Research Article
Research Article
A new jewel-like species of the pill-millipede genus Sphaerobelum Verhoeff, 1924 (Diplopoda, Sphaerotheriida, Zephroniidae) from Thailand
expand article infoRuttapon Srisonchai, Natdanai Likhitrakarn§, Chirasak Sutcharit|, Thierry Backeljau#, Piyatida Pimvichai¤
‡ Khon Kaen University, Khon Kaen, Thailand
§ Maejo University, Chiang Mai, Thailand
| Chulalongkorn University, Bangkok, Thailand
¶ Royal Belgian Institute of Natural Sciences, Brussels, Belgium
# University of Antwerp, Antwerp, Belgium
¤ Mahasarakham University, Maha Sarakham, Thailand
Open Access


A new species of the giant pill millipede genus Sphaerobelum is described: Sphaerobelum turcosa sp. nov. from the northeastern part of Thailand. Species delimitation is based on morphological characters and COI sequence data. The new species can be clearly discriminated from congeners by its greenish-blue body color, the face mask-like appearance of the thoracic and anal shields jointly when rolled up, and the combination of the following four characters: (1) the coxa of the second leg laterally with a sharp and long process, (2) the tarsi of legs 4–21 with 6–7 ventral spines, (3) the anterior telopods consisting of four conspicuous telopoditomeres, and (4) the immovable, slender (not strongly humped) and distally curved finger of the posterior telopods without a membranous spot. The interspecific COI sequence divergence between the new species and other Sphaerobelum species ranges from 17% to 23% (mean 20%). The intergeneric COI sequence divergence between the new species and Zephronia species ranges from 18% to 21% (mean 20%). The relationships among Sphaerobelum and Zephronia species based on the COI sequence data were not resolved in this study. Sphaerobelum turcosa sp. nov. is restricted to limestone habitat in Loei province and is probably endemic for the Thai fauna.

Key words

Biodiversity, limestone karst, soil fauna, Southeast Asia, taxonomy


Limestone karsts in Southeast Asia are referred to as ‘arks of biodiversity’ and as such are a priority for biodiversity conservation (Clements et al. 2006). Karst hills usually are relatively small, scattered and isolated, but nonetheless may support large numbers of endemic organisms (Schilthuizen 2011; Tolentino et al. 2020), including a wide variety of millipede species (Golovatch 2015; Liu et al. 2017; Liu and Wynne 2019).

The recent checklist of the millipedes (Diplopoda) of Thailand revealed 263 species. Of these, 222 species (84%) occur only in Thailand and are thus supposed to be endemic (Enghoff 2005; Likhitrakarn et al. 2023). The majority of Thai endemic millipede taxa exclusively inhabit limestone areas and habitats, e.g., Plusioglyphiulus Silvestri, 1923 (Golovatch et al. 2011a), Glyphiulus Gervais, 1847 (Golovatch et al. 2011b), Orthomorpha Bollman, 1893 (Likhitrakarn et al. 2011), Desmoxytes Chamberlin, 1923 (Srisonchai et al. 2018) and Coxobolellus Pimvichai et al., 2020 (Pimvichai et al. 2020).

Recent fieldwork conducted in the impressive geological landscape at Phu Pha Lom Forest Park, Loei Province in the northeastern part of Thailand, has unveiled remarkable greenish-blue specimens of a giant pill-millipede which clearly belongs to the family Zephroniidae in the order Sphaerotheriida. Recently, the species diversity of this family in Thailand has gained considerable attention (Likhitrakarn et al. 2021; Rosenmejer et al. 2021; Srisonchai et al. 2021; Bhansali and Wesener 2022). The updated records for Zephroniidae in Thailand contains only two genera with a total of 12 valid species (see Likhitrakarn et al. 2023). The number of species, however, is still lower than in some surrounding countries, e.g., Laos, Vietnam and India (Wesener 2019; Semenyuk et al. 2020).

The external characteristics place the specimens within the genus Sphaerobelum and the present contribution aims at providing the formal description of this new Sphaerobelum species based on morphological and DNA data.

Materials and methods

Sample collections

Specimens were hand-collected from limestone habitats in Phu Pha Lom Forest Park, Loei Province, Thailand, by visual spotting on open surfaces in daylight. Photographs of live animals were taken with a Canon 70D digital camera with a Canon EF-S 60 mm f/2.8 Macro USM lens. The specimens were euthanized based on AVMA guidelines for the euthanasia of animals (American Veterinary Medical Association 2020), and then preserved in 75% ethanol for morphological study and 95% ethanol for DNA sequence analysis.

