some individuals of these species can also be found in guano patches in the dark zone of caves. Cave Troglopedetes of both morphological types all have very limited distribution ranges in Thailand.

Antennal phaneres
Phanere types and their arrangement pattern on each antennal segment that we recognised in the three new species are homologised and compared with the two species currently described from Thailand (T. meridionalis and T. kae, see details in . A total of four kinds of antennal phaneres are recognised in Thai Troglopedetes, as described in : scales, ordinary chaetae, S-chaetae and the subapical organite of Ant. IV. In finer detail, there is one type of scale, 5 types of ordinary chaetae and 15 types of S-chaetae. A total of 22 types can therefore be recongnized based on morphological grounds. For the scales (see , only an oval shape (15-50 µm Í 7-30 µm) is found on antennae, present dorsally only on Ant. I (19-127 scales) and II (25-152 scales) and ventrally on Ant. II (16-127 scales), absent ventrally on Ant. I, and absent on Ant. III and IV (Fig. 3A, C, D, Table 4, 5) Regarding ordinary chaetae, the five types mentioned above are present in the new species and their position is the same as described by ; figure not provided here).
With reference to the S-chaetae (sensu Deharveng 1983), they are present on all antennal segments, with a variety of thickness, shape and size (from mic to mes in size, 2-46 µm). According to , 14 types (type 1-14) of S-chaetae are described in T. kae and 13 types (type 1-13) in T. meridionalis. In this study, 14 types were found in T. spectabilis sp. nov. (type 1-6, 8-15), 13 types in T. takensis sp. nov. (type 1-6, 8-13, 15) and in T. rungsimae sp. nov. (type 1-13). A total of 15 S-chaetae types are now recognized in the antennae of Thai Troglopedetes. Extreme diversity of antennal S-chaetae is therefore retrieved in all species examined so far, and comprises the same types of chaetae, as only a single new type has been detected (type 15) which is found exclusively in the elongated antennae of T. spectabilis sp. nov. and T. takensis sp. nov. The types 1 to 14 are described in the study of , and characterized below; their position on antennae is given in Table 4.

Diversity and distribution patterns of antennal phaneres
The number of antennal phanneres used for the analysis and comparison in this study was observed from the holotype of each species. We counted a total of 741 to 2,183 chaetae per antenna for the 5 studied species of Thai Troglopedetes, including 207-485 S-chaetae, 483-1,402 ordinary chaetae, 48-295 scales and a single subapical organite (Tables 4 and 5). Overall, 2,183, 1,227 and 1,107 antennal chaetae were recorded in T. spectabilis sp. nov., T. takensis sp. nov. and T. rungsimae sp. nov. respectively. On a single antenna, 485 S-chaetae were numbered for T. spectabilis sp. nov., 308 for T. takensis sp. nov. and 348 for T. rungsimae sp. nov. Likewise, ordinary chaetae on a single antenna numbered 1,402 for T. spectabilis sp. nov., 790 for T. takensis sp. nov. and 687 for T. rungsimae sp. nov.
The The distribution of the different types of S-chaetae along with the antennal segments is arranged in more or less clearly defined patterns which are described below, compared with T. meridionalis and T. kae in the following paragraphs, summarised in Tables 4 and 5, and illustrated in Figures 5-7, 11-13.
First antennal segment: eight types of S-chaetae can be recognised (Figs 5A, B, 11A, B): type 3, type 5, type 6, type 8, type 9, type 10, type 12 and type 13 (type 13 is found exclusively in T. takensis sp. nov.). Only one type is present on the dorsal side (type 6), the others are located on the ventral side.
Second antennal segment: nine types of S-chaetae can be recognised (Figs 6A, B, 12A, B): type 2, type 3, type 4, type 6, type 7, type 8, type 10, type 13 and type 14. Three types are present on the dorsal and ventral side (type 2, type 4 and type 8). Three types on the dorsal side (type 3, type 6 and type 14) and three types on the ventral side (type 7, type 10 and type 13).
Third antennal segment: eight types of S-chaetae can be recognised (Figs 6C, D, 12C, D): type 1, type 4, type 5, type 7, type 8, type 13, type 10 and type 15. They are present on the dorsal and ventral side except type 13 which is only present on the ventral side. AIIIO has typically 5 S-chaetae: one chaeta of type 1, two chaetae of type 4 and two chaetae of type 5 (Figs 6C, D, 11C, 12D).
