Lingnan Reed Snake (English), 岭南两头蛇 (Chinese)

KFBG 14611 (Figs 2, 3, 4, 5G–I, 6G–I), male, Mt. Dadongshan, Nanling National Nature Reserve, Lianzhou County, Qingyuan City, Guangdong Province, China (中国广东南岭国家级自然保护区大东山管理站). The specimen was found at between the hydroelectric station near Dadongshan Management Station (24°55’58.5”N 112°42’51.8”E) and Shizi Ping (石仔坪), 800–900 m above sea level, collected by Michael W.N. Lau on 7 July 2000 at 9:20 am.

The species epithet “arcana” is the nominative form the Latin adjective “arcanus” meaning “hidden”, “secret” and is given in feminine form to match the female genitive declension of the genus name Calamaria. It refers to the fact that this species is difficult to find with only a single specimen discovered during our long term survey in southern China. For common name we suggested as “Lingnan reed snake” in English and “Ling Nan Liang Tou She (岭南两头蛇)” in Chinese, referring to the Lingnan (岭南, means ‘South of the Nanling Mountains’) region where the new species is found. Lingnan is a geographic area referring to the lands in the south of the Nanling Mountains, covering the modern Chinese provinces of Guangdong, Guangxi and Hainan, as well as northern Vietnam.

Calamaria arcanasp. nov. is assigned to the genus Calamaria by its molecular phylogenetic position and the following morphological characters: dorsal scales in 13 rows throughout body, possessing elongate, cylindrical bodies, along with internasals and prefrontals fused, four supralabials and five infralabials (Inger and Marx 1965; Ziegler et al. 2008).

Calamaria arcanasp. nov. could be distinguished from all other species of Calamaria by the combination of the following characters: (1) ten modified maxillary teeth; (2) four supralabials, second and third supralabials entering orbit; (3) preocular present; (4) mental not touching anterior chin shields; (5) six scales and shields surrounding the paraparietal; (6) 170 ventral scales; (7) 22 paired subcaudals; (8) tail not gradually tapering, abruptly tapering at the tip; (9) dorsal scales reduced to five rows above last subcaudal at tail; (10) dorsum of body and tail brownish; (11) dark collar on nuchal region absent; (12) two outermost dorsal scale rows light yellow with upper margins partly dark pigmented; (13) ventral scales immaculate, without dark outermost corners and pigmentation anteriorly; and (14) absence of distinct dark longitudinal line or scattered spots on the underside of tail.

Male. Rostral wider than high (height 1.8 mm, width 2.2 mm), portion visible from above about equal to prefrontal suture; prefrontal shorter than frontal, not entering orbit, and touching first two supralabials; frontal hexagonal, about 2.2 times maximum width of supraocular; paraparietal surrounded by six shields and scales; a single preocular present, higher than postocular; postocular one, higher than wide, not as high as eye diameter; eye diameter 1.4 mm, larger than eye-mouth distance 0.8 mm; distance from anterior corner of eye to nostril 1.9 mm and to the tip of snout 3.1 mm; pupil rounded; supralabials 4/4 (left/right, hereafter), second and third entering orbit, fourth longest, third about 0.9 times of second in length, first shorter than third and as wide as second; mental semicircular to triangular, not touching anterior chin shields; infralabials 5/5, first three touching anterior chin shields; first pair of chin shields meeting in midline, second pair touching anteriorly and separated posteriorly by first gular scales; three gulars in midline between second chin shields and first ventrals; dorsal scales in 13 rows throughout body, reducing to eight rows above 3^rd subcaudal, to seven rows above 8^th subcaudal, to six rows above 10^th subcaudal, and to five rows above the last subcaudal on tail; ventral scales 170, subcaudals 22, divided, followed by a shield covering tail tip; anal scale single.

