Rhabdophis hmongorum, Kane & Tapley & La & Nguyen, 2023

Kane, Daniel, Tapley, Benjamin, La, Toi Van & Nguyen, Luan Thanh, 2023, A new species of the genus Rhabdophis Fitzinger, 1843 (Squamata: Colubridae) from the Hoang Lien range, northwest Vietnam, Zootaxa 5343 (2), pp. 101-125 : 112-120

publication ID	https://doi.org/ 10.11646/zootaxa.5343.2.1
publication LSID	lsid:zoobank.org:pub:EAE5AAAB-4DDE-4FA6-AF24-9D9937C194B2
DOI	https://doi.org/10.5281/zenodo.8329585
persistent identifier	https://treatment.plazi.org/id/AF771372-F763-FFF6-FF0A-F9D2FDAA4EF7
treatment provided by	Plazi
scientific name	Rhabdophis hmongorum
status	sp. nov.

Treatment

Rhabdophis hmongorum sp. nov.

( Figs. 1–7 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 ; Tables 1 View TABLE 1 & 4 View TABLE 4 )

Chresonymy. Rhabdophis sp. in Che et al. (2020)

Holotype. ITBCZ 3616 (Field tag LNT 0562), a male specimen ( Figs. 1–7 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 ), collected by Chang A Sung and Pao A Vang from Mount Fansipan , Hoang Lien National Park, Sa Pa District, Lao Cai Province, Vietnam (22.320588 N, 103.770308 E, 2602 m elevation; Fig. 8 View FIGURE 8 ) on June 28, 2022, at 1300 hrs as it moved close to a shallow stream in disturbed secondary forest. GoogleMaps

Diagnosis and identification. The new species is assigned to the genus Rhabdophis based on the following morphological traits: two enlarged maxillary teeth, not preceded by a diastema, positioned at the rear of the bone ( Fig.3 A–B View FIGURE 3 ); head distinct from neck; nostrils directed laterally; typical generic arrangement of nine dorsal cephalic scales; internasal scales truncated on anterior edge; eye relatively large with rounded pupil; anal scale divided.

Rhabdophis hmongorum sp. nov. differs from its congeners by a unique combination of the following characters: (1) 17-17-15 dorsal scale rows; (2) ventral scales 151; (3) subcaudal scales 59; (4) nostrils located laterally on head; (5) internasal scales truncated anteriorly; (6) nuchal groove present; no enlarged nuchal scales; (7) subcaudal scales paired; (8) first row of body scales smooth from head to neck, becoming progressively more keeled toward the tail; (9) dorsal scales keeled, with uppermost 5 rows strongly keeled; (10) posterior two maxillary teeth enlarged, not preceded by a diastema; (11) maxillary tooth count 25 (23+2); (12) short and bilobed hemipenes, extending to 13 th subcaudal scale, with spines on both lobes and at base.

Description of holotype. See Table 1 View TABLE 1 and 4 View TABLE 4 for morphometric and meristic data and comparisons with all other currently described species of Rhabdophis . Holotype is male, presumed adult on account of general proportions; body in cross section ( Figs. 1 View FIGURE 1 , 2A–B View FIGURE 2 ; 4A–C View FIGURE 4 ) appears oval in shape from neck to tail, widest at midbody, tapering toward tail which ends in a single pointed scale ( Figs. 2A–B View FIGURE 2 ; 4B–C View FIGURE 4 ); ventral surface flat ( Figs. 2B View FIGURE 2 ; 4C View FIGURE 4 ), angulate laterally; head longer than broad, wider than neck, head height highest between eyes, widest at level of parietal scales, ovate in lateral view, top of head flat, gently rounding to near vertical laterally, snout truncated in dorsal view, rostral scale angled down and overhanging lower jaw; eyes lateral, relatively large, eye diameter less than distance from eye to nostril, pupil round ( Figs. 5A–C View FIGURE 5 ).

Paired head shields abut along midline and do not overlap; rostral broader than tall, with highest point protruding slightly between anterior internasals, projecting beyond lower jaw and only visible dorsally on border with internasals; internasals and prefrontals wider than long; prefrontals wider and longer than internasals; frontal hexagonal and smaller than each parietal and as long as each supraocular, anterior midpoint not as strongly angled as posterior midpoint, frontal touching prefrontals, supraoculars and parietals; supraoculars almost twice as long as wide, though wider posteriorly than anteriorly; parietals approximately twice as large as frontal, approximately twice as wide anteriorly than posteriorly, extending to lateral aspects of the head; parietals contacting both postoculars, two temporals, three small nuchals, frontal and supraoculars ( Figs. 5A–C View FIGURE 5 ).

