Holotype : ANU ZR24046, adult male from Mountain Jinuo, Jinghong City, Xishuangbanna Dai Autonomous Prefecture, Yunnan Province, China (22.009245°N, 101.014120°E; elevation 1,050 m asl), collected on 5 June 2024, by TRZ. Paratype: ANU ZR25021, one juvenile male from the same location as the holotype, collected on 7 August 2023, by TRZ.

Calamaria synergis sp. nov. can be distinguished from all other congeners by the following combination of morphological characters: eight enlarged maxillary teeth; rostral higher than wide; prefrontal shorter than frontal and contacting the first two supralabials; mental not in contact with anterior chin shields; single preocular and postocular; four supralabials, with the 2^nd and 3^rd contacting the eye; five infralabials; five scales surrounding the paraparietal; ventrals 161–166; subcaudals 20–23, paired; dorsal scales reduced to six rows at the tail base and further to four rows near the terminal subcaudals; tail relatively short (6.6–9.2% of total length), abruptly tapering at the tip; dorsum blackish-brown with a distinct pale nuchal ring; two outermost dorsal scale rows pale khaki with upper margins darkened; ventral surface uniform pale khaki.

(Fig. 2). Specimen ANU ZR24046 is in excellent condition. Body slender and cylindrical (SVL 258 mm, TL 284 mm); body thickness ~4.3–5.9 mm; tail not as thick as body, base of tail 3.6 mm thick. Tail short (TaL 26 mm, TaL/TL 9.2%); tail uniformly cylindrical in the anterior part, then abruptly tapering at tip; tip of tail obtusely pointed; head small, elliptical in dorsal view (HL 7.3 mm, HW 4.6 mm, HH 3.7 mm); eye small and round (EyeD 1.2 mm), larger than eye-mouth distance (Eye-MouthD 0.9 mm), ED/HL 16.4%.

Figure 2. 

Calamaria synergis sp. nov. in preservative, holotype (ANU ZR24046, adult male). A. Dorsal view of body; B. Ventral view of body; C. Dorsal view of head; D. Ventral view of head; E. Right lateral view of head; F. Left lateral view of head. Photographs by TRZ.

Rostral higher than wide (width 1.4 mm, height 1.6 mm), portion visible from dorsal aspect almost equal to the length of the prefrontal suture; prefrontal (length 1.8 mm) shorter than frontal (length 3.1 mm), not entering orbit, in contact with 1^st and 2^nd supralabial; frontal hexagonal, longer (length 3.1 mm) than wide (width 2.4 mm), ~3.0 times maximum width (0.8 mm) of supraocular; paraparietal surrounded by five scales; preocular 1/1 (left/right, hereinafter), higher than wide, slightly higher than postocular, not as high as eye diameter; postocular 1/1, higher than wide; nasals small, barely surrounding nostrils, surrounded by the 1^st supralabial, rostral and prefrontal; supralabials 4/4, 2^nd and 3^rd entering orbit, 4^th largest, relative supralabial width 4>2>1>3; mental triangular, not in contact with the anterior chin shields; infralabials 5/5, the first three pairs touching anterior chin shields, the first pair meeting in the midline, 4^th largest; anterior chin shields longer than wide (length 2.1 mm, width 1.1 mm), pentagonal, meeting in the midline; posterior chin shields shorter than the anterior ones (length 1.6 mm), touching anteriorly and separated posteriorly by the first gular scales.

Dorsal scales in 13 rows throughout the body, reducing to six rows above the 7^th subcaudal and to four rows above the penultimate pair of subcaudals. Dorsal scales homogeneous in size and entirely smooth; vertebral row not enlarged. Ventrals 161. Anal plate undivided. Subcaudals 20, paired, smooth; terminal scale single and rigid.

Maxillary teeth modified (enlarged), eight on each side (8/8).

(Fig. 3A). Dorsum of head and upper parts of supralabials brownish black, scattered with indistinct white flecks; ventral surface of head pale khaki, with black speckles on the infralabials and anterior portion of the anterior chin shields. The dorsal surface of the body and the tail brownish black with iridescent white flecks distributed over most dorsal scales. Two outermost dorsal scale rows are slightly pale khaki, with upper margins partially darkened, forming two indistinct, narrow black stripes along each side of the body. A distinct pale khaki nuchal ring is present, extending dorsally from the level of the 2^nd–4^th ventral scales, equivalent in width to two dorsal scale rows. No pale rings or blotches are present on the neck or tail. Ventral scales of the body and subcaudal scales of the tail are pale khaki, with black pigmentation on the outermost corners; small black flecks are present along the median line of the ventral tail surface, extending from the 2^nd subcaudal scale to the tail tip.

Figure 3. 

In situ photographs of Calamaria synergis sp. nov. and its congeners in life. A. Calamaria synergis sp. nov. (ANU ZR24046); B. C. andersoni (ANU ZR25022); C. C. yunnanensis (QHU R2024054). Photographs by TRZ (A, B) and T.Y. Zhang (C).