Head length 7.1 mm; head width 5.1 mm; SVL 281.5 mm; TaL 21.7 mm; TL 303.2 mm; body thickness about 5.8 to 6.4 mm; body thickness index at mid body 0.021; tail root 4.5 mm thick; tail not as thick as body, slightly tapering then abruptly tapering at tip; TaL/TL ratio 7.2%; maxillary teeth modified, 10/10.

Dorsal surface of body grey-brown above, somewhat iridescent; dark collar at nuchal region absent; indistinct light ring behind head present, nearly invisible; a narrow interrupted light ring at root of tail present, followed by few light spots on middle and tip of tail. Underside of head orangish-beige with black flecks on the infralabials; ventral scales of body and tail immaculate orangish-red, without dark pigmentation on outermost corners and anterior margins; underside of tail without dark longitudinal line or blotches.

Color preserved in ethanol fade to caramel-brown above. Dorsal head and upper parts of supralabials brown, lower parts of supralabials light yellow; underside of head light yellow with brownish spots on the infralabials; presence of an indistinct narrow yellow ring about 5 scales wide on neck, nearly invisible; dorsum of body caramel-brown, with light flecks on each dorsal scale; two outermost dorsal scale rows light yellow with upper margins partly dark pigmented; a narrow interrupted light ring at root of tail, light spots on middle and tip of tail still visible; ventral scales of body and tail uniformly light yellowish-beige; underside of tail without dark median line or blotches.

We compared Calamaria arcanasp. nov. with 18 congeners of the genus Calamaria from China and mainland Southeast Asia listed above. Unrelated taxa from the Greater Sunda Islands are omitted from comparisons for the sake of simplicity.

Calamaria arcanasp. nov. can be readily distinguished from C. albiventer, C. lumbricoidea, C. prakkei and C. schlegeli by having lower number of supralabials (four vs. five), and the pattern of supralabials shields touching the orbit (2^nd and 3^rd supralabials touching orbit vs. 3^rd and 4^th supralabials touching orbit). Additionally, these four species only occur south of the Isthmus of Kra in Peninsular Malaysia where is extremely far from the type locality of C. arcanasp. nov.

Calamaria arcanasp. nov. can be further easily distinguished with C. lovii, C. nebulosa, C. thanhi and C. yunnanensis by the presence of a preocular scale (vs. absence of preocular scale).

Calamaria arcanasp. nov. differs from C. abramovi by having eye diameter larger than distance from eye to mouth edge (vs. reverse condition in C. abramovi), posterior chin shields meeting in midline (vs. separated in C. abramovi), dorsal scales reduced to five rows at tail (vs. reduced to four rows in C. abramovi), and a distinctly different coloration (body black and with yellow-orange spots on venter in C. abramovi).

Calamaria arcanasp. nov. differs from C. andersoni by having dorsal scales reduced to five rows at tail (vs. reduced to four rows in C. andersoni), light color spots at root of tail present (vs. absent in C. andersoni. Fig. 6), ventral scales immaculate, without dark outermost corners (vs. presence of dark outermost corners on ventral scales in C. andersoni, Fig. 6), two outermost dorsal scale rows light yellow with upper margins partly dark pigmented (vs. all dorsal scale rows in same coloration in C. andersoni, Fig. 5).

Calamaria arcanasp. nov. differs from C. buchi by having rostral shield width larger than length (vs. reverse condition in C. buchi), eye diameter larger than distance from eye to mouth edge (vs. equal to or shorter in C. buchi), mental not touching anterior chin shields (vs. touching in C. buchi), dorsal scales reduced to five rows at tail (reduced to four rows in C. buchi), and six shields and scales surrounding paraparietal (vs. five in C. buchi).

Calamaria arcanasp. nov. differs from C. concolor by having lower number of supralabials (4 vs. 5 in C. concolor), eye diameter larger than distance from eye to mouth edge (vs. reverse condition in C. concolor), mental not touching anterior chin shields (vs. touching in C. concolor), tail not flatted (vs. slight flatted laterally in C. concolor), dorsal scales reduced to five rows at tail (vs. reduced to four rows in C. concolor), and lower number of ventral scales in males (170 vs. 209 in C. concolor).

