The giant pill-millipede genus Zephronia Gray, 1832 from Thailand, with a redescription of Z.siamensis Hirst, 1907 and descriptions of three new species (Diplopoda, Sphaerotheriida, Zephroniidae)

Abstract Material of the giant pill-millipede genus Zephronia Gray, 1832 recently collected from Thailand contains three new species: Zephroniaenghoffisp. nov., Zephroniagolovatchisp. nov., and Zephroniapanhaisp. nov. The first Zephronia species recorded for Thailand, Z.siamensis Hirst, 1907, is also redescribed based on new specimens collected both from the type locality in Chonburi Province and from neighboring areas. Morphological characters of all new species, Z.phrain Likhitrakarn & Golovatch, 2021, and Z.siamensis are illustrated, and a distribution map of the confirmed Zephronia species occurring in Thailand is also provided.


Introduction
One of the remarkable diplopod groups, the giant pill-millipede genus Zephronia Gray, 1832 is one of the most speciose not only in the family Zephroniidae, but also in the entire order Sphaerotheriida. It currently contains 44 described species ranging from the Himalayas of India in the west, to mainland Southeast Asia in the east (Wesener 2016(Wesener , 2019. Although several species have been revised and new species described from a number of areas in Asia, e.g., Myanmar, Northeast India, and Vietnam, Zephronia diversity still remains understudied in many other countries, e.g., Cambodia, Laos, and Thailand. Thailand is located within one of the global hotspots of biodiversity (Indo-Burma) (Clements et al. 2006), and even though recent progress in revealing its diplopod fauna is considerable, especially as regards the orders Spirobolida, Spirostreptida, and Polydesmida. (Pimvichai et al. 2009(Pimvichai et al. , 2010Likhitrakarn et al. 2011Likhitrakarn et al. , 2014Srisonchai et al. 2018a, b), only four species of Zephronia have hitherto been reported from Thailand. These are as follows: Z. siamensis Hirst, 1907, Z. lannaensis Likhitrakarn & Golovatch, 2021, Z. phrain Likhitrakarn & Golovatch, 2021, and Z. viridisoma Rosenmejer & Wesener, 2021. Recent intense collecting efforts made by Thai specialists in collaboration with the Department of National Parks, Wildlife and Plant Conservation across the country have revealed numerous interesting millipedes, especially in limestone areas. From these efforts, several new genera and numerous new species have been recorded and described (Pimvichai et al. 2018(Pimvichai et al. , 2020Srisonchai et al. 2018a, b, c, d;Likhitrakarn et al. 2020Likhitrakarn et al. , 2021. The present contribution provides descriptions of three new species of the genus Zephronia, as well as a redescription of Z. siamensis Hirst, 1907 as based both on topotypes and near-topotypes.

Specimen collection and preservation
The millipedes were collected by active search in daytime during the field trips in Thailand. All material was collected by ASRU (Animal Systematics Research Unit) members. Live specimens of both sexes were photographed with a Nikon D700 camera equipped with a AF-S VR Micro-Nikkor 105 mm lens. Specimens were then euthanized based on the methods of AVMA guidelines for the euthanasia of animals (American Veterinary Medical Association 2020) with a permission of the Animal Care and Use. Most of the specimens were stored in 70% ethanol for morphological examination. Latitude, longitude, and elevation were recorded using a Garmin GPSMAP 60 CSx at the field sites, and all coordinates of the precise locations were mapped with Google Earth.

Morphological study, description, and illustrations
All morphological characters were analyzed under a NIKON SMZ-445 stereo microscope. For Scanning Electron Microscopy (SEM), the specimens were mounted on aluminum stubs, coated with pure gold and studied using a JOEL JSM-6610LV scanning electron microscope. The descriptions are applied to both males and females. Species delimitation and morphological descriptions were based on Wesener and Sierwald (2005), Wesener (2016Wesener ( , 2019, Semenyuk et al. (2018Semenyuk et al. ( , 2020 and Likhitrakarn et al. (2021). Illustrations of external morphological characters were sketched from one view, whereas the telopods were depicted from three sides (anterior, posterior, and lateral views) under the stereo microscope and all were modified using Adobe Photoshop CS6 software in order to generate plates of figures.