All are present on the dorsal and ventral side, except two types (1 and 9) that are present on the ventral side only and one type (7) that is present on the dorsal side only. They are distributed as follows on each subsegment.
Fourth antennal segment I (a): seven types of S-chaetae can be recognised: type 1, type 8, type 9, type 10, type 11, type 13, type 15. They are present on the dorsal and ventral side, except two types (1 and 9) that are present on the ventral side only.
Fourth antennal segment II (b): six types of S-chaetae can be recognised: type 4, type 7, type 8, type 10, type 11 and type 15. They are present on the dorsal and ventral side, except one type (7) that is present on the dorsal side only and one type (15) that is present on the ventral side only.
The most frequent antennal S-chaetae are type 8 (from 65 to 137 chaetae) and type 10 (from 36 to196 chaetae), which are present along all antennal segments. The other types are specific to three, two or a single segment(s) ( Table 4, 5). A new type (type 15) is found exclusively on the extremely long antennae of T. spectabilis sp. nov. and T. takensis sp. nov. on Ant. III and IV and is absent in T. rungsimae sp. nov., T. kae and T. meridionalis.
With regard to the abundance of S-chaetae along antennal segments, the result for the new species is similar to that in T. meridionalis and T. kae where type 8 is the most common followed by type 11 and 10 (Tables 4 and 5). Likewise, Ant. IV has the highest number of S-chaetae in all the new species followed by Ant. III, I and II in T. spectabilis sp. nov., and followed by Ant. III, II and I in T. takensis sp. nov. and T. rungsimae sp. nov. (Table 5), while ordinary chaetae abundance ranks as Ant. IV, III, II and I in T. spectabilis sp. nov. and T. takensis sp. nov. and Ant. IV, II, III and I in T. rungsimae sp. nov. ( Table 5).
The distal subsegment of antenna IV (Ant. IVb) is richer in S-chaetae than the proximal subsegment (Ant. IVa) in T. takensis sp. nov. and T. rungsimae sp. nov., but the number of S-chaetae is similar in T. spectabilis sp. nov.. The ordinary chaetae are more numerous in the proximal subsegment (Ant. IVa) than in the distal subsegment (Ant. IVb) in T. takensis sp. nov. and T. rungsimae sp. nov., but the number is rather similar in T. spectabilis sp. nov. ( Table 5).
Comparison of the diversity of antennal chaetae between the three new species, Troglopedetes kae and T. meridionalis Antennal chaetotaxy in Thai Troglopedetes is clearly plurichaetotic and extremely complex. Overall 22 types of antennal chaetae have been recognized. They are ordinary chaetae (5 types), S-chaetae (15 types), the subapical organite of Ant. IV and scales. According to , 12 chaetal types were located at fixed positions on antennal segments. However, with the 3 additional species from this study considered in addition to T. meridionalis and T. kae described in , fixed positions of antennal chaetae are left for only 7 types. They are 4 types of ordinary mes (type 1-4); 3 types of S-chaetae (type 11, 12) and the subapical organite of Ant. IV (Tables  4 and 5). Their diversity and distribution on the antennae are rather similar between these 5 species (see Tables 4 and 5). The new type of antenal chaetae discovered in this study (type 15) is found exclusively on the elongated antenna of T. spectabilis sp. nov. and T. takensis sp. nov. Troglopedetes rungsimae sp. nov., althought troglomorphic, has shorter antennae (873 µm) and, together with T. meridionalis and T. kae, does not present type 15 S-chaetae. This kind of chaetae was not detected in Coecobrya sirindhornae Jantarit, Satasook & Deharveng, 2019 and Lepidonella doveri (Carpenter, 1933), among the most troglomorphic Collembola regarding antennal elongation in Southeast Asia Jantarit et al. 2019). In Alloscopus Börner, 1906, Cyphoderus, Cyphoderopsis, and Rambusinella Deharveng & Bedos, 1996(Jantarit et al. 2013 Jantarit and Sangsiri 2020), we did not find this type 15 S-chaetae. Detailed analyses of antennal chaetae in other Entomobryoidea are lacking, and type 15 is so far a taxonspecific receptor limited to highly troglomorphic species of the genus Troglopedetes.