Calamaria arcanasp. nov. differs from C. dominici by having dorsal scales reduced to five rows at tail (vs. reduced to four rows in C. dominici), absence of distinct yellow blotches on dorsum (vs. present in C. dominici), venter immaculate without any dark stripes or spots (vs. ventral side dark with yellow blotches and bands).

Calamaria arcanasp. nov. differs from C. gialaiensis by having mental not touching anterior chin shields (vs. touching in C. gialaiensis), lower number of ventral scales (170 in males vs. 191 in unknown gender), dorsal scales reduced to five rows at tail (vs. reduced to four rows in C. gialaiensis), absence of a dark longitudinal line under of tail (vs. present in C. gialaiensis), and absence of dark collar in nuchal region (vs. an indistinct dark collar present in nuchal region in C. gialaiensis).

Calamaria arcanasp. nov. differs from C. sangi by having mental not touching anterior chin shields (vs. touching in C. sangi), dorsal scales reduced to five rows at tail (vs. reduced to four rows in C. sangi), lower number of ventral scales (170 vs. 190 in C. sangi), absence of dark collar in nuchal region (vs. presence of dark collar in nuchal region in C. sangi), and venter immaculate (vs. venter cream with dark transverse bands in C. sangi).

Calamaria arcanasp. nov. differs from C. strigiventris by having eye diameter larger than distance from eye to mouth edge (vs. reverse condition in C. strigiventris), lower number of subcaudals in males (22 vs. 29–33 in males), higher number of ventrals in males (170 vs. 130–157), dorsal scales reduced to five rows at tail (vs. reduced to four rows in C. strigiventris), venter immaculate (vs. presence of three interrupted longitudinal black stripes in C. strigiventris).

Calamaria arcanasp. nov. differs from C. pavimentata by having rostral shield width larger than length (vs. reverse condition in C. pavimentata), tail slowly tapering anteriorly and abruptly tapering at tip (vs. tail tapering gradually to a point in C. pavimentata, Fig. 6), dorsal scales reduced to five rows at tail (vs. reduced to four rows in C. pavimentata), absence of dark collar at nuchal region (vs. present in C. pavimentata, Fig. 5), absence of distinct narrow and dark longitudinal lines on dorsum (vs. present in C. pavimentata, Fig. 5), absence of dark outermost corners on ventral scales (vs. ventral scales with dark outermost corners in C. pavimentata, Fig. 6).

Calamaria arcanasp. nov. can be distinguished from the sister taxon of C. septentrionalis by having tail abruptly tapering at the tip of end (vs. tail not tapering in C. septentrionalis), higher number of maxillary teeth (10 vs. 8–9 in C. septentrionalis), higher number of ventral scales in males (170 vs. 148–166 in C. septentrionalis), higher numbers of subcaudals in males (22 vs. 15–19 in C. septentrionalis), dorsal scales reduced to five rows at tail (vs. reduced to four rows in C. septentrionalis), absence of black line or spots on venter of tail (vs. venter of tail with broad and distinct median black stripe), absence of dark outermost corners on ventral scales (vs. present in C. septentrionalis, Fig. 6), two outermost dorsal scale rows light yellow with upper margins partly dark pigmented (vs. all dorsal scale rows in same coloration in C. septentrionalis, Fig. 5).

The holotype was found active on a cloudy morning along a trail in tall shrubland and secondary forest.

Calamaria arcanasp. nov. is currently only known from a single specimen from its type locality, Mt. Dadongshan, Nanling National Nature Reserve, Guangdong Province, China (Fig. 7). It can be expected that the new species should be distributed across adjacent mountain areas, but in view of the uncertainty of its extent of occurrence, and little information on its ecology and threats, we recommend the new species be listed as Data Deficient (DD) according the International Union for Conservation of Nature (IUCN) Red List categories and Criteria (IUCN 2022).