The genus Rhopalomeris could be recognized through numerous apical sensory cones on the antennal tip, and antennomere 6 being particularly enlarged and rather strongly curved. In addition, the posterior telopods are rather strongly enlarged and stout, supplied with both prefemoral and femoral trichosteles. The femur has a distinctive and particular distocaudal process. The body is relatively large, with adults ranging from 11 to 20 mm in length. The body coloration is variable, but often useful for species identification.

Glomeris carnifex Pocock, 1889, fixed under Art. 70.3 (ICZN 1999) in Golovatch et al. (2011), misidentified as Rhopalomeris bicolor (Wood, 1865) in the original designation by Verhoeff (1906).

Rhopalomeris monacha Silvestri, 1917; R. tonkinensis Silvestri, 1917; R. variegata Golovatch & Semenyuk, 2016; R. sauda Nguyen, Sierwald & Marek, 2019; and R. nagao Nguyen, Nguyen & Eguchi, 2021.

The genus Rhopalomeris was originally typified by Verhoeff (1906) through the designation of Glomeris bicolor Wood, 1865 as the type species. However, this designation was based on specimens from Salanga Island (presently known as Phuket Island, Thailand) housed in the Berlin Museum (currently Museum für Naturkunde Berlin; ZMB), and these specimens had been previously identified by F. Karsch as G. bicolor. Although the type locality of G. bicolor is in Hong Kong (Wood 1865), Verhoeff (1906) followed Karsch’s identification, and refrained to introduce a new name to those specimens.

Furthermore, Verhoeff (1906) compared the specimens from Phuket Island with G. carnifex, noting that several characteristics were similar to his specimens. He admitted that both might be two distinct species because of possible distinctions in telopods and the number of apical sensory cones on the antennae. Verhoeff also suggested to reclassify G. carnifex under the genus Rhopalomeris.

Subsequently, Silvestri (1917) examined relevant material probably housed in the Zoological Survey of India, (formerly the Indian Museum). He synonymized G. bicolor sensu Verhoeff (1906) with R. carnifex var. pallida (Pocock, 1889) from Elphinstone Island, Mergui Archipelago, Myanmar, and redesignated R. carnifex from Tenasserim, Myanmar, as the type species.

Finally, Golovatch et al. (2011) studied the specimens of G. bicolor sensu Verhoeff (1906), from Salanga Island housed in the ZMB, and confirmed the identification of these specimens as R. carnifex. Golovatch et al. (2011) also synonymized the variety pallida with R. carnifex given the reason that the variety pallida was simply a color morph of R. carnifex, and validated that R. carnifex is the type species of Rhopalomeris, fixed under Art. 70.3 (ICZN 1999). Therefore, the millipede genus Rhopalomeris is currently known only from Myanmar, Thailand, Malaysia, and Vietnam, with a total of six nominal species involved (Fig. 1).

Peplomeris was originally described as a subgenus of Rhopalomeris (Silvestri, 1917). However, it was later raised to a genus level by Mauriès (1971), who assigned this genus to the tribe Haploglomerini, whereas Rhopalomeris belongs to the tribe Trachysphaerini (Mauriès, 1971). Nguyen et al. (2019) provided a comprehensive comparison among these two genera, highlighting key morphological differences among five Vietnamese glomerid genera. Peplomeris is characterized by simple, elongated telopods, the presence of a prefemoral trichostele, and a reduced to missing femoral trichostele. In contrast, Rhopalomeris has antennomere 6 that is unusually large, and trichosteles present in both prefemur and femur of the telopods. The antennae of Rhopalomeris also have numerous apical sensory cones like in Peplomeris.

