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Rhabdophis chiwen CHEN, DING, CHEN & PIAO, 2020

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Higher TaxaColubridae (Natricinae), Colubroidea, Caenophidia, Alethinophidia, Serpentes, Squamata (snakes)
Subspecies 
Common NamesE: Chiwen Keelback
Chinese: 螭吻颈槽蛇 
SynonymRhabdophis chiwen CHEN, DING, CHEN & PIAO in PIAO et al. 2020 
DistributionChina (Sichuan)

Type locality: Jiguan Mountain, Chongzhou City, Sichuan Province (30°45'57.64" N, 103°14'3.52" E, and 1846 m a.s.l.)  
Reproduction 
TypesHolotype. CIB116092, an adult male, collected on 1st July 2019 by Li Ding (Figure 2 and 3).
Paratypes. CIB116093, an adult male, collected from the same locality as holotype on 1st July 2019 by Li Ding. CIB116094- 95, two specimens, an adult male and an adult female, collected from Xingou Village, Tianquan County, Sichuan Province (29°55'42.39" N, 102°23'9.19" E, and 1461 m a.s.l.) collected on 22nd July 2018 by Li Ding and Zening Chen. 
DiagnosisDiagnosis. 1) nuchal groove present, with enlarged and paired scales on each side; 2) Dorsal body saddlebrown, DSR in 15 rows throughout, feebly keeled, the outer 1–2 rows smooth; 3) dorsal scales typically with black margins forming some spots and stripes, the margin of the outer row forming two faint dorsolateral black cross-bars alongside body; 4) a black oblique stripe below the eye, often with a black spot between the 2nd and 3rd SL and a black stripe (or separated as black spots) on the 5th SL and the 1st TEM; 5) Eyes dark khaki, pupils black; 6) SL 5, the 3rd and 4th touching the eye: 7) usually 7 ILs (occasionally 6 or 8), the first four contact with anterior chin-shields; 8) 1 LR, and TEM 1+1; 9) VEN 151-159, the outer margin of ventral scales and several lateral rows of dorsal scales forming ventrolateral longitudinal brownish-red coloration, with faint black spots in the middle of each ventral scale and between scales which line a black stripe; 10) anal divided; SC 45–59; 11) PRO 1 (rarely 2) and PTO usually 3 (occasionally 2); 12) medium-sized body (SVL of adult males: 404–431 mm and adult females: 409–476 mm); 13) tail moderate and longer in males than in females (adult males: 104-131 mm, adult females: 91–107 mm) (Chen et al. 2020).

Coloration of specimens in life. Dorsal body saddlebrown with rusty red. Dorsal scales are typically with black margins forming some scattered spots and stripes (for holotype, those dispersed black spots forming a black stripe around the neck, see Figure 3 A, C, E), the margin of the outer row forming two faint dorsolateral black cross-bars alongside body (Figure 2 A; Figure 5 A, C). Coloration of ventral is seashell and the outer margin of ventral scales and several lateral rows of dorsal scales forming ventrola teral longitudinal brownish-red colora tion, with faint black spots in the middle of each ventral scale and between scales at the anterior part of body which line a black stripe and merge into black patches covering the whole scale with dispersed brownish-red spots at the posterior part of body (Figure 2 B). Ha tchlings simila r to adults except for da rker dorsal coloration, a yellow stripe present on nape, separated by the nuchal groove (Figure 5 D); ventral scales typically shallow black (Chen et al. 2020).

Variation Other specimens generally resemble the holotype except the following characters (Table 1): IL rarely 8. PRO rarely 2 and PTO occasional 2. SVL ranges from 409–476 mm in females and 404–431 mm in males. Female specimens tend to have a shorter tail and fewer SC than male specimens (for TaL 91–107 mm versus 104–131 mm, for SC 45–52 versus 55–59). The ventrolateral longitudinal brownish–red coloration may be lighter (Figure 5 A, C) and faint black spots on the ventral scales could merge into la rge pa tches a nd cover the whole scale at the posterior part of body (Figure 5 B). The dorsal scales of some specimens (such as CIB116093) are feebly keeled even on the second outer row, with only the outer row smooth (Chen et al. 2020).