Nasal scale divided with opposing ‘c’ shapes of approximately equal size, with circular nostril present in centre; upper portion of nostril shallow, lower portion deep; nostril located closer to snout than to eye; loreal trapezoidal in shape, slightly wider at base than top, height approximately equal to width at base, touching posterior nasal, supralabials 2–3, preocular and prefrontal; supralabials 6/6, 5 th widest and tallest, 1 st contacting rostral and anterior and posterior nasals, 2 nd contacting posterior nasal and loreal, 3 rd contacting loreal, preocular and eye, 4 th contacting eye and lower postocular, 5 th contacting lower postocular and two temporals, 6 th contacting two posterior temporals; preoculars 1/1, upper portion touching supraocular, anterior margin contacting prefrontal and loreal, lower margin contacting 3 rd supralabial, posterior margin contacting eye; postoculars 2/2, bottom largest, top smallest; top postocular contacting supraocular, parietal and eye, bottom postocular contacting top postocular, parietal, temporal, supralabials 4–5 and eye; temporals 1+2 both sides, anterior temporal longer than tall, approximately half as long as 5 th supralabial, upper posterior temporal approximately equal in size to anterior temporal, lower posterior temporal approximately half the size ( Figs. 5A–C View FIGURE 5 ).

Mental subtriangular, broader than long, infralabials 7/7, 1–4 touching anterior chin shields, 4–6 touching posterior chin shields; anterior chin shields approximately half the length of posterior chin shields, anterior chin shields approximately half as wide as long, posterior chin shields approximately one quarter as wide as long; anterior-most ventral preceded by anterior-most first dorsal scale rows ( Fig. 4C View FIGURE 4 ).

Dorsal body scales all keeled ( Fig. 1 View FIGURE 1 ; 2A View FIGURE 2 ; Figs. 4A–B View FIGURE 4 ; Fig. 6 View FIGURE 6 ), aside from the lowest three rows on either side of the neck for approximately two head lengths posterior to the head, which are unkeeled. Lowest body scale rows have less well-developed keels than dorsal scales above. Tail dorsal scales heavily keeled; apical pits absent; lowest row of dorsal scales slightly wider than others; dorsal scale rows 17 at one head length behind the head; 17 at midbody; 15 at one head length cranial to the cloaca; ventral scales 151; cloacal scales paired; subcaudal scales 59, paired; terminal scute conical; tail subtriangular in cross section, flattened ventrally; SVL 409 mm; tail length 106 mm; mass following euthanasia and prior to fixation 38.7 g.

Hemipenis ( Figs. 7A–C View FIGURE 7 ). The right organ only was examined; organ is bilobed with small spines on both lobes and at base, with one large spine at base visible in sulcate view, spines arranged more densely toward tips and less dense but larger at base; calyces undifferentiated and not forming distinct capitulum; sulcus spermaticus bifurcated at level of lobe base, centripetal, sulcal lip inconspicuous. The tip of organ reached the level of the 13 th subcaudal scale.

Dentition ( Fig. 3 A–B View FIGURE 3 ; Table 1 View TABLE 1 ). Maxillary teeth 23+2, recurved, not compressed laterally; gradually increasing in size posteriorly; 8 th tooth is missing from maxilla, though socket is present; no diastema present, last two teeth distinctly enlarged.

Colouration in life ( Fig. 1 View FIGURE 1 ; Figs. 4A–C View FIGURE 4 ; Figs. 5 A–C View FIGURE 5 , Fig. 6 View FIGURE 6 ). General colour of dorsum is purplish grey with distinct iridescence; eye pupil is black, iris copper coloured on uppermost third, darker bronze on lower two thirds; indistinct orange line is present from the lower margin of the orbit following the junction between supralabial scales 4–5; supralabial scales 1–5 grey on lower areas; suffused orange pigment present laterally on supralabial scale 6 and lower three dorsal scale rows for approximately one head length caudal to the head; chin greyish white; venter iridescent along entire length; greyish white anteriorly, darkening to become greyish orange toward midbody and through to tail tip; areas of darker pigment present along ventral midline from approximately midbody to cloaca; posterior margins of subcaudal scales edged with dark grey colour.

Colouration in preservative ( Figs. 2A–B View FIGURE 2 ). Coloration in preservative is similar to when alive, though at the time of writing the holotype specimen has been in preservative for five months.

Etymology. The specific name is a patronym for the H’Mong people, an ethnic minority people in the northwest montane regions of Vietnam. Their assistance made it possible for us to collect the type specimen of the new species in the montane forest of Lao Cai Province, northwest Vietnam.

Suggested vernacular name. We recommend ‘H’mong keelback’ as the common English name and ‘Rắn hoa cỏ H’mông’ as the Vietnamese name.

Comparison. See Table 1 View TABLE 1 for differentiation of Rhabdophis hmongorum sp. nov. with congeners. Rhabdophis hmongorum sp. nov. can be distinguished from all species in the genus Rhabdophis based on morphology, and from all species for which comparable molecular data are available. A multi-access key for the genus Rhabdophis is available in supplementary file S1.

Dorsal scale rows. Rhabdophis hmongorum sp. nov. differs in having 17 scale rows at midbody (versus 23–27 in R. plumbicolor ; 21 in R. callistus and R. chrysargoides ; 19 in R. adleri , R. akraios , R. bindi , R. callichroma , R. ceylonensis , R. chrysargos , R. confusus , R. conspicillatus , R. flaviceps , R. formosanus , R. helleri , R. himalayanus , R. lateralis , R. lineatus , R. murudensis , R. nigrocinctus , R. rhodomelas , R. siamensis , R. subminiatus , and R. tigrinus ; 15 in R. angeli , R. chiwen , R. guangdongensis , R. nuchalis , R. pentasupralabialis , and R. swinhonis ).