The collecting sites were located by GPS using a Garmin GPSMAP 60 CSx, and all coordinates and elevations were rechecked with Google Earth. The background of the distribution map was downloaded from Elastic Terrain Map ( (Willett et al. 2015) and the figure was composed using Adobe Photoshop CS6.

This research was conducted under the approval of the Animal Care and Use Committee (Protocol Reviews No. IACUC-KKU-136/64 from Khon Kaen University) and No. 1723018 from Chulalongkorn University.

Morphological study

The specimens were examined and measured under a Nikon SMZ 745T trinocular stereo microscope, equipped with a Canon EOS 5DS R digital SLR camera. For scanning electron microscopy (SEM), the specimens were photographed with a JEOL, JSM-5410 LV microscope using gold-coated samples. Line drawings were based on photographs taken under the stereo microscope equipped with a digital SLR camera. All final images were processed and edited with Adobe Photoshop CS6.

The terminology of morphological descriptions follows Wesener and Sierwald (2005), Wongthamwanich et al. (2012), Wesener (2016, 2019) and Semenyuk et al. (2018, 2020).

The holotypes, as well as most of the paratypes are housed in the Museum of Zoology, Chulalongkorn University (CUMZ), Bangkok, Thailand.

The following abbreviations are used in the figures: Cx = coxa, cp = cuticular impression, ia = inner area, ma = middle area, o = operculum of vulva, oa = outer area, pm = posterior margin, Pre = prefemur, St-Pl = stigmatic plate, Syn-Cx = syncoxite.

DNA extraction and phylogenetic study

Total genomic DNA was extracted from legs using the NucleoSpin Tissue kit following the manufacturer’s instructions. PCR amplifications and sequencing of the standard mitochondrial COI DNA barcoding fragment (Hebert et al. 2003) were done as described by Pimvichai et al. (2020). The COI fragment was amplified with the primers LCO-1490 and HCO-2198 (Folmer et al. 1994). The new COI nucleotide sequences have been deposited in GenBank under accession numbers OR530087OR530089. Sample data and voucher codes are provided in Table 1.

Table 1.

Specimens from which the COI gene fragment was analysed. CUMZ (Museum of Zoology, Chulalongkorn University, Bangkok, Thailand); MHNG (Muséum d’Histoire Naturelle de la Ville de Genève, Geneva, Switzerland); MS (Tokyo Metropolitan University Collection, Tokyo, Japan); NHMD (Natural History Museum of Denmark); SCAU (South China Agricultural University, Guangdong, China); SMF (Senckenberg Museum Frankfurt, Germany); ZFMK (Zoological Research Museum Koenig, Bonn, Germany); ZMUC (Zoologisk Museum, University of Copenhagen, Denmark). Abbreviations after species names refer to the isolate of each sequence. GenBank accession numbers are indicated for each species.