Depositions of holotypes, paratypes, and other new specimens
All material of each species is referred to each species description. The holotypes are deposited in the Chulalongkorn University Museum of Zoology (CUMZ, CUMZ-Zeph0005-0010) and some paratypes are shared with three other museums including the Natural History Museum of Denmark, University of Copenhagen, Denmark (NHMD), the Zoological Museum, State University of Moscow, Russia (ZMUM), and the Zoological Reference Collection of the Lee Kong Chian Natural History Museum, Singapore (ZRC).

Acronyms used in the descriptions
cp cuticular impression cr-T crenulated teeth cx coxa is inner section ML membranous lobe ms middle section o operculum of vulva ot outer section pm posterior margin pre prefemur sp sclerotized process st-pl stigmatic plate syn-cx syncoxite
above sea-level ca.
about, around, circa CUMZ Chulalongkorn University Museum of Zoology, Thailand Koh the Thai word for "island" NHMD Natural History Museum of Denmark, University of Copenhagen, Denmark Wat the Thai word for "temple" ZMUM Zoological Museum, State University of Moscow, Russia.

Positional and directional terms used in the descriptions
See the details in species descriptions by Wesener (2019), Likhitrakarn et al. (2021), and also some definitions in Srisonchai et al. (2018a, b).
Diagnosis. A member of Zephronia s. s. in which the position of Tömösváry's organ located next to the aberrant ommatidia, not inside the antennal groove. Adult body length relatively small, usually ca. 20 mm, < 26.5 mm, tip of subanal plate con- cave, process of telopoditomere 2 of anterior telopod rather short and strongly curved distally, and process of telopoditomere 2 of anterior telopod shorter than the combination of telopoditomeres 3 and 4. Similar in these respects to Z. laotica Wesener, 2019  and Z. dawydoffi Attems, 1953. Differs from these two species by showing a body length > 16.7 mm, live specimens with unique dark green, tergites with two yellowbrown patches located in anterior half of tergites, surface of tergites with conspicuous setae, femur of leg extended with conspicuous teeth, and telopoditomere 4 of anterior telopods posteriorly with a row of conspicuous crenulated teeth (cr-T).
Color : Live specimens dark green; antennae dark brown; head, collum, thoracic shield, paratergites brown; legs bluish green. Tergites with two big patches, brown or yellowish brown, arranged in almost central part of anterior half; lateral part of tergites greenish dark, middle part of tergites brown. Anal shield with two colors contrasting each other, posterior half reddish brown, anterior half greenish dark brown. Color in alcohol after three months of preservation changed to greenish brown, head and collum dark greenish, tergites with a dark posterior margin, legs pale yellowish, distal podomeres rusty brown, antennae dark green.
Head: Trapezoid, anterior part of head clothed with numerous long setae, posterior part sparsely punctate; anterior margin of labrum with a single tooth. Each eye with 75-92 ommatidia. Aberrant ocellus located inside antennal groove.
Tömösváry's organ: Located separately at a small, projected brim between ommatidia and antennal socket.
Gnathochilarium: Ventral surface with setae, other structures typical of the order. Palpi with sensory cones arranged in clusters. Mandibles not dissected.
Laterotergites: 1 and 2 with a broad and well-rounded projection. Collum: With glabrous surface, sparsely setose with very long setae, except for anterior and posterior margins which are densely setose.
Thoracic shield: Surface with tiny setae as on tergites. Shallow grooves filled with numerous long setae, no keels. Tergites ( Fig. 1A-C): Surface shining, entirely clothed with dense and tiny setae, each seta located in a tiny pit. Tip of paratergites weakly projecting posteriorly.