Myanmar, south Tenasserim (Pocock 1889); Malwoon in Tenasserim (Pocock 1890); Elphinstone Island (Pocock 1889); Moulmein (Attems 1936); Taninthay Division, Tanintharyi Region, 9°56'20˝N, 98°32'22˝E, Thatay Kyun (= Pulo Ru, Ko Son) (Decker 2010). Thailand, Phuket Province, Salanga Island (= Phuket Island) (Verhoeff 1906; Enghoff 2005); Mueang Phuket District, Ko Siray, 7°53'7˝N, 98°26'14˝E, 20–50 m a.s.l. (Decker 2010); Krabi Province, Krabi District, Nai Chong (Enghoff 2005); Ao Luk, 8°10'54˝N, 98°50'30˝E, 70 m; Ban Khlong Jilat, 8°05'18˝N, 98°52'56˝E, 60 m a.s.l.; near Saengphet Cave, 8°9'46˝N, 98°53'12˝E, 80 m; Ko Lanta District, Ko Lanta Island, 80 m a.s.l.; Phang Nga Province, Ko Yao District, Ko Yao Noi, 8°9'53˝N, 98°37'20˝E, 150 m a.s.l.; Thap Put District, Had Lek Beach, 8°37'N, 98°13'E, 10 m a.s.l.; Khao Lak-Lamru National Park, 8°37'N, 98°14'E, 30–40 m; Surat Thani Province, Ko Samui District, Samui Island, Khao Phlu, 10–500 m a.s.l.; Nam Tok Na Muang Forest Park, 30 m a.s.l.; Ko Pha Ngan District, Phangan Island, Than Sadet-Ko Phangan National Park, 9°44'7˝N, 100°1'10˝E, 320 m a.s.l. (Decker 2010). Malaysia, neighboring the Malay Peninsula (Verhoeff 1906).

Myanmar – Tanintharyi Division • 2 ♂; Myeik, Kala Island; elev. 5 m a.s.l.; 12°29'38″N, 98°30'53″E; 5 Apr. 2016; C. Sutcharit, W. Siriwut, R. Srisonchai leg.; CUMZ-GLO016-1, 16-2.

Body length of unrolled specimens, 17.5–17.9 mm (♂), width 8.9–9.1 (♂).

Color faded after 15 years of preservation in alcohol (Fig. 2A–C): body blackish, with contrasting light yellow to yellow, broad to narrow bands at posterior edges of each of terga 2–11; axial stripe yellow, short, starting from behind caudal edge, not reaching 1/5–1/6 length of each tergite (Fig. 2A); in lateral view, terga 2–11 each with a large, reddish or carmine to red orange band each side, ~ 1/4–2/3 height of each tergum (Fig. 2B). Thoracic shield with a very large, lateral, reddish to red orange band each side at lateral edges, ~ 2/3–3/4 height of tergum in lateral view (Fig. 2A–C); anal shield (= pygidium) with a reddish to red-orange band at the lateral and posterior edges, ~ 2/3–3/4 height of tergum (Fig. 2B). Head, collum and antennae black to dark brown, only labrum and Tömösváry’s organ brownish (Fig. 2C), venter and legs brownish to pale yellowish (Fig. 2C).

Labrum sparsely setose (Fig. 2C). Gnathochilarium with 2+2 palps subequal in length. Eyes blackish, with 8–11+1 ommatidia, cornea convex and translucent. Antennomere 6 long, ~ 2.3–2.5× as long as its height, dorsal margin strongly curved (Figs 2C, 3A). Disk of antennomere 7 beset with 55–62 small sensory cones apically (♂) (Figs 2C, 3A). Organ of Tömösváry typical, horseshoe-shaped, suboval, elongate, ~ 1.5–1.6× as long as broad.

Figure 3. 

Rhopalomeris carnifex (Pocock, 1889), ♂ specimen from Kala Island A antenna, anterior view B leg 17, anterior view C leg 18 anterior view D, E telopod, anterior and posterior views F tip of syncoxital lobes (without scaling). Scale bars: 0.5 mm. Abbreviations: cx coxa, cxl coxal lobe, fe femur, fp femoral process, ft femoral trichostele, pf prefemur, pft prefemoral trichostele of telopod, sh syncoxital horn of telopod, sl syncoxital lobe of telopod, sn syncoxite notch, sx syncoxite, ta tarsus, ti tibia, tp tibial process.

Collum as usual, with two transverse striae. Thoracic shield with a small hyposchism field not projecting past rear tergal margin (Fig. 2B); 7–9 mostly superficial striae, only lower two or three lying in front of schism, one or two level to schism, remaining 2–4 behind schism, 6 and 7 complete striae, crossing the dorsum. Terga 3 and 4 relatively broadly rounded laterally (Fig. 2B). Following terga in front of pygidium faintly concave medially at caudal edge and with three or four striae starting above lateral edge, sometimes first and second stria fading away towards midway. Pygidium slightly concave medially at caudal edge.