Species Voucher code COI accession numbers Locality References
Order Sphaerotheriida
Family Zephroniidae Gray, 1843
Genus Sphaerobelum Verhoeff, 1924
S. aesculus NHMD 621694 MW898738 Thailand, Nakhon Si Thammarat Province, Khao Luang NP Rosenmejer et al. 2021
S. benquii SCAU MMY01 OP339792 China, Guizhou, Tongren City, Jiangkou County, Guanhe Town, Guanhe Village, Maomaoyan Zhao et al. 2022
S. bolavensis MHNG LT-10/24 MK330982 Laos, Champasak Province, Bolaven Plateau, 3 km S of Ban Nong Luang, Tad Kameud Wesener 2019
S. denticulatum MHNG MK330984 Laos, Oudomxai Province, ca 3 km E of Tad Lak 11, SE of Oudomxai city Wesener 2019
S. huzhengkuni SCAU SP03 MT657328 China, Guizhou Province, Tongren City, Fanjingshan National Nature Reserve Zhao et al. 2020
S. lachneeis MHNG MK330983 Laos, Oudomxai Province, ca 3 km E of Tad Lak 11, SE of Oudomxai city Wesener 2019
S. laoticum SMF MK330975 Laos, Vientiane Province, Vang Vieng Wesener 2019
S. meridionalis MHNG 4B-2 OM509648 Thailand, Yala Province, Bannang Sata District, Bang Lang National Park, near Than To Waterfall Bhansali and Wesener 2022
S. nigrum SMF MK330976 Laos, Champasak Province, Muang Bachieng, Ban Lak 35, Tad Etu Wesener 2019
S. peterjaegeri SMF SD553 MK330972 Laos, Luang Prabang Province, SE Luang Prabang, Nam Khan, Ban Pak Bak, Houay Kho Wesener 2019
S. phouloei ZMUC00040257 MK330974 Laos, Houaphan Province, Phou Loei Wesener 2019
S. schwendingeri MHNG LT 10/03 MK330978 Laos, Vientiane Province, trail to Tham Pou Kham, W. of Vang Vieng Wesener 2019
Sphaerobelum sp. L07 ZMUC00040261 MK330979 Laos, Khammouane Province, Ban Khounkham [Khun Kham] (Nahin) Wesener 2019
Sphaerobelum sp. L10 SMF MK330980 Laos, Vientiane Province, Vang Vieng, W. of Nam Song, Tham Nam Or Khem Wesener 2019
S. spinatum ZMUC00040258 MK330973 Laos, Vientiane Province, Phou Khao Khouay Wesener 2019
S. truncatum FMNH-INS 0000 072 674 JN885184 Thailand, Nan Province, Song Khwae District, Na Rai Luang Subdistrict, Pang Hi Village Wongthamwanich et al. 2012
S. tujiaphilum SCAU SD02 OP339783 China, Guizhou, Tongren City, Jiangkou County, Guanhe Town, Sidu Village Zhao et al. 2022
S. turcosa sp. nov. SPPL1 CUMZ-Zeph0012 OR530087 Thailand, Loei Province, Mueang Loei District, Phu Pha Lom Forest Park This study
S. turcosa sp. nov. SPPL2 CUMZ-Zeph0012 OR530088 Thailand, Loei Province, Mueang Loei District, Phu Pha Lom Forest Park This study
Genus Zephronia Gray, 1832
Z. dawydoffi ZFMK Myr4504 MK330971 N/A Wesener 2019
Z. lannaensis ZFMK MYR4911 OM509631 Thailand, Chiang Mai Province, Mae Rim District, Mae Sa Valley Bhansali and Wesener 2022
Z. laotica ZFMK Myr3502 MK330977 Laos, Champasak Province, east of Mekong, Garden of Erawan Riverside Hotel Wesener 2019
Z. ovalis ZFMK Myr 0832 JX486068 Vietnam, Dong Nai Province, Cat Tien National Park Golovatch et al. 2012
Z. panhai ZFMK MYR8116 OM509645 Thailand, Ratchaburi Province, Ratchaburi and Photharam District, 18–20 km WNW of Ratchaburi Bhansali and Wesener 2022
Z. phrain MYR3500 OM509635 Thailand, Chiang Mai Province, Chiang Mai District, Doi Suthep, behind tourist market Bhansali and Wesener 2022
Zephronia siamensis CUMZ OR530089 Thailand, Chonburi Province, Sichang District, Koh Sichang This study
Zephronia sp. NHMDK K45 MW898741 Thailand, Prachuap Khiri Khan Province, Mueang district, Aow Noi Temple Rosenmejer et al. 2021
Zephronia sp. 1 ZFMK MYR8787 MW898740 Thailand, Nakhon Si Thammarat Province, Sichon District, Khao Lark Waterfall Rosenmejer et al. 2021
Zephronia sp. 2 NHMD K56x9 OM509650 Thailand, Kanchanaburi Province, Si Sawat District, 50 km W of Kanchanaburi, Erawan Waterfall Bhansali and Wesener 2022
Order Glomerida
Family Glomeridae Leach, 1815
Genus Glomeris Latreille, 1802
G. marginata ZFMK18996 MG931021 Luxemburg, Schengen Reip and Wesener 2018
Genus Hyleoglomeris Verhoeff, 1910
H. japonica MS20210617-02 LC713423 Japan, Kanagawa Prefecture, Fujisawa-shi, Enoshima Island Kuroda et al. 2022

The COI data included 31 specimens, representing 19 specimens of the genus Sphaerobelum and 10 specimens of the genus Zephronia (Table 1). Two species of the order Glomerida, viz. Glomeris marginata (Villers, 1789) and Hyleoglomeris japonica Verhoeff, 1910 were used as the outgroups.

CodonCode Aligner (ver. 4.0.4, CodonCode Corporation) was used to assemble the forward and reverse sequences and to check for errors and ambiguities. All sequences were checked with the Basic Local Alignment Search Tool (BLAST) provided by NCBI and compared with reference sequences in GenBank. Sequence alignment (660 bp) was done with MUSCLE (ver. 3.6, see muscle; Edgar 2004). MEGA11 (ver. 11.0.10, see; Tamura et al. 2021) was used to (1) check for stop codons, (2) translate sequences into amino acids, and (3) calculate uncorrected pairwise p-distances among sequences. Pairwise deletion of missing data was applied and all positions containing ‘N’s were omitted for each sequenced pair in the analysis.