Endotergum (Figs 13A, B, 14A): Posterior margin with lobes, 'rectangle-wavy' margin. Inner section (inner area) smooth, with a few setae. Middle section (middle area) with a single row of conspicuous, elliptical cuticular impressions; distance between impressions as wide as individual diameter. Bristles arranged in one row, tip of the longest bristles not extended beyond posterior margin or not reaching to posterior margin.
Anterior telopods : First telopoditomere rectangular, slightly longer than wide. Telopoditomere 2 large, as long as telopoditomeres 3 and 4 combined. Process of telopoditomere 2 located posteriorly, but partly visible laterally in anterior view. Process of telopoditomere 2 wide, broader than telopoditomeres 3 and 4. Process of telopoditomere 2 conspicuously unciform, protruding as high as basal part of telopoditomere 4, apically with a well-rounded tip. Margin towards telopoditomere 3 with a membranous area carrying a rather small and sclerotized process (sp), apically with a rounded tip. Telopoditomere 3 slender, 1.4X longer than wide, 1.5X longer than telopoditomere 4. Telopoditomere 4 posteriorly with a row of 7 small and crenulated teeth (cr-T) with two prominent spines. All podomeres covered with long sparse setae, except for central part of telopoditomere 1 and posterior surfaces of 2-4.
Posterior telopods (Fig. 4D-F): Inner horns with sharply edged tips, slightly curved caudad. Telopodite consisting of four podomeres. First podomere stout and narrow, nearly twice as wide as long. Immovable finger (process of telopoditomere 2) shorter than movable finger (consisting of telopoditomeres 3 and 4). Immovable finger stout and narrow, 1.6X longer than wide, not curved, glabrous distally. Margin towards movable finger with two massive, triangular, membranous lobes (ML). Telopoditomere 3 elongated, slightly curved, twice as long as telopoditomere 4; with a large, swollen, membranous ledge; postero-apically slightly enlarged, with a row of 11 or 12 crenulated teeth (cr-T). Telopoditomere 4 slender, twice as long as wide, slightly tapering apically; with a large, swollen, membranous ledge; with two long and sclerotized spines. Telopoditomeres 1 and 2 on both sides covered with few setae. Telopoditomere 3 at base of inner margin with a few setae, remaining parts of telopoditomeres 3 and 4 almost glabrous.
Distribution and habitats (Figs 15A,16). The newly collected specimens from the type locality were found under groups of Pandanus trees in a limestone area near a beach, while the other material from the Chonburi and Rayong provinces were likewise taken from limestone habitats. Currently, this species is known to occur only in eastern Thailand.
Remarks. The live coloration of adults is generally dark green with two yellowish brown patches in the anterior half of tergites, this being quite unique for this species.
Almost 114 years since the original description, a redescription of Z. siamensis Hirst, 1907 has been made in this study based on the newly collected specimens from Koh Srichang (Srichang Island), here regarded as strict topotypes.
Considerable variation has been found in body size of the specimen described by Hirst (1907) compared to the topotypes: the type specimen was ca. 26.5 mm in length, whereas the new material we examined were within the size range of 16.7-23.5 mm.

Zephronia phrain Likhitrakarn & Golovatch, 2021
Color (Fig. 1E, F): Specimens in life with brown or dark brown; head, antennae and collum, thoracic shield, paratergites, anal shield and legs brown or dark brown; anterior margins of thoracic shield, of tergites and of anal shield dark brown contrasting with the posterior brown ones; setose part of thoracic shield with golden sheen. Color in alcohol after six years not changed.
