Rhabdophis bindi, Das & Smith & Sidik & Sarker & Boruah & Patel & Deepak, 2021

Das, Abhijit, Smith, Eric N., Sidik, Irvan, Sarker, Goutam C., Boruah, Bitupan, Patel, Naitik G. & Deepak, V., 2021, Hidden in the plain sight: a new species of Rhabdophis (Serpentes: Natricinae) from the Rhabdophis himalayanus complex, Zootaxa 5020 (3), pp. 401-433 : 404-417

Rhabdophis bindi sp. nov.

( Figs. 1–7 , 9 ; Tables 2–3)

urn:lsid:zoobank.org:act:959B3FDA-9843-4544-8232-AC0370FD491C

Rhabdophis himalayanus: Rahman and Ahmed (2012:107) ; Purkayastha (2013:93); Hasan et al. (2014: 134); Hakim et al. (2020: 1255 , 1256)

Rhabdophis sp. : Das (2008: 24); Das et al. (2009:127,128); Mahony et al. (2009: 89); Das (2010).

Holotype. WII-AD632, (Figs 3,7), adult male, collected from Maruacherra (30 m elevation, 24.97354 N, 92767 E), Cachar District , Assam, India by Alex Pothmy on 14 April 2019.

Paratypes (n = 4). All from Cachar District , Assam, India. WII-AD45, adult male from Lakhicherra (55 m, 24.97635 N, 92.77700 E), found among tree root undercut close to a water puddle, 3 m away from dry streambed on 28 March 2007 at 1110h; WII-AD46, adult female from Marua Village (32 m, 24.97311 N, 92.76815 E), killed by local people on 2 April 2007 at 1630h; WII-AD48, adult male from Lakhicherra Stream (36 m, 24.97639 N, 92.78058 E), collected among accumulated vegetation 1.5 m away from flowing stream on 26 May 2007 at 1230h; WII-AD47, adult male from Jhum Cultivation field above Borthol Stream (100 m, 24.98411 N, 92.77526 E, on 26 May 2007 at 1730h.

Referred specimens (n = 6). BANGLADESH: Chittagong: ZSI 14579, female, from unknown locality in Chittagong collected by E. P. Stebbins; ZSI 14574, unsexed juvenile, from Kaptai (~ 30m, ca. 22.49133 N, 92.21993 E), collected by E. P. Stebbins. INDIA: Assam: Cachar District: WII-AD6239, adult female, from Maruacherra Stream (32 m, 24.974064 N, 92.770481 E), found among leaflitter 15 m away from flowing stream on 17 May 2008 ; WII- AD6235, adult female from Bijoypore (40 m, 24.954966 N, 92.770481 E), found among woody debris on a dry stream bed on 28 February 2011 at 1245h ; Mizoram: HT R217 , adult female collected from unknown location in Mizoram by H. T. Lalremsanga ; Tripura: WII-AD 6240, adult male, Rangamura, near Trishna WLS , Tripura (33m, 23.272404 N, 91.344944 E) .

Diagnosis. A medium-sized Rhabdophis (sensu stricto) characterized by having: (1) 19 dorsal scale rows at midbody; (2) 157–164 ventrals; (3) nostril located on lateral side of head; (4) internasal truncated anteriorly; (5) nuchal groove absent; (6) no enlarged nuchal scales; (7) a prominent red rhomboid spot on nape; (8) a black subocular stripe present; (9) dorsum brownish, mottled with black and white; two rows of white spots on 2–3 scales on either side (often on 3rd–5th dorsal scale rows), cream towards tail; (10) last two maxillary teeth strongly and abruptly enlarged, preceded by a diastema.

Description of holotype. See Table 2 for morphometric and meristic data; adult male in good condition, in preliminary moulting stage—eye milky white; an incision runs along the first row of scales, 14 mm long, and located 130 mm from snout tip; body in cross section, oval at midbody, subtriangular near neck, widest at midbody, tapering most posteriorly than anteriorly; venter flat, angulate laterally; head longer than broad, highest between eyes, gently converged anteriorly, distinctly wider than neck, ovate in dorsal view, with steep flanks; snout truncated in dorsal view, rounded in lateral view; nostril region slightly concave in dorsal view; eyes lateral, large, slightly longer than tall, diameter longer than eye to nostril distance, with rounded pupils; parietal region flat, gently sloping downwards towards rostrum.

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Paired head shields abut along midline, rather than overlapping; rostral C-shaped, notched anteriorly, mid-point height one third of width, projecting beyond lower jaw, not visible from top except for border with anterior internasal; internasals and prefrontals almost as long as wide; prefrontal longer and broader than internasal; frontal hexagonal, slightly smaller than each parietal, as long as supraoculars, posterior and anterior midpoints weakly angulate, touching prefrontals, supraoculars, and parietals; supraocular almost twice as long as wide; parietal almost twice as long as wide, mid-suture 2/3 parietal length; each parietal contacting frontal, supraocular, upper postocular, three or four scales on each side, and three small nuchal scales, posteriorly.