The best-fit substitution model was implemented using JModelTest2 on XSDXE 2.1.6 (Darriba et al. 2012) through CIPRES Gateway. A phylogenetic tree was constructed using maximum likelihood (ML). The shape parameter of the gamma distribution, based on 16 rate categories, was estimated using maximum likelihood analysis. ML trees were inferred with RAxML (ver. 8.2.12, see; Stamatakis 2014) through the CIPRES Science Gateway (Miller et al. 2010) using a GTR+G substitution model and 1000 bootstrap replicates to assess branch support.


COI sequence data

Uncorrected p-distances between the sequences range from 0.00 to 0.32 (Table 2). The mean interspecific sequence divergence within Sphaerobelum was 0.19 (range: 0.10–0.24). The mean sequence divergence between S. turcosa sp. nov. and other Sphaerobelum species was 0.20 (range: 0.17–0.23). The mean interspecific sequence divergence within Zephronia was 0.19 (range: 0.12–0.23). The mean sequence divergence between S. turcosa sp. nov. and Zephronia was 0.20 (range: 0.18–0.21). The mean sequence divergence between Sphaerobelum and Zephronia was 0.21 (range: 0.17–0.25).

Table 2.

Estimates of cytochrome c oxidase I (COI) sequence divergences (uncorrected p-distances) within and among Zephroniidae species and related taxa (rounded to two decimal places).