Distribution and habitats (Figs 15D,16). Currently known to occur in northern Thailand (Chiang Mai and Tak provinces) in dry dipterocarp forest and from limestone areas. Observations made at Phawor Shrine found that most specimens were seen creeping on rocks, with some hiding in leaf litter. Notably, the specimens were found in syntopy with the dragon millipede (Nagaxytes spatula Srisonchai, Enghoff & Panha, 2018) at the same site (Srisonchai et al. 2018b).
Remarks. Based on observations of live specimens in the field, two color patterns were found, dark green in type specimens and brown/dark brown in the others from Tak Province ( A species described by Pocock (1890) from Myanmar (Thagatà, Mount Mooleyit, Kayah State), Z. gestri Pocock, 1890 occurs close to the type locality of this widespread species, but Z. phrain clearly differs from Z. gestri by being longer in body length (vs. shorter, ca. 14 mm), having a longer immovable finger or longer process of telopoditomere 2 (vs. shorter) and having a truncate/round central margin of subanal plate (vs. convex).
Remarks. Only nine specimens have been collected and all were found to appear in a small area. This species can be regarded as endemic to southern Thailand.  Etymology. This species is named after Henrik Enghoff from Natural History Museum of Denmark, University of Copenhagen, Denmark, the Danish myriapodologist who initiated an important research step on millipede studies for Thailand.
Diagnosis. A member of Zephronia s. s. in which the position of Tömösváry's organ located next to the aberrant ommatidia, not inside the antennal groove. Adult body length medium, > 29 mm, usually ca. 32 mm, up to 36 mm; body brown or dark brown, inner surface (underside) of anal shield with a single locking carina on each side, and leg-pair 2 of male coxa with a long membranous lobe at mesal margin. Similar in these respects to Z. golovatchi sp. nov., but differs from this species by the following combination of characters; antenna short, leg-pair 2 of female coxa apico-mesally with large and conspicuous coxal ridge, operculum of vulva regularly rounded and narrow in posterior view, mesal margin of operculum tapering apically, central margin (tip) of subanal plate shallowly concave, process of telopoditomere 2 of anterior telopod quite long and equal in length to the combination of telopoditomeres 3+4, and immovable finger telopoditomere 2 of posterior telopod (process of telopoditomere 2) equal in length to movable finger (consisting of telopoditomeres 3 and 4).
Body Color ( Fig. 2A, B): Specimens in life with light brown to brown color; antennae dark brown; head, thoracic shield, tergites, paratergites and basal part of legs brown; posterior margin of tergites dark brown; a few apical podomeres greenish brown. Color in alcohol after 8 months not changed.
Head: Wide and stout, subtrapeziform; anterior part of head with dense and long setae; central part of head glabrous; posterior part of head with dense and short setae. Labrum with a single tooth at anterior margin. Each eye with 90-100 ommatidia. Aberrant ocellus located near antennal groove (at upper part of groove).
Tömösváry's organ: Separated from ommatidium, located on a brim between ommatidia and antennal socket, smaller in diameter than an individual ommatidium.
Gnathochilarium: Ventral surface with setae, other structures typical of the order. Mandibles not dissected.
Collum: Surface glabrous, except for anterior margins near rim with isolated and long setae.
Thoracic shield: Surface as those of tergites, covered with small setae, each seta located in a tiny pit; shallow groove wide anterolaterally, with very long setae.
Endotergum (Figs 13C,D,14B): Posterior margin flat, regular. Inner section (inner area) with setiferous tubercles or setae. Middle section (middle area) with a single row of elliptical cuticular impressions, distance between impressions longer than in-dividual diameter. Bristles arranged in two rows, tip of the longest bristles extended beyond posterior margin or reaching to posterior margin.
Anal shield: Sexually dimorphic, in female very large and strongly rounded, in male slightly more rectangular. Outer surface covered by tiny and dense setae locating in small pits, similar to those of tergites. Inner surface (underside) covered by long setae; with a single, black, and long locking carina, half as long as length of last laterotergite.
