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Rhabdops aquaticus GIRI, DEEPAK, CAPTAIN & GOWER, 2017

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Higher TaxaColubridae (Natricinae), Colubroidea, Caenophidia, Alethinophidia, Serpentes, Squamata (snakes)
Common NamesE: Water Rhabdops, Aquatic Rhabdops 
SynonymRhabdops aquaticus GIRI, DEEPAK, CAPTAIN & GOWER 2017 
DistributionIndia (S Maharashtra, N Karnataka), elevation 750–1000 m.

Type locality: Amboli, Sindudurg district, Maharashtra, India (15.955801° N, 73.997517° E; 745 m)  
TypesHolotype: NCBS AU163 (Figs. 3, 4), mature female, collected by Varad B. Giri, Swapnil Pawar and Akshay Khandekar on 15.vii.2015. Paratypes (n = 7). All males. Heads figured in Fig. 5. BNHS 1724, Koyna, Satara District, Maharashtra, P.W. Soman, 1.xi.1962; BNHS 3234, Humbarli, Koyna, Satara District, Maharashtra (N 17.410446, E73.726732, 940 m), V.B. Giri, 18.ix.2003; BNHS 3235, Humbarli, Koyna, Satara District, Maharashtra, I. Agarwal, V.B. Giri, I. Kehimkar, 13.vii.2004; BNHS 3347, Amboli, Sindhudurg District, Maharashtra, S.A. Chougule, ii.1986; BNHS 3509 and 3510, Amboli, Sindhudurg District, Maharashtra, V.B. Giri, ix.2009; NCBS AU162, Baraki, Kolhapur District, Maharashtra (N 16.748433, E 73.850155, 975 m), V.B. Giri and Swapnil Pawar, 20.viii.2014. 
DiagnosisDiagnosis. A Rhabdops with paired internasals and prefrontals, a mostly pale (yellow or whitish) venter with a dark, clearly demarcated irregular midventral stripe and more than 222 ventral scales. Beyond number of ventrals, pattern and colour, Rhabdops aquaticus sp. nov. differs from its most similar congener, R. olivaceus, also in nuclear and mitochondrial DNA sequences. See below for a detailed account of colour and pattern differences.

Comparisons: Rhabdops aquaticus sp. nov. is distinguished clearly from the northeast Indian R. bicolor in that the latter has a single (rather than paired) internasal and a single prefrontal. The two species also differ in colour pattern, in that R. bicolor lacks the prominent dark spots of R. aquaticus sp. nov. Rhabdops aquaticus sp. nov. is very similar to R. olivaceus in overall phenotype, including details of scalation (Tables 2, 3; Figs. 7,8). Our recognition of R. aquaticus sp. nov. as distinct from R. olivaceus is based on substantial and concordant discontinuity in variation in geography, DNA sequences, number of ventrals, pattern and colour. Among the vouchers that we have examined, R. aquaticus sp. nov. has more ventral scales than R. olivaceus (224–230, mean 227, SD = 3.94, n = 9 versus 205–217, mean 211, SD = 5.92, n = 8). There are also differences in subcaudal counts (Tables 2, 3), with male R. aquaticus sp. nov. having 75–81 and male R. olivaceus 65–74. Uncorrected mt p-distances between R. aquaticus sp. nov. and R. olivaceus are as follows: 16s 1.5%, nd4 4.2–4.9%, cytb 7.6–7.7%.
The most immediately obvious external phenotypic difference between Rhabdops aquaticus sp. nov. and R. olivaceus lies in the pattern and colour (Fig. 6 & 7). In large (presumably adult) R. aquaticus sp. nov., there is an abrupt demarcation between the darker dorsum and pale venter, with substantial ventrolateral, largely unblemished pale bands bordering a typically narrower and irregular dark midventral stripe, and parts of the supralabials and most of the underside of the head are pale. In R. olivaceus, in contrast, the supralabials, underside of the head and body are primarily darkly pigmented (Fig. 7b), there are no substantial pale patches, and along the body the dark dorsum ends ventrolaterally at least two narrowly separated, subparallel, narrow dark lines (shared by the lateral edges of the ventrals and lower edges of first dorsal scale row, and the upper edges of the first and bottom edges of the second dorsal scale row: Fig. 7). Dark spots on the dorsal scale rows in R. aquaticus sp. nov. are typically larger. Larger (presumably adult) R. aquaticus sp. nov. have conspicuously red-orange eyes (Figs. 6, 7a), unlike the only live specimen of R. olivaceus that we have seen a photograph of (Fig. 7b).
Considering all specimens that we have examined, R. aquaticus sp. nov. reaches a substantially larger total length than R. olivaceus (ca. 900 mm versus ca. 570 mm: Tables 2, 3). Ganesh et al. (2012) reported a 985 mm TL R. olivaceus, however, no specimen was collected, and it was from a locality in Karnataka state at the far northerly limit for vouchered records of the species (Fig. 1). In addition, this large specimen and one other uncollected animal from a nearby locality are reported as having more ventral scales (223 and 230) than known for R. olivaceus vouchers (205–217, see Table 3) and the larger specimen differs (S.R. Ganesh, pers. comm., 2017) from the colour and patterns documented here for R. olivaceus and R. aquaticus sp. nov. We suggest that the identity of the population(s) from Karnataka reported by Ganesh et al. (2012) requires closer investigation (which is already underway: S.R. Ganesh & Gowri Shankar, pers. comm., 2017). 
CommentSimilar species: R. aquaticus sp. nov. was previously mistakenly identified as R. olivaceus.

Behavior: chiefly nocturnal; docile when handled

Habitat: in lentic or very slowly flowing water on plateaus and in forest streams; During the day R. aquaticus sp. nov was found mostly under rocks close to streams or on plateaus, or basking on exposed rocks. 
EtymologyThe species name is derived from the Latin for relating to water, aquaticus, in reference to observations of this snake often being observed in freshwater bodies. For nomenclatural purposes, the species epithet is considered a noun in apposition. 
  • GIRI, VARAD B.; V. DEEPAK, ASHOK CAPTAIN, ABHIJIT DAS, SANDEEP DAS, K. P. RAJKUMAR, R. L. RATHISH, DAVID J. GOWER 2017. A new species of Rhabdops Boulenger, 1893 (Serpentes: Natricinae) from the northern Western Ghats region of India. Zootaxa 4319 (1): 027–052 - get paper here
  • LANGNER, C. 2018. Ergänzende Beobachtungen zum Aktivitätsrhythmus und zum potentiellen Beutespektrum der indischen Wassernatter Rhabdops aquaticus sowie zum Flucht­ver­halten der Kaulquappen von Indirana cf. semipalmatus. Sauria 40 (2): 65-70 - get paper here
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