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
1 Sphaerobelum benquii
2 Sphaerobelum bolavensis 0.21
3 Sphaerobelum denticulatum 0.20 0.20
4 Sphaerobelum huzhengkuni 0.18 0.22 0.18
5 Sphaerobelum lachneeis 0.23 0.20 0.21 0.21
6 Sphaerobelum laoticum 0.19 0.21 0.18 0.16 0.21
7 Sphaerobelum nigrum 0.19 0.19 0.20 0.19 0.21 0.19
8 Sphaerobelum peterjaegeri 0.19 0.16 0.19 0.18 0.21 0.19 0.19
9 Sphaerobelum phouloei 0.20 0.18 0.17 0.17 0.21 0.18 0.19 0.18
10 Sphaerobelum schwendingeri 0.19 0.18 0.18 0.17 0.21 0.14 0.20 0.18 0.17
11 Sphaerobelum sp. L07 0.21 0.21 0.22 0.20 0.24 0.21 0.21 0.19 0.20 0.20
12 Sphaerobelum sp. L10 0.19 0.19 0.20 0.21 0.22 0.16 0.17 0.18 0.18 0.16 0.19
13 Sphaerobelum aesculus 0.20 0.20 0.21 0.19 0.24 0.21 0.22 0.19 0.21 0.20 0.22 0.20
14 Sphaerobelum meridionalis 0.19 0.20 0.20 0.18 0.22 0.18 0.20 0.18 0.17 0.18 0.21 0.19 0.17
15 Sphaerobelum spinatum 0.22 0.18 0.20 0.20 0.22 0.20 0.21 0.19 0.18 0.20 0.20 0.20 0.24 0.22
16 Sphaerobelum truncatum 0.21 0.18 0.20 0.19 0.21 0.18 0.20 0.10 0.18 0.19 0.21 0.19 0.20 0.19 0.21
17 Sphaerobelum tujiaphilum 0.20 0.21 0.18 0.12 0.21 0.18 0.20 0.19 0.17 0.17 0.21 0.21 0.21 0.17 0.19 0.20
18 Sphaerobelum turcosa sp. nov. SPPL1 0.21 0.19 0.20 0.18 0.23 0.19 0.20 0.18 0.17 0.18 0.21 0.20 0.21 0.20 0.21 0.18 0.18
19 Sphaerobelum turcosa sp. nov. SPPL2 0.20 0.19 0.20 0.18 0.23 0.18 0.20 0.18 0.17 0.18 0.21 0.19 0.21 0.20 0.21 0.18 0.18 0.00
20 Zephronia dawydoffi 0.21 0.22 0.22 0.18 0.23 0.20 0.19 0.20 0.19 0.21 0.20 0.21 0.20 0.19 0.21 0.20 0.20 0.18 0.18
21 Zephronia lannaensis 0.22 0.19 0.22 0.20 0.22 0.22 0.20 0.21 0.21 0.21 0.22 0.22 0.22 0.20 0.22 0.20 0.20 0.20 0.20 0.17
22 Zephronia laotica 0.25 0.23 0.22 0.20 0.24 0.22 0.19 0.21 0.21 0.23 0.23 0.24 0.21 0.20 0.23 0.22 0.21 0.20 0.20 0.16 0.18
23 Zephronia ovalis 0.22 0.21 0.24 0.21 0.23 0.23 0.20 0.20 0.22 0.23 0.25 0.22 0.23 0.23 0.22 0.21 0.22 0.20 0.20 0.15 0.20 0.16
24 Zephronia panhai 0.20 0.20 0.23 0.21 0.23 0.21 0.20 0.21 0.22 0.21 0.23 0.22 0.22 0.21 0.21 0.21 0.19 0.19 0.19 0.18 0.15 0.20 0.19
25 Zephronia phrain 0.22 0.21 0.24 0.19 0.24 0.20 0.17 0.20 0.20 0.20 0.22 0.21 0.21 0.21 0.22 0.21 0.20 0.19 0.19 0.19 0.22 0.19 0.20 0.21
26 Zephronia siamensis 0.21 0.21 0.21 0.19 0.24 0.22 0.19 0.19 0.19 0.23 0.21 0.21 0.19 0.19 0.21 0.20 0.20 0.19 0.19 0.10 0.19 0.14 0.15 0.19 0.19
27 Zephronia sp. 0.23 0.21 0.23 0.21 0.24 0.19 0.21 0.19 0.20 0.20 0.20 0.19 0.20 0.20 0.21 0.21 0.19 0.20 0.20 0.20 0.23 0.22 0.23 0.21 0.20 0.21
28 Zephronia sp. 1 0.23 0.20 0.24 0.21 0.24 0.23 0.20 0.20 0.21 0.22 0.22 0.22 0.20 0.21 0.22 0.21 0.21 0.21 0.21 0.22 0.22 0.21 0.22 0.20 0.21 0.21 0.17
29 Zephronia sp. 2 0.19 0.20 0.20 0.19 0.20 0.19 0.19 0.18 0.21 0.21 0.22 0.20 0.19 0.18 0.21 0.18 0.18 0.19 0.19 0.17 0.13 0.18 0.18 0.12 0.21 0.17 0.19 0.21
30 Glomeris marginata 0.29 0.29 0.29 0.27 0.33 0.28 0.29 0.28 0.27 0.30 0.29 0.29 0.28 0.30 0.28 0.29 0.28 0.29 0.29 0.30 0.30 0.31 0.30 0.30 0.29 0.29 0.27 0.29 0.29
31 Hyleoglomeris japonica 0.29 0.29 0.30 0.29 0.33 0.28 0.30 0.30 0.27 0.28 0.30 0.28 0.29 0.32 0.30 0.30 0.29 0.30 0.30 0.30 0.31 0.31 0.32 0.30 0.30 0.31 0.28 0.31 0.31 0.15

In the phylogenetic tree based on the COI gene (Fig. 1), the clade of Zephroniidae (Sphaerobelum + Zephronia) is well supported by ML (bootstrap support = 100), but the relationships among Sphaerobelum and Zephronia species could not be resolved.

Figure 1. 

The COI gene tree based on maximum likelihood analysis of cytochrome c oxidase I (COI) (660 bp). Numbers at nodes indicate branch support based on bootstrapping. Scale bar: 0.6 substitutions per site. # marks branches with <50% bootstrap support. The colored area marks Sphaerobelum turcosa sp. nov.


Family Zephroniidae Gray, 1843

Subfamily Zephroniinae Gray, 1843

Tribe Zephroniini Gray, 1843

Genus Sphaerobelum Verhoeff, 1924

Sphaerobelum turcosa Srisonchai & Pimvichai, sp. nov.

Figs 2, 3, 4, 5

Materials examined

Holotype ♂ (CUMZ-Zeph0011), Thailand, Loei Province, Mueang Loei District, Phu Pha Lom Forest Park, 383 m a.s.l., 17°33'16"N, 101°52'06"E, 10/07/2014, leg. R. Srisonchai and C. Sutcharit.

Paratypes. 5 ♂, 2 ♀ (CUMZ-Zeph0012), same data as holotype. 1 ♂, 2 ♀ (CUMZ-Zeph0012), same data as holotype, 01/08/2020 and 25/09/2021, leg. P. Pimvichai, P. Prasankok and S. Saratan. 1 ♂, 2 ♀ (CUMZ-Zeph0012), same District, Wat Phu Pha Lom, 265 m a.s.l., 17°33'16"N, 101°52'04"E, 14/05/2008, leg. C. Sutcharit.