Subcaudal scale rows. Rhabdophis hmongorum sp. nov. differs in having a greater number of subcaudals (59) (versus 35–50 in R. plumbicolor , 39 in R. guangdongensis , 39–46 in R. angeli , 40–53 in R. conspicillatus , and 48–54 in R. ceylonensis ) and differs from the following species in having fewer subcaudals (59) (versus 60–93 in R. chrysargos , 63–97 in R. murudensis , 64–79 in R. chrysargoides , 65–89 in R. siamensis , 66–71 in R. lineatus , 71–93 in R. auriculatus , 73–88 in R. adleri , 75–92 in R. barbouri ), 75–97 in R. helleri , 76 in R. callistus , 76–102 in R. bindi , 79–86 in R. callichroma , 80–97 in R. nigrocinctus , 82–88 in R. himalayanus and 85–88 in R. formosanus .

Ventral scales. Rhabdophis hmongorum sp. nov. differs in the number of ventrals being 151 (versus 117–126 in R. angeli , 120–138 in R. flaviceps , 126 in R. guangdongensis , 128–138 in R. rhodomelas , 132–142 in R. lineatus , 132–145 in R. subminiatus , 133–141 in R. ceylonensis , 138–147 in R. conspicillatus , 154–161 in R. chrysargoides , 156 in R. callistus , 157–178 in R. helleri , 157–164 in R. bindi , 163–171 in R. formosanus , 165–171 in R. himalayanus , 167–184 in R. akraios , and 176–185 in R. murudensis .

Maxillary teeth. Rhabdophis hmongorum sp. nov. differs in the number of maxillary teeth being 25 (23+2) (versus 17 in R. akraios , 18 in R. lineatus and R. pentasupralabialis , 18–22 in R. nuchalis , 18–19 in R. leonardi , 19–23 in R. swinhonis , 20 in R. guangdongensis , 20–21 in R. lateralis , 20–22 in R. flaviceps , 23 in R. murudensis , 26 in R. himalayanus , 26–29 in R. bindi , 27 in R. adleri , 27–32 in R. auriculatus , 27–35 in R. callichroma and R. chrysargos , and 28 in R. nigrocinctus .

Hemipenis. The hemipenis of Rhabdophis hmongorum sp. nov. has a large spine at the base, similar to R. bindi ( Das et al. 2021) , R. guangdongensis ( Zhu et al. 2020) and R. tigrinus ( Cadle, 2011) , as opposed to not having a spine present at base of hemipenis as reported for R. chiwen ( Piao et al. 2020) .

Similarities. Rhabdophis hmongorum sp. nov. appears superficially most similar to R. leonardi though can be distinguished by maxillary tooth count (25 in R. hmongorum sp. nov. versus 18–19 in R. leonardi ; Table 1 View TABLE 1 ) and by all mid body dorsal scale rows being keeled in R. hmongorum sp. nov. compared to the first 1–5 dorsal scale rows being unkeeled in R. leonardi ( Yang et al. 2023) . The description of Natrix nivalis ( Schmidt, 1925) mentions many characteristics which overlap with R. nuchalis , the species with which it is currently synonymised. Furthermore, this description presents several traits which overlap with other species in the nuchalis group, including R. hmongorum sp. nov ( Table 1 View TABLE 1 ). Given the lack of genetic information available from the specimen from which N. nivalis was initially described, we follow current taxonomy and include N. nivalis here as a junior subjective synonym of R. nuchalis , pending more detailed analysis. Additional further historic confusion within the R. nuchalis group is presented by Yang et al. (2023), highlighting the need for robust data and documentation relevant to taxonomic work.

Distribution, natural history and conservation status. The holotype specimen was collected on Mount Fansipan, northwest Vietnam ( Fig. 8A View FIGURE 8 ) in disturbed secondary broadleaf/upper montane forest ( Fig. 8B View FIGURE 8 ). The holotype specimen was encountered moving during the day along a dry streambed approximately 1–2 m wide. This species is currently only known from a single specimen from the Hoang Lien National Park at an elevation of 2602 m, and from a single specimen collected in Yunnan, China. Despite survey effort in north-western Vietnam, at this location, at different times of the year (March, April, June, September and December), the species has been encountered once (when collected). The high-elevation site where Rhabdophis hmongorum sp. nov. occurs faces the immediate threat of habitat degradation; the forest in which this species occurs is being negatively impacted by fuelwood collection for the tourism industry and by the grazing of livestock. If Rhabdophis hmongorum sp. nov. is restricted to high elevations, it is likely that this species may be vulnerable to future climate change. Rhabdophis hmongorum sp. nov. is likely to be threatened by local persecution; both venomous and non-venomous snakes are routinely killed when they are encountered by people in Hoang Lien National Park. We recommend that Rhabdophis hmongorum sp. nov. is listed as Data Deficient in accordance with the IUCN Red List of Threatened Species categories and criteria ( IUCN, 2012).