Anterior telopods (Fig. 8A, B, D): Telopodite with four telopoditomeres; all telopoditomeres sparsely setose, except for the apical part of telopoditomere 3 and all parts of telopoditomere 4 without setae. First telopoditomere rectangular, slightly large and stout, broader than telopoditomeres 2-4. Telopoditomere 2 large. Process of telopoditomere 2 equal in length to the combination of telopoditomeres 3 and 4; visible in posterior view; curved and slender, 1.5X longer than wide, twice as long as telopoditomere 4; tip bent and round, directed anteriad, close to the basal part of telopoditomere 4. Margin towards telopoditomere 3 with a membranous area carrying a sclerotized process (sp), conspicuous, short, apically with sharp tip. Telopoditomere 3 with six small crenulated teeth (cr-T) in ventral side. Telopoditomere 4 short and stout, conspicuous, straight; tip round, directed mesad; with two prominent sclerotized spines in posterior side.
Posterior telopods (Fig. 8A, C, D): Telopodite with four telopoditomeres; telopoditomeres 1 and 2 on both sides covered with sparse setae, except for immovable finger part; telopoditomere 3 at base of both inner margin and outer margin with a few setae; telopoditomere 4 without setae. First telopoditomere stout and broad, half as long as telopoditomere 2. Telopoditomere 2 slender, immovable finger (process of telopoditomere 2) as long as movable finger (consisting of telopoditomeres 3 and 4). Immovable finger long and slender, wide, 2.5× as long as wide, not curved, tip directed mesad; at margin with several semi-circular rows of sclerotized spots. Margin towards movable finger with two conspicuous membranous lobes, triangular, inner lobe bigger and longer than outer one. Telopoditomere 3 slender, quite long, slightly expanded distad, slightly curved, thrice as long as telopoditomere 4; with a long and sclerotized spine located on a large, swollen, membranous lobe; posterior part with a row of 17-19 crenulated teeth (cr-T). Telopoditomere 4 short and stout, 1.5× longer than wide; at inner margin with a large, conspicuous, swollen, membranous lobe and two evident sclerotized spines.
Distribution and habitats (Figs 15B, C, 16). All specimens were collected from limestone habitats (in dry dipterocarp forest). Known only from three sites in limestone mountain ranges of Khon Kaen and Loei provinces.
Remarks. With regard to the morphological characters of coxae 2 in both male and female, this species exhibits the remarkable shape in which the male has a very long membranous lobe (Fig. 7D) and the female displays conspicuous coxal ridges apico-mesally (Fig. 7E). Moreover, the surface of tergites covered with conspicuous setae/hairy in Z. enghoffi sp. nov. is more distinctive than in the other two new species ( Fig. 2A, B). Etymology. The species is named for our highly esteemed colleague Sergei I. Golovatch (Zoological Museum, State University of Moscow, Russia), one of the most productive millipede taxonomists, who encouraged all new and young myriapodologists in Thailand.
Diagnosis. Adult body length medium to large > 29 mm, usually 35 mm, up to 37 mm; body brown or dark brown, marginal bristles of endotergum extending over posterior margin, inner surface (underside) of anal shield with a single locking carina on each side, and leg-pair 2 of male coxa with membranous lobe at mesal margin. Similar in these respects to Z. enghoffi sp. nov., but differs from this species by the following combination of characters: antenna long; operculum of vulva regularly rounded and broad in posterior view; mesal margin of operculum not tapering apically; central margin (tip) of subanal plate divided by a conspicuous mesal constriction, process of telopoditomere 2 of anterior telopods shorter than telopoditomere 3; telopoditomere 3 of anterior telopods with 2 or 3 crenulated teeth; immovable finger telopoditomere Body height: Height in male ca 11.0 mm (holotype 11.0 mm), female 11.0-12.0 mm; thoracic shield 9.0-10.5 mm; tergite 10.0-11.5 mm.