♂ legs 17 (Fig. 3B) simple, rather strongly reduced, with a rather low to medium-sized, often rounded, coxal lobe and a 4-segmented telopodite. Tarsus with 4–10 strong median and 1–3 strong apical spines (Fig. 3B).

♂ legs 18 (Fig. 3C) simple, slightly reduced, without any evident outgrowths; syncoxite membranous, with a small, broad, arch-shaped syncoxite notch and a 4-segmented telopodite. Tarsus with a small, but strong apical spine.

Telopods (= ♂ legs 19) (Fig. 3D–F) with a rather large and roundly pentagonal syncoxite lobe, this being flanked by two short, spiniform, acuminate and setose syncoxite horns, the latter being evidently lower than syncoxite lobe (Fig. 3F). Telopodite 4-segmented, with a spine apically. Prefemur (Fig. 3D, E) subtrapeziform, with a conspicuous, elongated, robust, tuberculiform, distomesal prefemoral trichostele with a rounded tip, extending to about half or distal boundary of femur (Fig. 3D, E). Femur (Fig. 3D, E) subtrapeziform, with a stout, relatively short femoral trichostele in anterior view, extending apically to ~ 1/2–3/4 prefemoral trichostele, in posterior view with a rounded, slightly narrowed, subtrapeziform femoral process, this being strongly curved anterolaterally and gently tapering into an acuminate and pointed tip (Fig. 3D). Tibia stout, gently tapering distad and curved apicobasad towards femoral process, with an evident, distolateral tibial process, this being strongly curved mesad (Fig. 3E). Tarsus the smallest, subcylindrical, moderately sigmoid, strongly curved, narrowly rounded apically, with a robust and small terminal seta (Fig. 3D).

The taxonomic status of R. carnifex presents a challenge. Pocock (1889) originally described both Glomeris carnifex and G. carnifex var. pallida in the same paper. However, the original description of G. carnifex lacked details, focusing solely on body coloration and a vague collection locality (south Tenasserim, Myanmar). Pocock (1890) subsequently provided more information regarding the precise sampling locations, viz. south Tenasserim and Malwoon (= Maliwan, Kawthoung, Tanintharyi, Myanmar; Likhitrakarn et al. 2017).

In contrast, the description of G. carnifex var. pallida from Elphinstone Island contained far more detail. Pocock (1889) provided information on the number of specimens (male and female individuals), body characteristics, the 18^th pair of legs and the telopod structure, all accompanied by clear illustrations. Notably, G. carnifex and G. carnifex var. pallida differ only slightly in coloration, showing a central, longitudinal, carmine line and large, lateral, carmine spots on each tergite.

Subsequently, Silvestri (1917) provided a more detailed description, accompanied by comprehensive illustrations, while still treating R. carnifex and R. carnifex var. pallida as two different taxa. He also treated G. bicolor sensu Verhoeff (1906) as a synonym with R. carnifex var. pallida (Pocock, 1889). In a recent study, Golovatch et al. (2011) formally synonymized R. carnifex var. pallida with R. carnifex.

However, our recently obtained specimens from Kala Island, Myanmar (Fig. 1, green square) closely resemble the original description of G. carnifex var. pallida from Elphinstone Island (Fig. 1, red square) both in color pattern (Fig. 2) and morphological characters, especially the structure of their legs and telopod (Fig. 3) as described by Pocock (1889). These two geographically distant populations (ca 50 km apart) (Fig. 1) share these similarities, indicating that they probably belong to the same taxon. As R. carnifex var. pallida is now synonymized under R. carnifex (Golovatch et al. 2011), we currently identify these specimens from Kala Island, Myanmar as R. carnifex.

Although there were previous reports of R. carnifex from several localities in southern Thailand, preliminary analyses of a number of R. carnifex specimens from this area reveal notable intraspecific variation in coloration, morphology, and molecular genetics, suggesting an occurrence of cryptic species (unpublished data). Therefore, a comprehensive redescription of newly retrieved male specimens from Kala Island, Myanmar in this study, comparing them with the original description of G. carnifex var. pallida from the nearby Elphinstone Island, is essential before any taxonomic revisions of other Thai specimens can be proposed. Furthermore, the morphological redescription of R. carnifex above is thus based only on these Myanmarese specimens.