The specific name is a Latin adjective, meaning ‘turquoise, greenish-blue mineral,’ and refers to the general body color of living specimens.


Coxal process on leg 2 sharply projecting, tarsi of legs 4–21 with 4/5/6/7/8 ventral spines. Similar in these respects to S. lachneeis, S. schwendingeri and S. laoticum, but S. turcosa sp. nov. differs from them by the combination of several characters, viz. body yellow contrasting to dominant greenish-blue color (vs. dark green/black); mesal margin of femur with teeth (vs. without teeth); vulva board and large, covering mesal 2/3 of coxa (vs. narrower, covering mesal 1/3 or half of coxa); anterior telopod consisting of 4 conspicuous telopoditomeres (vs. 3 telopoditomeres); immovable fingers of posterior telopod slender (vs. strongly humped and swollen).

Description of the new species

Measurements : Male Holotype. Body length ca 18.5 mm. Width, of thoracic shield = 9.5 mm, of tergite 8 = 10.3 mm (= broadest). Height, of thoracic shield = 5.1 mm, of tergite 7 = 5.3 mm (= highest). Male: body length = 15.2–18.4 mm. Width, of thoracic shield = 7.9–9.0 mm, of tergite 8 = 8.7–9.4 mm. Height, of thoracic shield = 4.8–5.6 mm, of tergite 7, 5.2–6.2 mm. Female: body length = 20.6–24.5 mm. Width, of thoracic shield = 6.3–10.6 mm, of tergite 8 = 7.2–11.6 mm. Height, of thoracic shield = 5.4–6.0 mm, of tergite 7, 5.7–6.7 mm.

Coloration : Live animals yellow with contrasting greenish-blue anterior margins of tergites and darker blue dorsal axial stripe (Fig. 2A–D), thoracic shield with a large, paramedian, greenish-blue band at middle (Fig. 2A–C), anal shield with a large, greenish-blue diamond at axial line (Fig. 2B, C), head, collum and groove of thoracic blackish to dark blue (Fig. 2A), legs, antennae, paratergite depressions and venter light brown to brown, venter brown to yellow brownish; coloration in alcohol, after more than 10 years of preservation, faded to light yellow with contrasting greenish-blue anterior margins of tergites, head, collum and groove of thoracic dark blue to blue, legs, antennae, paratergite depressions and venter brown to yellowish.

Figure 2. 

Habitus, live coloration. Sphaerobelum turcosa sp. nov., ♀ paratype A, E sublateral views B–D enrolled, sublateral, lateral, dorsal views, respectively. Scale bars: 5 mm.

Head : trapezoid, anterior part of the head with many long setae, posterior part densely dimpled; anterior margin of labrum with a single tooth. Eyes with 37–63 ocelli (male) or 55–67 (female). Aberrant ocellus located inside antennal groove.

Antennae : short, with rounded joints, extending posteriorly to leg-pair 3. Lengths of antennomeres: 2<3=4<1<5<6. All antennomeres densely pubescent, sensilla basiconica surrounding apical disc. Last antennomere thickened, apically widened and well rounded (Fig. 2A). Apical disc with 22–42 apical cones (male) or 21–29 (female). No sclerotized crest/ridge between antenna socket and eye field. Tömösváry organ located between eye field and antenna socket, next to, but separated from eye field.

Gnathochilarium : Structure typical of the Sphaerotheriida. Palpi with sensory cones arranged in clusters.

Mandibles : not dissected.

Collum : with glabrous surface, except for anterior and posterior margin with a few isolated and long setae.

Stigmatic plates : first stigmatic plate rounded, apex well-rounded, slightly curved towards coxa (Fig. 3A).

Figure 3. 

Sphaerobelum turcosa sp. nov. A–C ♂ holotype D, E ♀ paratype A first left coxa with stigmatic plate B coxa of second leg with gonopore C ninth right leg D coxa and prefemur of second leg with vulva E subanal plate. Scale bars: 0.5 mm.

Laterotergites : laterotergite 1 strongly projecting into a sharp tip. Laterotergite 2 with a broad, stout projection and a deep notch at lateral margin, like following laterotergites.

Following tergites : surface glabrous, shining, except the groove of paratergite with tiny setae. Tips of paratergites of midbody tergites projecting posteriorly.

Thoracic shield : surface glabrous as in tergites. Shallow grooves with few setae, surface glabrous, no keels.