(Fig. 2). After nearly one year in 75% ethanol, the dorsum of the body and tail remains brownish black; white flecks on the dorsal scales and narrow black stripes along the flanks are still visible. The nuchal ring and ventral surfaces of the body have faded to greyish white.

Specimen ANU ZR25021 (paratype), a juvenile male (see Fig. 4), has a smaller body size (SVL 127 mm, TaL 9 mm, HL 6.0 mm, HW 3.1 mm, EyeD 0.8 mm, Eye-MouthD 0.5 mm). Compared to the holotype, it exhibits a higher number of ventrals (VEN 166 vs 161), subcaudals (SC 23 vs 20), and lacks black flecks along the median line of the ventral tail surface (vs present in the holotype).

Figure 4. 

Calamaria synergis sp. nov. in preservative, paratype (ANU ZR25021, juvenile male). A. Dorsal view of body; B. Ventral view of body. Photographs by TRZ.

The specific name synergis is a Latin noun given in the apposition, derived from the Greek synergos (συνεργός), meaning “working together”. It emphasises that the resolution of the taxonomic status of the new species is the outcome of coordinated international scientific cooperation. The name is given in reference to both the collaborative effort involved in describing this new species and the broader need for joint action to address the complex taxonomic problems within the genus Calamaria in the future. We suggest the following common names: “Mountain Jinuo reed snake” (English), “基诺两头蛇” (Chinese), “Rắn mai gầm hiệp lực” (Vietnamese), and “Цзинхунская карликовая змея” (Tszinhunskaya karlikovaya zmeya, Russian).

Comparative morphological data for the new species and the currently recognised members of the genus Calamaria from Indochina to southern China are presented in Table 3 and Suppl. material 1: figs S1, S2.

Calamaria synergis sp. nov. is readily distinguished from C. lumbricoidea (distributed in Thailand, Malaysia, Singapore, Indonesia, Brunei, and the Philippines) and C. schlegeli (Thailand, Malaysia, Indonesia, and Singapore) by having four supralabials, with the second and third in contact with the eye (vs 5 supralabials with the third and fourth in contact with the eye). Furthermore, both species are restricted to the areas south of the Isthmus of Kra in Peninsular Malaysia and have not been recorded from mainland Indochina.

The new species also differs from C. lovii ingermarxorum Darevsky & Orlov (Gia Lai Province, Vietnam), C. nebulosa (Phongsaly Province, Laos; possibly northern Thailand), C. thanhi (Quang Binh Province, Vietnam), and C. yunnanensis (Yunnan Province, China; possibly northwestern Vietnam) by the presence of a preocular scale (vs absent).

Calamaria synergis sp. nov. differs from C. abramovi (Kon Tum Province, Vietnam) in having the paraparietal surrounded by five shields and scales (vs six), fewer subcaudal scales in males (SC 20–23 vs 26), a maximum total length in males (max TL 284 mm vs 139 mm), shorter relative tail length in males (6.6–9.2% vs 13.3%), a non-tapering tail (vs gradually tapering), an obtusely pointed tail tip (vs sharply pointed), a blackish-brown dorsum (vs uniformly black), and pale khaki unspotted ventrals (vs yellow-orange spots).

Compared to C. andersoni (Fig. 3B; Suppl. material 1: Figs S1B, S2B), Calamaria synergis sp. nov. differs by having five shields surrounding the paraparietal (vs 6 in C. andersoni), a smaller maximum total length in males (max TL 284 mm vs 351 mm), eight maxillary teeth (vs 9), unspotted pale khaki ventrals (vs bright orange to orange-yellow), and the presence of light neck rings (vs absent).

The new species is distinct from C. arcana (Zhejiang, Guangdong, Fujian, and Hunan provinces, China) by five shields surrounding the paraparietal (vs 6), fewer ventrals in males (VEN 161–166 vs 170–176), unspotted pale khaki ventrals (vs orangish-red), and the presence of light neck rings (vs absent).

Calamaria synergis sp. nov. is further separated from C. berezowskii (Sichuan Province, China) by having more ventrals in males (VEN 161–166 vs 149–155), five shields surrounding the paraparietal (vs six), and the presence of light neck rings (vs absent).

The new species differs from C. buchi (Lam Dong Province, Vietnam) by the mentals not contacting the chin shields (vs contacting), fewer ventrals (161–166 vs 221–236), a blackish-brown dorsum (vs blackish with small pale spots), and unspotted pale khaki ventrals (vs yellow, unspotted).

From C. concolor (Thua Thien-Hue and Quang Nam provinces, Vietnam), the new species differs in having the mental not contacting the chin shields (vs contacting), fewer ventrals in males (VEN 161–166 vs 209), a smaller maximum total length in males (max TL 284 mm vs 578 mm), a non-tapering tail (vs slightly tapered), a blackish-brown dorsum (vs uniform orangish-red), unspotted pale khaki ventrals (vs bright red), and pale neck blotches (vs absent).