Color (Fig. 2C, D): Specimens in life with brown color; antennae dark brown; head, collum, thoracic shield, tergites, paratergites, anal shield and legs brown; posterior margin of tergites dark brown. Color in alcohol after 13 years changed to pale brown.
Head: Wide and stout, subtrapeziform; anterior part of head with dense and long setae; central part of head with sparse and long setae; posterior part of head with dense and short setae. Labrum with a single tooth at anterior margin. Each eye with ca. 90-100 ommatidia. Aberrant ocellus located inside antennal groove (at upper part of groove).
Tömösváry's organ: Not distinctly separated from ommatidium, located closely to anterior margin of ommatidia, equal in size to an individual ommatidium.
Gnathochilarium: Ventral surface with setae, other structures typical of the order. Mandibles not dissected.
Collum: Surface glabrous, except for anterior margins near rim with isolated and long setae.
Thoracic shield: Surface as those of tergites, covered with inconspicuous and small setae, each seta located in tiny pits; shallow groove wide anterolaterally, with very long setae.
Endotergum (Figs 13E,F,14C): Posterior margin flat, regular. Inner section (inner area) with a few setiferous tubercles or setae. Middle section (middle area) with a single row of small, conspicuous, elliptical cuticular impressions; distance between impressions longer than individual diameter; with a row of conspicuous ridges between bristles and impressions. Bristles arranged in two rows, tip of the longest bristles extended beyond posterior margin or reaching to posterior margin.
Posterior telopods (Fig. 10A, C, D): Telopodite with four telopoditomeres; telopoditomeres 1 and 2 on both sides sparse setose, except for apical part of immovable finger (process of telopoditomere 2); telopoditomere 3 at base of inner margin with conspicuous setae, but none for outer margin; telopoditomere 4 without setae. First telopoditomere large, wide, as long as wide. Telopoditomere 2 large, immovable finger (process of telopoditomere 2) relatively shorter than movable finger (consisting of telopoditomeres 3 and 4). Immovable finger slender, twice as long as wide, slightly curved, tip directed anteroventrad; at margin with several semi-circular rows of sclerotized spots, conspicuous. Margin towards movable finger with two membranous lobes, conspicuous and long, conical, inner lobe bigger and longer than outer one, tip sharp. Telopoditomere 3 very long and slender, tapering apically, strongly curved, thrice as long as telopoditomere 4; with a long and sclerotized spine located on a large, swollen, membranous lobe; posterior part with a row of 17 or 18 crenulated teeth (cr-T). Telopoditomere 4 slender, 2× longer than wide; at inner margin with a large, conspicuous, swollen, membranous lobe and with two evident sclerotized spines; tip curving mesodorsad.
Distribution and habitats (Fig. 16). Known only from the type locality. All specimens have been taken from limestone habitats and were found walking on top of decayed wood or hiding under leaf litter.
Remarks. This species has thin membranous lobe on male coxae 2 (Fig. 9D), but this lobe seems to be shorter than that of Z. enghoffi sp. nov. (Fig. 7D). Etymology. The species name recognizes the great professor and a long-time mentor to the authors, Somsak Panha (Chulalongkorn University Museum of Zoology, Thailand).
Diagnosis. Differs from all congeners by the combination of the following characters; grey body color, adult body length ca. 21 mm, tergites covered by conspicuous setae, long setae on tergites extending over the posterior margin (Figs 13G, 14D), marginal bristles of endotergum not extending over posterior margin, margin of operculum on vulva slightly concave and slightly invaginated medially, telopoditomere 3 of anterior telopods with conspicuous crenulated teeth and telopoditomere 3 of posterior telopods with a row of 11or 12 crenulated teeth.
Color (Fig. 2E, F): Specimens in life with light grey; head, antennae and collum greenish grey; thoracic shield, tergites and anterior part of anal shield grey; paratergites, posterior margins of tergites and posterior part of anal shield greyish brown. Color in alcohol after two years not changed.