Endotergum : Posterior margin (pm) flat, regular (Fig. 5A). Outer area (oa) without setae. Middle area (ma) with a single row, conspicuous, elliptical cuticular impressions (cp); distance between impressions as long as individual diameter (Fig. 5B). Bristles arranged in two rows, tip of the longest bristles not extended beyond posterior margin or not reaching to posterior margin (Fig. 5A). Inner area (ia) without tubercles or setae, but with small pits (Fig. 5D).

Anal shield : slightly sexually dimorphic, in female large and well-rounded (Fig. 2B), in male slightly more rectangular, in both sexes glabrous. Surface similar to that of tergites. Underside with a single, very short, black locking carina, six times shorter than width of last laterotergite.

Legs : leg-pair 1 with 1 or 2 ventral spines, leg-pair 2 with 3 or 4, leg-pair 3 with 5 or 6. First two leg-pairs without an apical spine. Leg pairs 4–21 with 6 or 7 ventral spines and one apical spine. In leg 9, femur 1.6 times, tarsus 3.5 times longer than wide (Fig. 3C). Femur extended mesally into a dentate margin featuring 10–14 teeth. All podomeres densely setose. Coxa with a large and marginally toothed process. Coxal process absent at first leg and sharply projecting at second (Fig. 3B). Prefemur at apical margin with a projection laterally and mesally. Lateral projection triangular and sharply edged, juxtaposed to coxal process (Fig. 3C).

Female sexual characters : vulva large, covering 2/3 of coxa, located at mesal margin, extending mesally to anterior third of prefemur (Fig. 3E). Operculum rounded, mesal margin projecting into a well-rounded lobe 1/2 as high as remaining operculum. Subanal plate: large and wide, divided by a suture into two halves. Densely setose (Fig. 3D).

Male sexual characters : gonopore large, covered with a single, undivided, triangular, sclerotized plate (Fig. 3B).

Anterior telopods (Fig. 4A–C): First podomere rectangular, slightly wider than long. Telopoditomere 2 large, as long as telopoditomere 3. Immovable finger (process of telopoditomere 2) wide, located posteriorly, but partly visible laterally in anterior view, projecting to half of movable finger (telopoditomeres 3 and 4), slightly curved, apically with a rounded tip. Telopoditomeres 3 and 4 divided by a short and weak suture, this suture being almost visible in lateral view (Fig. 4A–C). Telopoditomere 3 large, cylindrical, slender, 1.2 times longer than wide, 2 times longer than telopoditomere 4 (Fig. 4A, C). Telopoditomere 4 short, well-rounded, posterior face with two small, sclerotized spot and triangular spines (Fig. 4B). All podomeres covered with long setae.

Figure 4. 

Sphaerobelum turcosa sp. nov. A–C ♂ holotype D–F ♂ paratype A–C left anterior telopods, anterior, posterior and lateral views, respectively D, E left posterior telopod, posterior, subventral views F posterior telopods, anterior view. Scale bars: 0.5 mm.

Figure 5. 

Sphaerobelum turcosa sp. nov. ♂ paratype, SEM micrographs of the endoterga on the midbody segment. A all areas of endotergum, posterior margin (pm), outer area (oa), middle area (ma), cuticular impressions (cp) and inner area (ia) B middle area and cuticular impressions C bristles D inner area.

Posterior telopods (Fig. 4D–F): inner horns with sharp-edged tips, slightly curved caudad. Telopodite consisting of four podomeres. First telopoditomere rectangular, slightly longer than wide. Immovable finger (process of telopoditomere 2) as long as movable finger, consisting of telopoditomeres 3 and 4. Immovable finger wide, 2.5 times longer than wide, with a characteristic, distally swollen, clearly rounded apically, apex only slightly wider than base; tip strongly curved when seen in dorsolateral view. Immovable finger in anterior view with a small spine, at middle with sclerotized spot. Telopoditomere 3 long and slender, 2.5 times longer than wide, with a membranous lobe at a excavate inner margin. Telopoditomere 4 very short and slender, only 4.5 times shorter than telopoditomere 3, 1.5 times longer than wide, slightly tapering apically. Telopoditomere 4 with one small, weak spine at margin towards immovable finger. Telopoditomere 1 and 2 at both sides covered by setae. Telopoditomere 3 only basally in anterior view with setae, remaining part, as well as telopoditomere 4 glabrous.

Distribution and habitat

Currently known only from the type locality. All specimens were crawling openly on the bottom of several holes in humid rocks (Fig. 6). The stark bright color invited collectors to pick them up.

Figure 6. 

