Calamaria incredibilis sp. nov.

Tables 3, 4, Figs 3, 4, 5, 6

Type material.

Holotype. • SYS r 002596, adult male, from Nazhi Village (那支村), Aidian Town, Ningming County, Chongzuo City, Guangxi ZAR, China (21.8597°N, 107.0169°E; altitude 1060 m asl), collected by Shuo Qi on 25 April 2021.

Paratype (n = 1) • GEP r 093, adult male from Huaping National NR (花坪国家级自然保护区), Lingui District, Guilin City, Guangxi ZAR, China (25.6270°N, 109.9137°E; altitude 760 m asl), collected by Jian Wang, Zhao-Chi Zeng, and Hong-Hui Chen on 23 April 2025.

Diagnosis.

Calamaria incredibilis sp. nov. can be distinguished from all other congeners by the combination of the following morphological characters: nine 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; dorsal scales in 13–13 – 13 rows, smooth throughout; a single preocular and postocular; four supralabials, with the 2 nd and 3 rd ones contacting the eye; five infralabials; six scales surrounding the paraparietal; 170–182 ventrals in males; 21–23 paired subcaudals in males; a relatively short tail (8.2–8.4 % of total length in males), thick and nearly cylindrical, gradually tapering to an obtuse point; dorsal coloration brown, seven longitudinal series of interrupted dark brown stripes are visible along the body, extending from behind the collar to the tip of the tail; the margins of the dorsal scales are heavily suffused with black pigment, forming an almost reticulate pattern; the ventral surface yellowish white, with dark brown blotches along the outermost lateral margins; absence of light spots on the dorsal tail.

Description of the holotype.

SYS r 002596, adult male (see Fig. 3); specimen in good condition, slightly discolored due to preservation. Body slender, cylindrical (SVL 222.7 mm); tail short, slightly thinner than body, thick and nearly cylindrical, gradually tapering to an obtuse point (TaL 20.4 mm, TaL / TL 8.4 %). Head small, elliptical in dorsal view (head length 7.3 mm; head width 4.2 mm; head height 3.0 mm). Eye small, round (eye diameter 0.8 mm), eye-nostril distance 1.5 mm, eye-mouth distance 0.7 mm.

Head scalation. Rostral broader than high (rostral width 1.8 mm, rostral height 1.2 mm); dorsal portion visible from above approximately half the length of the prefrontal suture. Prefrontal shorter than frontal, not entering orbit, in contact with the first and second supralabials. Frontal hexagonal, longer than wide (frontal length 2.5 mm, frontal width 1.6 mm). Temporals absent. Paraparietal surrounded by six scales. One preocular on each side, higher than wide, slightly taller than postocular but shorter than eye diameter. One postocular on each side, also higher than wide. Nasals divided, small, bordered by rostral, prefrontal, and 1 st supralabial. Four supralabials on each side, the 2 nd and 3 rd entering the orbit; the 4 th is markedly larger than the other three (relative size: 4> 2> 3> 1). Five infralabials on each side, the first three pairs contacting anterior chin shields; the 1 st pair meeting at the midline; the 3 rd largest. Anterior chin shields much longer than wide, pentagonal, meeting at the midline. Posterior chin shields are longer, in contact anteriorly, and separated posteriorly by first gulars. Mental triangular, not in contact with anterior chin shields.

Body scalation. Dorsal scale rows 13–13 – 13 throughout body, all smooth. Ventrals 170 (+ 3 gulars); subcaudals 21, all paired. Cloacal plate undivided.

Coloration of the holotype. In life, the dorsal surface of head is brown, with blackish pigment forming a mask-like marking dorsally; the lateral surfaces of the head are slightly paler than the dorsum, with blackish pigment forming a longitudinal mask extending from the rostral region to the temporal region. The ventral surface of the head is yellowish white, with irregular dark brown blotches. The dorsal surface of the body is brown. Two nuchal collars are present, the first is a distinct dark brown collar, slightly shorter than the head length and extending laterally onto the sides of the neck; the second is smaller, pale, pattern-less, and approximately one to two dorsal scales in length. Seven longitudinal series of interrupted dark brown stripes are visible along the body, extending from behind the pale-colored collar to the tip of the tail. The margins of the dorsal scales are heavily suffused with black pigment, forming an almost reticulate pattern. The ventrals are pale yellow, with dark brown blotches along the outermost lateral margins, forming a dashed line parallel to the longitudinal stripes. The tail dorsum is slightly darker than the body dorsum, and the longitudinal stripes fade posteriorly. Light spots are absent on the dorsal tail. Subcaudal surface pale yellow, generally immaculate with only a few scattered dark pigment blotches.