Ant. IVb
Length ( It seems that antennal phanerotaxy in the genus Troglopedetes is richer than in other Entomobryidae described so far. For example, 13 types of chaetae are reported in Alloscopus (Jantarit and Sangsiri 2020) and Cyphoderopsis (Jantarit et al. 2013), 12 types in Verhoeffiella (Lukić et al. 2015(Lukić et al. , 2018, at least 10 types in Lepidonella , and at least 12 types in Rambutsinella (unpublished data).
Generally, the length of antennal segments in Thai Troglopedetes ranked as Ant. IV (a+b) > II > III > I (Deharveng 1988a(Deharveng , 1990Deharveng and Gers 1993;, including T. multispinosus, which is second for antennal elongation in the genus in Thailand (ratio of antennae: body = 0.9). However, in the most troglomorphic species of the genus, T. spectabilis sp. nov., antennal segment length ranked as Ant. IV (a+b) > III > II > I. In T. takensis sp. nov. the length of Ant. II and III is a similar value and ranked as IV (a+b) > (II = III) > I. while T. rungsimae sp. nov. antennal segment length ranked as Ant. IV (a+b) > II > III > I. Hence, antennal length, which is a troglomorphic character, is not the result of a similar proportional increase of all antennal segments, as already observed in other cave species groups like Verhoeffiella (see Lukic et al. 2018).
According to the study of , the number of chaetae parallels the length of antennal segments only for the overall result and for ordinary chaetae, but not for S-chaetae. A similar conclusion can be drawn from this study (Tables 5 and 6). Ant. IV (a+b), the longest segment, carries less S-chaetae types (only 5-6 types) than other segments (Table 5). The distal subsegment of Ant. IV (Ant. IVb) has more kinds and a higher density of S-chaetae than the proximal one (Ant. IVa), although their relative length is subequal to equal . In this study, all three new species have Ant. IVa 1.25-1.4 times longer than Ant. IVb (Tables 1-3). However, in T. spectabilis sp. nov., Ant. IVa and Ant. IVb possesses a similar number of S-and ordinary chaetae, but T. takensis sp. nov. and T. rungsimae sp. nov. have more S-chaetae in Ant. IVb than Ant. IVa (Table 5). Type 10 and type 11 S-chaetae have a more complex arrangement and are more numerous in Ant. IV (a+b) than other segments. The number of type 10 S-chaeatae is higher in Ant. IVa ventrally, while type-11 is instead widespread in both dorsal and ventral sides of Ant. IVb in all described species (Table 5). Ordinary chaetae are normally more numerous in Ant. IVa than Ant. IVb because it is relatively longer than Ant. IVb, except in T. rungsimae sp. nov. where ordinary chaetae in Ant. IVb are significantly higher in number than Ant. IVa. On Ant. I, the shortest segment, the number of S-chaetae varies depending on species. In T. meridionalis and T. kae, Ant. I has more S-chaetae than Ant. II and III, while in T. spectabilis sp. nov., Ant. I has more S-chaetae than Ant. II only (Table 5). Conversely, T. takensis sp. nov. and T. rungsimae sp. nov. have less S-chaetae on Ant. I than on Ant. II and III. However, in all the described species, Ant.I is clearly richer than other segments in diversity of S-chaetae, with 7-8 S-chaetal types, emphasizing the importance for sensorial functions in this segment .
Ant. II is the second longest segment for the moderate long antennal species (T. rungsimae sp. nov. and also in T. meridionalis and T. kae), but it can be shorter than (T. spectabilis sp. nov.) or subequal to (T. takensis sp. nov.) Ant. III for the species with very long antennae. This segment has less S-chaetae than Ant. III (Table 5).