Complete nasal scale, pentagonal, divided into smaller anterior and larger posterior nasal; posterior nasal higher than anterior nasal, sub-pentagonal in shape; anterior nasal sub-quadrangular; external naris subcircular, large, upper portion shallow, lower portion deep, visible clearly in anterior view rather than dorsal; nostril located slightly closer to snout than to eye; loreal height equal to width at its base, subtriangular, touching posterior nasal, supralabials 2–3, preocular, and prefrontal; supralabials 8/8, 6 th widest, 7 th tallest, 1 st contacting rostral and anterior and posterior nasals, 2 nd contacting posterior nasal and loreal, 3 rd contacting loreal and preocular, 4 th touching eye, 5 th contacting eye and lower postocular, 6 th touching postocular and lower anterior temporal, 7 th touching lower anterior and posterior temporals; preoculars 1/1, upper portion reaching top of head but, separated from frontal, contacting supralabials 3–4, loreal, prefrontal and supraocular; postoculars 3/3, top largest, bottom smallest; top postocular touching supraocular, parietal, and upper anterior temporal; middle postocular touching anterior temporals; lower postocular touching supralabials 5–6 and lower anterior temporal; temporals 2+2, both sides, lower anterior temporal almost equal in size to combined upper anterior and posterior temporals.

Mental subtriangular, wider than long; infralabials 9/9, 1–4 touching anterior chin-shields; 4–5 touching posterior chin-shields; anterior chin-shields slightly shorter than posterior chin-shields, chin shield width subequal, anteriormost ventral preceded by two preventrals, before chin-shields, separated from posterior infralabial by three scales.

Body dorsal scales all keeled, first row faintly keeled anteriorly but distinctly towards tail; tail dorsal scales heavily keeled; dorsal scales above cloaca smaller than at neck, and heavily keeled; apical pits absent; outermost scale row slightly broader; dorsal scale rows 19 at level of ventrals 1–74, 18 from ventrals 75–85, 17 from ventral 86 to last ventral; loss of dorsal scale row 3 between ventrals 85–86; ventrals 161cloacal scale paired; tail subtriangular in cross section, flattened ventrally; subcaudals 91, all divided; terminal scute conical, longer than broad; SVL 500 mm; tail length 180 mm.

Coloration. Olive color above; supralabials 2–5 black edged, forming broad dash between 5 and 6; neck with light orange spot; small whitish spots dorsolaterally, throughout body; black edged series of lateral scales; chin region pale white; venter pale cream anteriorly, darker yellowish posteriorly; edge and ventrolateral margins of ventrals darker; subcaudals pale white anteriorly, mottled with black posteriorly, dark edged.

Dentition. Maxillary teeth 26+2, recurved and stout, not compressed, gradually increasing in size posteriorly, diastema present, last two distinctly enlarged ( Fig. 4a , Table 2).

Hemipenis (n = 4). WII-AD47, WII-AD632 (left & right organ); WII-AD48 (left organ); WII-AD 45 (right organ). The organs are bilobed, with small spines throughout, denser towards tips but, larger towards mid-base; one hook present on flank at organ base, large and curve tipped (e.g. Fig. 4b ); calyces undifferentiated and not forming a distinct capitulum; sulcus spermaticus bifurcated, centripetal, sulcal lip inconspicuous (e.g. Fig. 4c ).

Variation among paratypes. WII-AD47, 632, and WII-AD6240 have 2+2 temporals on each side; WII-AD46, 48, and HTR 217 have two anterior and three posterior temporals on each side; ZSI 14579 has the lowest number of temporals, 1+2 on each side; and AD/ BR 45 has 2+1 on the left and 2+2 on the right side. For infralabials, WII- AD632, 6235, 6239, and DU 2009 show 9 infralabials on each side; WII-AD45, 47, 48, and HTR217 show 10 on each side; WII-AD46 and ZSI 14579 show 9 on right and ten on left. There are 161 ventral scales on WII-AD632, 45, and 47; ZSI 14579 shows the lowest number, 156, and overall, the range in ventrals is 156–163. Among paratypes examined for dentition, WII-AD46 matched the type but, WII-AD45, WII-AD48, and WII-AD47 had slightly higher maxillary teeth counts, total variation 28–31 ( Table 2). Hemipenis examined in (WII-AD45, WII-AD48, WII-AD47) matches in overall appearance of the holotype (WII-AD632).