Distribution and type locality of Sphaerobelum turcosa sp. nov. A distribution map of Sphaerobelum species in Thailand B, C limestone habitat at the type locality.

Key to species of the genus Sphaerobelum in Thailand (4 species)

1 Legs 4–21 usually with one apical spine. Posterior telopods: immovable finger of telopoditomere 2 without membranous spot 2
Legs 4–21 usually with three apical spines. Posterior telopods: immovable finger of telopoditomere 2 with membranous spot, visible in posterior view 3
2 Greenish-blue body color. Male body length 15.2–18.4 mm. Endotergum with regular flat margin (Fig. 5). Leg 3 without apical spine. Coxa of second leg laterally with a sharp and long process (Fig. 3B, D). Posterior telopods: distal part of immovable finger of telopoditomere 2 moderately enlarged, tip strongly curved S. turcosa sp. nov.
Brown body color. Male body length 18.6–24.0 mm. Endotergum with ‘rectangle-wavy’ margin. Leg 3 with one apical spine. Coxa of second leg laterally without a sharp and long process. Posterior telopods: distal part of immovable finger of telopoditomere 2 strongly enlarged, tip not curved S. truncatum Wongthamwanich, 2012
3 Endotergum with two rows of bristles. First coxae with mesal process. Prefemur of midbody legs with mesal process. Telopoditomere 3 and 4 of anterior telopods clearly separated S. meridionalis Bhansali & Wesener, 2022
Endotergum with one row of bristles. First coxae without mesal process. Prefemur of midbody legs without mesal process. Telopoditomere 3 and 4 of anterior telopods incompletely fused S. aesculus Rosenmejer & Wesener, 2021


The new species can be distinguished from congeners by its greenish-blue color in combination with (1) a protruding coxal process, (2) a slender shape of the immovable finger, and (3) the shape of the posterior telopod. Yet, on the basis of morphology, little can be said about the relationships with other putatively closely related species. The overlapping COI p-distances and the phylogenetic tree were unable to resolve the relationships both within and among the genera Sphaerobelum and Zephronia. A similar unresolved tree was reported for the genus Sphaerobelum by Wesener (2019). Thus, the phylogenetic relationships of the Sphaerobelum and Zephronia species remain unclear and need further investigations.

The new species exhibits a striking greenish-blue coloration, by which it joins other brightly colored millipedes such as the genus Apheloria (A. polychroma) and the genus Desmoxytes (D. purpurosea, D. rubra and D. aurata). Species of this latter genus are not only very colorful, but they also have long spine-like paraterga. These characteristics are probably aposematic (Enghoff et al. 2007; Srisonchai et al. 2018).

The occurrence of the new species in Phu Pha Lom Forest Park is possibly correlated with the type of habitat/microhabitats. Due to its heterogenous topologies, its strongly irregular geomorphology and the good drainage of the limestone substrate, the type locality of S. turcosa sp. nov. probably provides suitable conditions to harbour a rich soil fauna.

With the discovery of S. turcosa sp. nov., the number of Sphaerobelum species in Thailand increases to four, which is still less than the number of Sphaerobelum species in Laos (10 species) and Vietnam (6 species) (Wesener 2019; Semenyuk et al. 2020), but more than in Cambodia and Myanmar, where hitherto no Sphaerobelum species have been reported (Likhitrakarn et al. 2014, 2015).


We thank our colleagues of the Animal Systematic Research Unit (ASRU), Chulalongkorn University, Mr. Sathit Saratan (Sirindhorn Museum) and the Department of National Parks, Wildlife and Plant Conservation of Thailand for assistance in collecting specimens. We are grateful to the editor and referees for their critical comments which helped to improve the manuscript.

Additional information

Conflict of interest

The authors have declared that no competing interests exist.

Ethical statement

The approval of the Animal Care and Use Committee (Protocol Reviews No. IACUC-KKU-136/64 from Khon Kaen University) and No. 1723018 from Chulalongkorn University.


This research was funded by the Fundamental Fund (Basic Research) of Khon Kaen University and the Research Grant for New Scholar (RGNS65-056).

Author contributions

Conceptualization: PP. Funding acquisition: RS. Investigation: RS, PP, NL. Resources: PP, CS. Supervision: PP. Writing – original draft: RS. Writing – review and editing: PP, TB, CS.

Author ORCIDs

Ruttapon Srisonchai

Natdanai Likhitrakarn

Chirasak Sutcharit

Thierry Backeljau

Piyatida Pimvichai

Data availability

All of the data that support the findings of this study are available in the main text.


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