Head: Wide and stout, subtrapeziform; anterior part of head with dense and long setae; central part of head with sparse and long setae; posterior part of head with dense and short setae. Labrum with a single tooth at anterior margin. Each eye with ca. 70 ommatidia. Aberrant ocellus located near antennal groove (at upper part of groove).
Laterotergites: Laterotergites 1 and 2 narrow, projecting to a sharp tip. Collum: Surface with very long setae in both anterior and posterior margins, setae located in pits.
Thoracic shield: Surface as those of tergites, covered with tiny setae; shallow groove with long setae, slightly broad at anterolateral margin.
Endotergum (Figs 13G,H,14D,E): Posterior margin flat, regular; tip of setae. Inner section (inner area) with a few setiferous tubercles or setae. Middle section (middle area) with a single row of conspicuous, elliptical cuticular impressions; distance between im- pressions longer than individual diameter. Bristles arranged in two rows, tip of the longest bristles not extended beyond posterior margin or not reaching to posterior margin.
Anal shield: Sexually dimorphic, in female weakly bell-shaped, in male strongly bell-shaped. Outer surface pubescent, setae small and very short, similar to those of tergites. Inner surface (underside) covered by setae; with a single locking carina, half as long as length of last laterotergite.
Posterior telopods (Fig. 12A, C, D): Telopodite with four telopoditomeres; telopoditomeres 1 and 2 on both sides with sparse setae, except for apical part of immovable finger (process of telopoditomere 2); telopoditomere 3 at base of inner margin with conspicuous setae, but none for outer margin; telopoditomere 4 without setae. First telopoditomere stout and narrow, ca. half as long as telopoditomere 2. Telopoditomere 2 large, immovable finger (process of telopoditomere 2) relatively shorter than movable finger (consisting of telopoditomeres 3 and 4). Immovable finger slender, twice as long as wide, strongly curved, tip directed anteroventrad; at margin with several conspicuous semi-circular rows of sclerotized spots. Margin towards movable finger with two membranous lobes, conspicuous long, triangular, inner lobe bigger and longer than outer one, tip sharp. Telopoditomere 3 very long and slender, tapering apically, curved, thrice as long as telopoditomere 4; with a long and sclerotized spine located on a large, swollen, membranous lobe; posterior part with a row of 11-12 crenulated teeth (cr-T). Telopoditomere 4 slender, 2× longer than wide; at inner margin with a large, conspicuous, swollen, membranous lobe and with two evident sclerotized spines; tip curving mesad.
Distribution and habitats (Fig. 16). The new species is known from Phetchaburi, Ratchaburi, and Kanchanaburi provinces. All specimens were collected from limestone habitats. Remarks. At the field collecting site, grey living specimens blended in perfectly with the brownish grey rock or leaf litter, making it difficult to find the animals. All specimens were infested by tiny, engorged, white, phoretic deutonymphs of an unidentified mite. The mite can often be found especially on the ventral part of the body such as antennal sockets and coxae, and could easily be discerned. The distribution of Z. viridescens from Dawei, Myanmar (Tavoy, Lower Burma -Moti Ram), is quite close to where the new species is distributed. However, Z. panhai sp. nov. differs from it by having a shorter body length ca. 21 mm (vs. longer, ca. 32 mm) and telopoditomeres 3 and 4 of anterior telopod distinctly separated (vs. indistinctly separated).