In preservative, the head, body, and tail dorsum fade to dark brown. Two nuchal collars remain in strong contrast. The dark brown longitudinal stripes become much more diffuse, whereas the reticulate pattern formed by the heavily pigmented margins of the dorsal scales becomes more conspicuous. The ventral surfaces of the head, body, and tail are generally pale white, only with tiny dark speckles on the ventral surfaces of tail.

Skull morphology of holotype (Fig. 4). The skull is subcylindrical in general shape. In dorsal view, the anterior margin of the premaxilla is flat, the nasals and septomaxillae are relatively strong and laterally expanded, the conchal processes of the septomaxillae are broad, flattened, and well-developed. The frontals are approximately right-triangle-shaped with their anterior tip rounded. The parietal is scutiform, longer than wide. The supraoccipital, preoccipital, and exoccipitals are fully fused into a complex that forms the widest part of the braincase.

In ventral view, the vomers are well-developed with their anterior tips nearly reaching the vomerine processes of premaxilla. The maxillary processes of palatines are triangular and laterally expanded while the choanal processes. The pterygoid is slender and lanceolate in shape, twice the length of the palatine. The basisphenoid and basioccipital lack a ventral process. The parasphenoid rostrum of the basisphenoid is sharp and triangular-shaped. The basioccipital is relatively flat and laterally expanded.

In lateral view, the ascending process of premaxilla is slender and greatly reduced. The conchal process of the septomaxillae is anteroposteriorly expanded, reaching the lateral edge of nasals. The prefrontal and postorbital are similar in height, the bottom tip of the postorbital reaches the top margin of the maxilla. The ectopterygoid is biforked, the labial furcula of ectopterygoid is oval, and distinct from the lingual process. The lingual process projects anterodorsally, overlaps the dorsal margin ectopterygoid process of the maxilla, visible in lateral view but invisible in ventral view.

The mandible is slender and moderately curved. The prearticular crest of the compound bone is prominent while the surangular crest is absent.

Dentition of the holotype (Fig. 4). The maxillary teeth are laterally compressed, reduced in number, with their distal tip posteriorly recurved. The morphology of palatine teeth, pterygoid teeth, and dentary teeth show no significant specialization relative to the maxillary teeth. Maxillary teeth 9, palatine teeth 6, pterygoid teeth 10 / 11, dentary teeth 8 on each side.

Variation

(Figs 5, 6). Variation in measurements and scalation of the type series is summarized in Table 3. The two specimens are generally similar in overall appearance. However, in the paratype, the posterior portion of the ventral surface is slightly darker, being pale yellow compared to the yellowish white anterior portion. In addition, the ventral scales are scattered with more tiny dark speckles than in the holotype.

Source: 1 = Fan (1931); 2 = Wu et al. (1985); 3 = This study.

Etymology.

The specific epithet incredibilis is a Latin adjective meaning “ unbelievable ” or “ extraordinary, ” referring to the unexpectedly high level of cryptic diversity revealed by the discovery of this species, particularly in relation to closely allied taxa within the C. pavimentata species complex and their close geographic proximity. Based on the type locality, we propose the following common names: “ Guangxi Reed Snake ” (English), 广西两头蛇 (guǎng xī liǎng tóu shé, Chinese), “ R ắn mai g ầm qu ảng tây ” (Vietnamese), and Гуанси ́ йская карликовая змея (Guansiyskaya karlikovaya zmeya, Russian).

Comparison.

Comparative morphological data for Calamaria incredibilis sp. nov. and currently recognized members of the genus Calamaria from mainland China and the Indo-Burma Region are summarized in Table 4.

Calamaria incredibilis sp. nov. is readily distinguished from the nearly sympatric species C. jinggangensis and C. similis by a unique combination of morphological characters. It differs from C. jinggangensis by having more ventral scales in males (VEN 170–182 vs. 157–158); more subcaudal scales in males (SC 21–23 vs. 20); a markedly shorter relative tail length in males (TaL / TL 8.2–8.4 % vs. 15.0 %); a yellowish-white ventral surface (vs. dark orange); dark brown pigmentation along the lateral margins of the ventrals (vs. immaculate); and by the absence of a light blotch at the vent and two light blotches on each flank near the distal portion of the tail (vs. present). Calamaria incredibilis sp. nov. differs from C. similis by having more ventral scales in males (VEN 170–182 vs. 145–155); the absence of a light blotch at the vent and two light blotches on each flank near the distal portion of the tail (vs. present).