Colour in life. Dorsum dark brown, top of head uniform brown; anterior part of body dorsal scales are randomly edged with white and black, posterior part of dorsum with small lighter spots arranged along mid dorsal line; labials light brown, some parts paler than others, partially edged with black on the posterior margins; two thick black lines, one below eye and other from behind eye to the angle of jaw after which it is broken but runs almost two head length behind in some individuals; series of narrow white spots along the two sides of mid dorsum, brighter and irregular in the anterior half of the dorsal body, in posterior parts, those bright spots become cream coloured and more consistent often one two dorsal scales, these spots are arranged along a faint reddish brown line running throughout length of the dorsum up to half of the tail length, interstitial skin greyish, a scarlet coloured diamond shaped mark on the top of neck just after parietals; Irish silver, tongue black; ventral uniform white, outer edge of ventrals edged with black; subcaudals yellowish lightly sprayed with black.

Comparison. Rhabdophis bindi sp. nov. differs in having 19 scale rows at midbody (versus 23–27 in R. plumbicolor ; 21 in R. callistus and R. chrysargoides ; 17 in R. leonardi and R. auriculatus ; 15 in R. chiwen , R. pentasupralabialis , R. angeli , R. guangdongensis , R. nuchalis and R. swinhonis ). Rhabdophis bindi sp. nov. differs from these species in having a higher number of subcaudals 88–102 (versus 44–66 in R. akraios , 49–60 in R. flaviceps , 42–58 in R. rhodomelas , 35–50 in R. plumbicolor , 39–46 in R. angeli , 79–86 in R. callichroma and 40–56 in R. conspicillatus , 38–74 in R. tigrinus and 61–75 in R. lineatus ). Rhabdophis bindi sp. nov. differs in the number of ventrals being157–164 (versus 148–156 in R. spilogaster and 176–185 in R. murudensis ). Rhabdophis bindi sp. nov differs in the number of maxillary teeth 28–31 (versus 27 in R. adleri , 24–26 in R. ceylonensis , 20–22 in R. flaviceps , 22–23 in R. angeli , 14–17 in R. rhodomelas ,> 33 in R. barbouri and in 22–23 R. tigrinus ). Rhabdophis bindi sp. nov. differs in overall dorsal body coloration brownish body without any distinct bands Versus dorsal body coloration green with distinct continuous/broken bands along the body in R. nigrocinctus .

Rhabdophis bindi sp. nov. shows some similarity with R. subminiatus and R. himalayanus and R. chrysargos (Appendix 3). Rhabdophis bindi sp. nov. can be easily distinguished from R. subminiatus including its subspecies R. subminiatus subminiatus Schlegel, 1837 and R. subminiatus helleri (Schmidt, 1925) by the presence of a diastema on the maxillary between the last two enlarged teeth and the rest of the tooth which is absent in R. subminiatus . Rhabdophis bindi sp. nov. (average SVL 537 mm, N = 10) can be distinguished from R. himalayanus (average SVL 621mm, N = 41) in having a smaller body size (Appendix 3) and the absence of nuchal glands. Furthermore, these two species can be differentiated clearly based on colour; Rhabdophis bindi sp. nov. have a plain venter and subcaudals versus venter and subcaudals mottled/dark with brownish or black coloration and it has a distinct roughly rhomboidal red spot whereas R. himalayanus has a band on its neck ( Figs. 6–8 ; Appendix 3). Rhabdophis bindi sp. nov. can be distinguished from R. chrysargos in having eight supralabials versus nine (Appendix 3). Furthermore, R. bindi sp. nov. can be distinguished from all other species of Rhabdophis except some populations of R. spilogaster in having a distinct roughly rhomboidal red coloured nuchal spot/blotch which is absent from all other species.

Etymology. The species epithet, “bindi, is an invariable feminine noun derived from the Sanskrit word ‘bindu’ (meaning a bright spot), referring to the unique “red marking on the nape region of the new species and reminiscent of the “red beauty spot adorning the foreheads of Indian women and signifying the point of creation of the cosmos.

Suggested English common names. Bindee keelback snake.

Distribution. Currently Extent of Occurrence of R. bindi sp. nov. is 12,950 km 2 covering India and Bangladesh. In India the species was recorded from Maruacherra and Lakhicherra localities close to foothills of areas of Barail Hill Range and within the drainage of Jatinga river in Southern Assam. The new species is also recorded from the bordering region of Assam and Mizoram and northern Tripura. Elsewhere this species was reported as R. himalayanus from Sylhet division Maulavibazar District, Sreemangal and Lawachara National Park ( Hakim et al. 2020). Historically the species was collected from Kaptai, Chittagong, Bangladesh. All specimens were collected between 27 m and 100 m elevation, hinting that the species prefers low elevations.