Unconfirmed species recorded for Thailand
Zephronia cf. viridescens Attems, 1936 Zephronia viridescens Attems, 1936: 180;Jeekel 2001 (2015) have reported 'Zephronia cf. viridescens' from northern and northeastern Thailand, these works do not provide clear and unique characters for the species, and the specimens are not available for re-examination. The original description by Attems (1936) clearly stated that one of the diagnostic characters of Z. viridescens is its greenish body color. These contrast with the 'viridescens' material examined by Wongthamwanich et al. (2012b: fig. 4) and Sukteeka and Thanee (2015: fig. 2), which display a distinct brownish body color. Not only can the brown color be used to discriminate Z. viridescens from Thai 'viridescens' material, but the distribution is remarkably different. Z. viridescens was originally described from Dawei in Myanmar while 'viridescens' specimens have been recorded to inhabit the northern and northeastern regions of Thailand. It seems likely that the 'viridescens' specimens belong to another species and are distinct from all other known species. Therefore, further systematics study based on fresh specimens from northern and northeastern Thailand is necessary in order to confirm the existence of Z. viridescens in Thailand. At this moment, we thus exclude this nominal species from the Thai millipedes.

Discussion
The exploration of the millipede fauna in Thailand has uncovered a hitherto unknown diversity among the genus Zephronia. With the three new species described herein, the Thai giant pill-millipede genus Zephronia currently contains seven species that promote the number in the genus to 47 species in total. Considering the recorded species of Zephronia in Thailand, all can be found in small distribution area, although two of them (Z. panhai sp. nov. and Z. siamensis) have been shown to have somewhat wider ranges. However, they still occupy less than approximately 300 km 2 along the mountain ranges in the North and also gulf of Thailand in the East (Fig. 16). This pattern is also marked in Sphaerobelum species (S. aesculus Rosenmejer & Wesener, 2021(Rosenmejer et al. 2021)) by its occurrence at 160 km east of the type locality. The species boundaries of Zephronia have been mostly based on several morphological features (Wongthamwanich et al. 2012a;Semenyuk et al. 2018;Wesener 2019). The most distinctive characteristics of the three species compared to the congeners can be seen especially in endoterga, anterior telopod and posterior telopod. The use of combinations of characters as being utilities for species discrimination in this study is congruent with previous taxonomic works (Golovatch et al. 2012;Wesener 2016Wesener , 2019Semenyuk et al. 2018Semenyuk et al. , 2020Likhitrakarn et al. 2021). Furthermore, based on the observations in the field, the live specimens of some species can be easily distinguished from other congeners by their bright body color as presented in Z. panhai sp. nov. (Fig. 2E, F), Z. phrain (Fig. 1E, F) as well as in Z. siamensis (Fig. 1A-D). Based on the combination of several morphological traits plus the live body color, we can confirm that the species boundaries are within Zephronia.
As the two recognized groups of Zephronia have been proposed based on the location of Tömösváry's organ (Wesener 2019;Semenyuk et al. 2020;Likhitrakarn et al. 2021), the three new species exhibit all of the unique characters that are in agreement with its placement in Zephronia s. s. The group previously harbored nine species, viz., Z. dawydoffi Attems, 1953, Z. konkakinhensis Semenyuk et al., 2020, Z. lannaensis Likhitrakarn & Golovatch, 2021, Z. montis Semenyuk et al., 2020, Z. ovalis Gray, 1832, Z. phrain Likhitrakarn & Golovatch, 2021, Z. siamensis Hirst, 1907, Z. viridescens Attems, 1936, and Z. viridisoma Rosenmejer & Wesener, 2021. Unfortunately, the lack of genetic data prevents a conclusive phylogenetic comparison to other closely related species of the genus at this point. It will be necessary to continue with studies on this group, collecting new material as well as re-examining previously collected material in combination with molecular works. In this way, the systematics within the genus or closely related genera may be elucidated and improved.
The preceding records of the genus, without regarding the three newly described species, were recorded only from northern and eastern parts of Thailand. The central and southern areas of Thailand, which are the intermediate zone between the Malay Peninsula and the upper region of mainland Southeast Asia, had no records of the genus so far. Our finding of these three species fills the gaps in the distribution and confirms the genus Zephronia across Thailand. Further collecting in unexplored areas in several parts of mainland Southeast Asia, especially Cambodia, Laos, and Thailand, will probably reveal many new, remarkable species.