Moreover, Calamaria incredibilis sp. nov. differs from C. pavimentata sensu stricto (Java Island, Indonesia) by having more ventral scales in males (VEN 170–182 vs. 151); fewer subcaudal scales in males (SC 21–23 vs. 27); and a markedly shorter relative tail length in males (TaL / TL 8.2–8.4 % vs. 11.6 %). In addition, Calamaria incredibilis sp. nov. can be distinguished morphologically from the six junior synonyms or subspecies historically assigned to C. pavimentata. It differs from Calamaria siamensis by having a lower maximum number of ventral scales in males (VEN up to 182 vs. 190) and by the presence of a distinct pale nuchal collar (vs. absent or indistinct). It further differs from Calamaria pavimentata var. uniformis by having more ventral scale counts in males (VEN 170–182 vs. 143–149) and fewer subcaudal scales in males (SC 21–23 vs. 30–34). From Calamaria pavimentata formosana, the new species differs by having a markedly shorter relative tail length in males (TaL / TL 8.2–8.4 % vs. 8.6–13.2 %). It differs from Calamaria pavimentata banaensis by having more ventral scale counts in males (VEN 170–182 vs. 157–160) and by lacking a dark midventral stripe on the belly (vs. present). Finally, Calamaria incredibilis sp. nov. differs from Calamaria pavimentata miyarai by having a pale nuchal collar (vs. absent or indistinct).

Calamaria incredibilis sp. nov. is readily distinguished from C. lumbricoidea and C. schlegeli by having four supralabials, with the second and third in contact with the eye (vs. five supralabials, with the third and fourth in contact with the eye). Furthermore, both species are restricted to areas south of the Isthmus of Kra in Peninsular Malaysia and have not been recorded from mainland Indochina. Calamaria incredibilis sp. nov. also differs from C. lovii ingermarxorum, C. nebulosa, C. thanhi and C. yunnanensis by the presence of a preocular scale (vs. absent). It further differs from C. buchi, C. concolor, C. gialaiensis, C. lovii ingermarxorum, C. lumbricoidea, and C. sangi in having the mental not contacting the chin shields (vs. contacting). In addition, Calamaria incredibilis sp. nov. differs from several other congeners distributed in mainland China and the Indo-Burma Region by having more ventral scales in males. Specifically, it can be distinguished from C. abramovi by having more ventral scales in males (VEN 170–182 vs. 159); from C. berezowskii (VEN 170–182 vs. 149–155); from C. garoensis (VEN 170–182 vs. 165); from C. mizoramensis (VEN 170–182 vs. 147–155); from C. septentrionalis (VEN 170–182 vs. 148–166); from C. strigiventris (VEN 170–182 vs. 130–168); and from C. synergis (VEN 170–182 vs. 161–166). Compared with Calamaria andersoni, Calamaria incredibilis sp. nov. has a tail gradually tapering posteriorly (vs. not tapering), yellowish-white ventral surfaces (vs. orange-yellow), and the presence of light blotches on the neck (vs. absent). Calamaria incredibilis sp. nov. differs from C. annamensis by having a slightly longer relative tail length in males (TaL / TL 8.2–8.4 % vs. 6.6 %), and yellowish-white ventrals (vs. light orange to salmon with small black spots). The new species can be distinguished from Calamaria arcana by having yellowish-white ventrals (vs. orangish-red), the presence of light blotches on the neck (vs. absent), and the absence of a light blotch at the vent and two light blotches on each flank near the distal portion of the tail (vs. present). Finally, Calamaria incredibilis sp. nov. is distinct from C. dominici by having a dorsal coloration reddish brown to dark brown with narrow dark longitudinal stripes (vs. dark with irregular yellow blotches), the presence of light blotches on the neck (vs. absent), and yellowish-white ventrals (vs. dark with a few yellow blotches and bands).

Distribution, natural history notes, and conservation.

Calamaria incredibilis sp. nov. is currently known from Ningming County, Chongzuo City, and Lingui District, Guilin City, Guangxi ZAR, China, with the two localities separated by more than 500 km, and is so far represented by only two specimens. Both specimens were collected during daytime surveys and were encountered on roads. Given the semi-fossorial habits of this species, it is likely to have a broader distribution within Guangxi. In addition, because the holotype was collected near the China-Vietnam border, we further hypothesize that this species may also occur in the Mau Son Mountain, Lang Son Province, northern Vietnam. At present, due to the very limited number of confirmed records and the lack of information on population size, trends, and threats, we recommend that Calamaria incredibilis sp. nov. be provisionally assessed as Data Deficient (DD) under the IUCN Red List criteria.