This species was described from Perak State, western Malaysia (Silvestri 1917). The species remains known only from a female holotype (Silvestri 1917). Endemic to Malaysia.

This species was described from Tonkin, Montes Mauson, 2,000–3,000 ft. a.s.l., Lang Son Province, northern Vietnam (Silvestri 1917). The species is likewise known only from a female holotype (Silvestri 1917). Endemic to Vietnam.

This species was described from Vietnam, Gia Lai Province, Kon Chu Rang Nature Reserve, 14°30'54″N, 108°32'47″E, ca 1,000 m a.s.l. (Golovatch and Semenyuk 2016) and later reported from Kon Tum Province, Kon Plong District, Bak Khe River, 14°43.450'N, 108°18.882'E, ca 1,000–1,260 m a.s.l. (Golovatch 2017). Endemic to Vietnam.

This species was described from Vietnam, Bac Kan Province, Ba Be National Park, 400–500 m a.s.l.; Vinh Phuc Province, Phuc Yen Town, Ngoc Thanh Commune, Me Linh Station for Biodiversity, 21.385°N, 105.7119°E; Tam Dao district, Tam Dao National Park, 21.460945°N, 105.647021°E (Nguyen et al. 2019); Tuyen Quang province, Cham Chu Nature Reserve; Ha Giang Province, Khau Ca Nature Reserve (Nguyen et al. 2021). Endemic to Vietnam.

This species was described from Vietnam, Cao Bang Province, Pia Oac – Pia Den National Park, 22.5540°N, 105.8622°E, 850–1,600 m a.s.l. (Nguyen et al. 2021). Endemic to Vietnam.

Holotype : Myanmar – Kayin State • ♂; Linno Gu (Lateral small cave); 16°50'52.9"N, 097°36'37.7"E; 25 Nov. 2015; F. Bréhier leg.; MY15-13/01-CUMZ-GLO093. Paratypes: Myanmar – Kayin State • 7 ♂♂ 5 ♀♀; same locality as holotype; MY15-13/01-CUMZ-GLO093) • 2 ♂♂ 2 ♀♀; same locality as holotype; MNHN-MY15-13/01.

Differs from other species of Rhopalomeris by the yellowish body with contrasting brown to blackish markings on terga 4–9 (Fig. 4A–F). Additionally, characterized by the smallest body sizes (5.1–9.7 mm in length and 2.6–4.7 mm in width), coupled with the telopod syncoxital lobe being slightly lower than lateral syncoxite horns. For further details, see key below.

Figure 4. 

Rhopalomeris nigroflava sp. nov., A–C ♂ holotype in A dorsal B lateral and C ventral views D–F ♂ paratypes D, E dorsal and F ventral views. Scale bars: 0.2 mm.

Body length of unrolled holotype,7.3 mm, width 4.1 mm. Body length of unrolled paratypes, 5.6–9.3 mm (♂), 5.1–9.7 mm (♀), width 3.1–4.8 (♂), 2.6–4.7 mm (♀).

Color faded after nine years of preservation in alcohol (Fig. 4A–F): body yellowish to brown yellowish, with contrasting brown to blackish markings on terga 4–9 (Fig. 4A, B, D, E); lateral sides of terga 10, 11, and anal shield sometimes with a pair of small, faint, dark paramedian spots, these reaching neither caudal nor lateral edges (Fig. 4A, B, D, E); head, antennae and collum brown to dark brownish, only labrum, vertex and Tömösváry’s organ light brown; venter yellow brown to light yellowish; legs pale brown to brownish, with basal part of each podomere whitish (Fig. 4C, F).

Labrum sparsely setose (Figs 4C, F, 5A). Gnathochilarium with 2+2 palps subequal in length. Eyes blackish, with 6(7)+1 (♂) ommatidia (Fig. 5A), 6–(9)+1 ommatidia (♀), cornea convex and translucent. Antennomere 6 rather short, ~ 1.7–1.8× as long as its height, dorsal margin only slightly curved (Figs 4C, 5A, C). Disk of antennomere 7 beset with 22–28 small sensory cones apically (Fig. 5A, C), 16–26 small sensory cones apically (♀). Tömösváry’s organ typical, horseshoe-shaped, oblong-oval, elongate, ~ 1.6–1.7× as long as broad (Fig. 5A, C).