Ant. III is the second longest segment in species with very long antennae (T. spectabilis sp. nov., and T. takensis sp. nov.) and carries the highest number of S-chaetae after Ant. IV (Table 5). However, this segment ranks third in length for the moderately long-antenna species (T. rungsimae sp. nov., T. meridionalis and T. kae) and has a number of S-chaetae similar to Ant. II. Special to this segment is a group of S-chaetae of type 10 located latero-ventrally in the highly troglomorphic species (discussed below) and at the level of the antenna III organ (AIIIO). The AIIIO of the described species has at least 5 S-chaetae (one chaeta of type 1, two chaetae of type 4 and two chaetae of type 5, Figs 6C, D, 11C, 12D), like in T. kae and T. meridionalis. Two chaetae of type 4 are obviously sprinkled with pores. The AIIIO of Thai Troglopedetes is normally located apically in the latero-dorsal side of the antennae, except in T. spectabilis sp. nov. and T. takensis sp. nov. where it is obviously on the ventral side of the segment.
Meanwhile, the ventral side of the antennal segment possesses a higher number of chaetae than the dorsal one both in overall chaetae and S-chaetae (Table 4, [11][12][13]. This is probably because the targets of the sensorial receptors are more commonly found at ground level than above. Collembola antennae are also often raised and waved in the air (pers. observation), probably to pick up stimuli from objects and thus sensorial receptors on the ventral side may be more effective at detecting.
The diversity of antennal chaetae in Thai Troglopedetes does not differ significantly between the extremely long antennae and the moderately long antennae species. T. spectabilis sp. nov., the longest antennae species so far, has 21 types of chaetae (5 types of ordinary chaetae, 14 type of S-chaetae, a subapical organite and scale), whereas T. takensis sp. nov., T. rungsimae sp. nov. (long antennae) and T. kae (moderate long antennae) all have 20 types of chaetae (5 types of ordinary chaetae, 13 S-chaetal types, subapical organite and scale). Troglopedetes meridionalis (moderate long antennae) has 19 types of chaetae (5 types of ordinary chaetae, 12 S-chaetal types, subapical organite and scale) (Tables 4 and 5). It has long been known that antennal chaetae are associated with sensorial reception and cave adapted species are expected to sustain more numerous, larger or more diverse chaetae than surface species (Deharveng 1988b;Thibaud and Deharveng 1994;Lukić 2019). No increase in size or morphological diversity of chaetae has been observed in our species from more to less troglomorphic species. The only increase in sensorial potential is linked to the increase of chaetae number linked to the increase in size of antennae. However, the numerous non-cave species of the genus in Southeast Asia are still undescribed and have not been examined in this respect. More thorough studies therefore need to be done before drawing any conclusion, i.e. habitat preferences (cave vs. surface species), cave adaptation (troglomorphy vs. non-troglomorphy), sex (male vs. female) or life cycle (juvenile vs. adult). In any case, Troglopedetes is a good model to develop such investigations because of its large range of life styles (soil litter to cave) and morphological adaptations to the subterranean life.
Groups of subcylindrical S-chaetae (type 10) on antennal segments I, II and III deserve to be mentioned here. There are clusters of numerous S-chaetae in three Mediterranean cave species (T. ruffoi, T. absoloni and T. ildumensis) (Fanciulli et al. 2003;Soto-Adames et al. 2014; Table 6). This type of chaetae was detected in all the described Troglopedetes of Thailand and observed in several other undescribed species from soil and caves in the country. Among them all non troglomorphic species bear a small number of S-chaetae type 10 (<6) that are not grouped in clusters, but the two new elongated antennae species (T. spectabilis sp. nov. and T. takensis sp. nov.) show this cluster of S-chaetae type 10 on the ventral side of antennal segments I, II and III, constituting a large number of such chaetae than some of the Mediterranean species (Figs 5B, 6B, 6D, 11B, 12B, 12D, Tables 4-6). At this point, cluster of a high number of type 10 chaetae appears as a troglomorphic character in Troglopedetes species.
Although the function of individual chaetal types of Collembola antennae is little known, differences in the morphological structure of chaetae are likely to enable springtails to receive a wide range of different stimuli, responding to light, smell, taste, sound, touch, vibration, stretch, temperature, humidity, a multitude of chemical agents and concentration gradients of oxygen and carbon dioxide (Altner and Prillinger 1980;Hartenstein 1997;Hopkin 1997). We are convinced that the study of antennal chaetae in Collembola not only has important value for taxonomy, but would also bring a significant contribution in several areas for morphologists, physiologists and developmental biologists. From this perspective, ultrastructural data as a first insight into their functions are dramatically lacking.