The new species is distinct from C. dominici (Dak Nong Province, Vietnam) in having five shields surrounding the paraparietal (vs 6), a non-tapering tail (vs slightly tapering), a blackish-brown dorsum (vs dark with irregular yellow blotches), and unspotted pale khaki ventrals (vs dark with few yellow blotches and bands).

Compared to C. gialaiensis (Gia Lai Province, Vietnam), the new species differs by the mental not contacting the chin shields (vs contacting), fewer ventrals in males (VEN 161–166 vs 191), a smaller maximum total length in males (max TL 284 mm vs 457 mm), an obtusely pointed tail tip (vs rounded), a blackish-brown dorsum (vs pale greyish-brown with a faint dark neck collar and posterior blotches), and unspotted pale khaki ventrals (vs yellowish beige).

Calamaria synergis sp. nov. can be distinguished from C. jinggangensis (Jiangxi and Guizhou, possibly Hunan provinces, China) by five shields surrounding the paraparietal (vs 6), slightly more ventrals in males (VEN 161–166 vs 157–158), shorter relative tail length in males (ratio TaL/TL 6.6–9.2% vs 15%), and unspotted pale khaki ventrals (vs dark orange).

The new species differs from C. pavimentata (Suppl. material 1: figs S1C, S2C), which is distributed from India and Myanmar through Indochina to Peninsular Malaysia and China (including Taiwan) and southernmost Japan, by having a higher number of ventrals in males (VEN 161–166 vs 151 in the holotype of C. pavimentata), fewer subcaudals in males (SC 20–23 vs 27 in the holotype), a non-tapering tail (vs tapered), and an obtusely pointed tail tip (vs sharply pointed).

Calamaria synergis sp. nov. is distinct from C. sangi (Kon Tum Province, Vietnam) by the mental not contacting the chin shields (vs contacting), fewer ventrals in males (VEN 161–166 vs 190), a smaller maximum total length in males (max TL 284 mm vs 373 mm), a non-tapering tail (vs slightly tapered), and the presence of neck blotches (vs absent).

The new species differs from C. septentrionalis (southern China and northern Vietnam) by the mental not contacting the chin shields (vs contacting), five shields surrounding the paraparietal (vs six), slightly more subcaudals in males (20–23 vs 15–19), a smaller maximum total length in males (max TL 284 mm vs 344 mm), an obtusely pointed tail tip (vs broadly rounded), a blackish-brown dorsum (vs dark brown or black, usually with a narrow yellow ring behind the head), and unspotted pale khaki ventrals (vs yellow with small black spots).

Calamaria synergis sp. nov. differs from C. strigiventris (Lam Dong and Khanh Hoa provinces, Vietnam) by the mental not contacting the chin shields (vs contacting), five shields surrounding the paraparietal (vs 6), slightly fewer subcaudals in males (SC 20–23 vs 29–31), a smaller maximum total length in males (max TL 284 mm vs 362 mm), a shorter relative tail length in males (ratio TaL/TL 6.6–9.2% vs 11.2–17.9%), a non-tapering tail (vs tapering), an obtusely pointed tail tip (vs abruptly pointed), a blackish-brown dorsum (vs uniform grey-brown), and unspotted pale khaki ventrals (vs bright yellow with longitudinal black stripes).

Finally, the new species differs from C. yunnanensis (see Fig. 3C, Suppl. material 1: figs S1D, S2D) by the presence of a preocular scale (vs absent), fewer ventral scales in males (VEN 161–166 vs 167–184), eight maxillary teeth (vs 9), unspotted pale khaki ventrals (vs bright orange to orange-yellow), and the presence of pale neck rings (vs absent).

Calamaria synergis sp. nov. is currently known only from tropical evergreen forest at its type locality (see Fig. 5), at an elevation of ca 1,050 m asl. This region is characterised by high herpetofaunal diversity, with several snake species occurring sympatrically in the same habitat, including Oligodon fasciolatus (Günther), Lycodon fasciatus (Anderson), Plagiopholis nuchalis Boulenger, and Trimeresurus lanna Idiiatullina, Nguyen, Pawangkhanant, Suwannapoom, Chanhome, Mirza, David, Vogel & Poyarkov (see also Idiiatullina et al. 2024; Vogel et al. 2024). It seems highly likely that the new species also occurs in the adjacent mountainous areas of eastern Myanmar, northern Laos, and northeastern Vietnam. Due to the limited information available on the ecology and potential threats of Calamaria synergis sp. nov., we recommend that the new species be classified as Data Deficient (DD) according to the IUCN Red List Categories and Criteria (IUCN 2025).

Figure 5. 

Distribution ranges of Calamaria synergis sp. nov., C. andersoni, and C. yunnanensis. Numbers indicate localities where the species have been recorded (see Suppl. material 1: table S3 for locality details).