Natural history. Rhabdophis bindi sp. nov. appears to be a denizen of lowland evergreen forest corresponding to Cachar Tropical Evergreen Forest 1B/C3 and Cachar Tropical Semi-evergreen Forest 2B/C2 ( Champion & Seth 1968). The main secondary landscape elements are cultivated, extensive brakes of monopodial bamboo ( Melocanna sp. ) and clusters of sympodial bamboo ( Dendrocalamus sp. ), tree plantations ( Tectona grandis and Gmelina arborea ), secondary and disturbed forest (e.g. betel vine plantations), and village gardens.

The climate of the topotypic location is largely tropical with high precipitation and a brief but predictable rainless period (January–March). The annual rainfall varies from 2000 mm to more than 6000 mm. The Lakhicherra stream, from where multiple individuals of the new species were found is a third order evergreen forest stream. During the dry season (January–March; Fig. 9A ) the stream bed gets considerably dried up, although deep sections of the stream hold water in the form of pools. The dry stream bed with bedrocks and bryophyte covered boulders holds the moisture. This species seems to be active from the initial few showers that the area gets during April. At that time sudden water flow creates extensive piles of accumulated vegetation along or away from the stream bed. Two individuals were found under such accumulated vegetation. Amphibians such as Hydrophylax leptoglossa and Humerana humeralis were also found under such accumulated vegetation during day time. During May–June the region received heavy rainfall and with gushing water in the stream ( Fig. 9B ), individuals were encountered away from the streambed close to water puddles or on elevated moist slopes above the stream. The species is active during day time, however one individual was found active during dusk. In Bangladesh, one individual was sighted emerging from the water and crawling into grass by a railway line ( Mahony et al. 2009).

We recorded a gravid female in the month of May. The female (SVL 453 mm) had three eggs with the dimension of 11.50 x 5.27 mm. One individual was observed feeding on Euphlyctis cf. cyanophlyctis and another regurgitated a partially digested Hydrophylax leptoglossa . One individual tried to hide its head in the body coil while being photographed. All individuals were docile and never attempted to bite while handling. The largest male individual broke its tail while handling, a phenomenon reported in Xenochrophis ( Ananjeva & Orlov, 1994) and observed by one of us in field in Rhabdophis subminiatus , Amphiesma stolatum and Fowlea piscator (pers. Obs. AD). Photographic records show that this species have defensive displays similar to other Rhabdophis species (https://www. inaturalist.org/observations/44447569) where their head and anterior body is flattened.

Figures

FIGURE 1. ML phylogeny showing relationships of the newly sampled Rhabdophis (in blue) with sequences of other available congeners. Nuchal gland trait mapped to the tips. ML bootstrap support and BI posterior probability support =/>75 or 0.75 is shown at each internal branch.

FIGURE 2. Distribution of Rhabdophis bindi sp. nov. and R. himalayanus in India and Bangladesh. Localities are as follows: 1. Sikkim, 2. Rhi-Bhoi, 3. Maruacherra, 4. Lawacherra 5. Mamit, 6. Trishna and 7. Kaptai. Type localities are marked with an arrow.

FIGURE 3. Rhabdophis bindi sp. nov. holotype (WII-AD632). A. full body dorsal, and B. ventral view, C. head dorsal, D. ventral, and E–F. lateral views of head. Scale bars 10mm.

FIGURE 4. Rhabdophis bindi sp. nov. A. left maxilla (WII-AD48), B. hemipenis showing asulcal and C. sulcal region (WII- AD48). Scale bars 5mm.

FIGURE 5. Rhabdophis bindi sp. nov. A. WII-AD632 (holotype), B. WII-AD48 (paratype), C. WII-AD47 (paratype), D. WII-AD6240 (Referred), E. WII-AD46 (paratype) F. WII-AD45 (paratype), G. HT R217 (referred specimen), H. ZSI 14574 (referred specimen) I. ZSI 14579(referred specimen). Scale bars 10mm, G–I images not to scale.

FIGURE 6. A. Rhabdophis bindi sp. nov. (WII-AD47) from Lakhicherra, Cachar, Assam, B. Rhabdophis himalayanus (WII- AD396) from Sikkim. Inset image of the same specimens showing presence of nuchal gland (some are indicated with black arrowheads) in the latter species which is absent in the former. Images not to scale

FIGURE 7. A. Rhabdophis bindi sp. nov. male holotype in life (WII-AD632; 500 mm SVL). B. Rhabdophis chrysargos, female in life, from western Java (UTA R-62893; 596 mm SVL). Image not to scale.

FIGURE 8. Rhabdophis himalayanus specimens at the Natural History Museum, London: A. BMNH 1925.9.17.5 (type of Natrix speciosus), B. BMNH 1946.1.13.15 (syntype), C. BMNH 1946.1.23.75 (syntype) and D. BMNH 1946.1.15.27 (syntype of Xenodon macrophthalmus). Scale bars 50mm.

FIGURE 9. Habitat at the type locality of Rhabdophis bindi sp. nov. A. dry stream bed during February-April 2010 and B. during May 2010.