Figure 5. 

Rhopalomeris nigroflava sp. nov., ♂ holotype A head and anterior part of body, ventral view B thoracic shield, lateral view C left antenna, frontal view D leg 18, anterior view. Scale bars: 1 mm (A, B), 0.2 mm (C), 0.4 mm (D). Abbreviations: cxl coxal lobe, e eggs, hy hyposchism field, K caudomedial tubercle, sc schism, sn syncoxite notch, sx syncoxite.

Collum as usual, with two transverse striae (Fig. 5A). Thoracic shield with a small hyposchism field not projecting past rear tergal margin (Fig. 5B). 7–9 mostly superficial striae, only lower 4 or 5 lying above schism, one level to schism, remaining 3 or 4 below schism, 6 or 7 complete, crossing the dorsum (Fig. 5B). Terga 3–7 rather broadly rounded laterally, with two or three striae starting above lateral edge, sometimes middle stria fading away mid-dorsally (Fig. 5B). Following terga in front of pygidium concave medially at caudal edge and with one or two striae starting above lateral edge. Male pygidium faintly concave medially at caudal edge (Fig. 4A, D, E).

♂ legs 17 (Fig. 6A–C) particularly strongly reduced, with a rather small to medium-sized, often irregularly rounded coxal lobe and a 4-segmented telopodite. Tarsus with 2–4 strong apical spines.

Figure 6. 

Rhopalomeris nigroflava sp. nov., A, B ♂ paratypes C–F ♂ holotype A–C leg 17, anterior view D, E telopod, posterior and anterior views, respectively F, G tip of syncoxital lobes (without scaling). Scale bars: 0.2 mm. Abbreviations: cx coxa, cxl coxal lobe, fe femur, fp femoral process, ft femoral trichostele, pf prefemur, pft prefemoral trichostele of telopod, sh syncoxital horn of telopod, sl syncoxital lobe of telopod, ta tarsus, ti tibia, tp tibial process.

♂ legs 18 (Fig. 5D) rather strongly reduced, with a rounded ogival syncoxital notch and a 4-segmented telopodite. Femur with a small, setose, caudomedial tubercle near apex. Tarsus with a small apical spine.

Telopods (= ♂ legs 19) (Fig. 6D–G) with a small subtrapeziform, narrowly and roundly emarginated syncoxital lobe, this being flanked by two setose syncoxite horns, each of the latter higher than syncoxital lobe (Fig. 6D, E) and crowned by a subapical setoid filament (Fig. 6F, G). Telopodite 4-segmented. Prefemur (Fig. 6E) rectangular, with a conspicuous, elongated, robust, tuberculiform, distomesal prefemoral trichostele; in anterior view, with a rounded tip, extending to about half or distal boundary of femur (Fig. 6E). Femur (Fig. 6D, E) rectangular, with a prominent, stout, relatively short femoral trichostele in anterior view, extending apically to ~ 1/2–3/4 prefemoral trichostele, in posterior view with a rounded, subtriangular femoral process, this being curved anterolaterally and gently tapering into an acuminate rounded tip distally (Fig. 6D, E). Tibia stout, gently tapering distally and curved apicobasally towards femoral process, with a rather large, distolateral tibial process strongly curved mesad (Fig. 6D, E), with a strong anterior seta in anterior view (Fig. 6D) near base of tibial process. Tarsus the smallest, subcylindrical, moderately sigmoid, strongly curved, narrowly rounded apically, with a robust and small terminal seta (Fig. 6D, E).

It seems noteworthy that a female and two male (Fig. 5C) specimens were found guarding a clutch of eggs near its head, beneath the thoracic shield. This behavior deviates from the typical reproductive strategy so far known in the entire order Glomerida, where females deposit eggs in specialized clay chambers and leave them to develop independently (Thomas et al. 1970; Janssen 2013). This is the first instance of paternal brood care observed in Glomerida. Therefore, this newly discovered species presents fascinating traits worthy of a dedicated future study.

The specific epithet nigroflava is derived from the Latin niger meaning black and flavus meaning yellow, in reference to the dark bands on a yellowish dorsum, adjective in feminine gender.