Comparisons Comparative data of R. chiwen with 27 known species of the genus Rhabdophis were obtained from literature (see Materials and methods) and are shown in Table 2.
Currently, 11 species are known to occur in China, and Rhabdophis chiwen can be distinguished from these species by following characters (a detailed comparison between R. chiwen and R. pentasupralabialis is separately listed in a latter paragraph). R. chiwen differs from R. adleri and R. himalayanus by DSR 15 rows throughout vs. DSR 19–19–17 in R. adleri and R. himalayanus. R. chiwen differs from R. formosanus and R. lateralis by DSR 15 rows throughout vs. DSR 19–19–17(15) in R. formosanus and R. lateralis. The new species differs from R. guangdongensis by 5 SLs, VEN 151–159, SC 45–59, dorsal body saddlebrown vs. 6 SLs, VEN 126, SC 39, brownish–grey coloration in R. guangdongensis. The new species is different from R. leonardi by DSR 15 rows throughout vs. DSR 18(17)–17–15 in R. leonardi. The new species is different from R. nigrocinctus and R. subminiatus by DSR 15 rows throughout vs. DSR 19–19–17 in R. nigrocinctus and R. subminiatus. The new species differs from R. nuchalis by 5 SLs, 7(6,8) ILs, TEM 1+1, dorsal body saddlebrown vs. 6 SLs, 8(7) ILs, TEM 1+2, olive green coloration with black and magneta spots in R. nuchalis (Figure 6). R. chiwen differs from R. swinhonis by 5 SLs, 7(6) ILs, dorsal body saddlebrown vs. 6 SLs, 8(7) ILs, medium brown coloration with several rows of black spots in R. swinhonis.
Rhabdophis chiwen, R. pentasupralabialis, R. guangdongensis, R. swinhonis, R. angeli and R. nuchalis have the minimal number of dorsal scale rows in this genus, equal to 15 rows. Nevertheless, R. chiwen can be readily distinguished from the other five species and all other species of Rhabdophis by SLs, DSR, VEN, SC, PRO, PTO or different coloration. Because R. guangdongensis, R. swinhonis and R. nuchalis are distributed in China, their comparisons with R. chiwen are listed in the previous paragraph. The new species differs from R. angeli by VEN 151–159, SC 45–59, dorsal body saddlebrown vs. VEN 117–126, SC 39–46, brownish coloration with a dorsolateral series of small reddish spots in R. angeli.
For the remaining species within the genus Rhabdophis except R. pentasupralabialis, R. chiwen sp. nov. can be readily distinguished by its dorsal scales in 15 rows throughout vs. DSR 17–17–15 in R. auriculata; DSR 19 at midbody in R. barbouri, R. callichromus, R. chrysargos, R. conspicillatus, R. lineatus and R. spilogaster ; DSR 21 at midbody in R. callistus and R. chrysargoides; DSR 19–19–15(17) in R. murudensis; DSR 19–19–17(15) in R. tigrinus.
Specimens collected from Xingou Village and Jiguan Mountain differ from specimens of R. pentasupralabialis by: 1) larger size (mean TL 536.83 mm) vs. mean TL 483.64 mm in R. pentasupralabialis (Table S2); 2) saddlebrown coloration of dorsal body vs. dark green or olive green coloration of dorsal body in R. pentasupralabialis; 3) the margin of the outer row forming two faint dorsolateral black cross-bars alongside body vs. absent in R. pentasupralabialis; 4) the outer margins of ventral scales and several lateral rows of dorsal scales forming ventrolateral longitudinal brownish-red coloration, with faint black spots in the middle of each ventral scale and between scales which line a black stripe vs. absent in R. pentasupralabialis (for the comparison of ventral coloration, see Figure S1).
For male specimens, the first two principal components accounted for 55.900% of cumulative coefficients. Principal component 1 (PC1) accounted for 31.464% and principal component 2 (PC2) for 24.436%. For female specimens, the first two principal components accounted for 64.567%. PC1 accounted for 39.106% and PC2 for 25.461%. Table 5 displays which characters are important in PC1 and PC2 for male and female specimens.
Figure 7 shows the plots of the first two principal components for males (A) and females (B). The PCA for male specimens did not reveal much differentiation among the localities, while the female specimens could be easily distinguished from each other (Chen et al. 2020). 
Comment 
EtymologyThe species name of the new species “chiwen” is in reference to the ninth son of Loong in ancient Chinese myth who likes eating fire, and indicates the firefly-eating habit of this new species (Yoshida et al., 2020). 
References
  • Piao Y. G., Chen Z. N., Wu Y. Q., Shi S. C., Takeuchi H., Jono T., Fukuda M., Mori A., Tang Y. Z., Chen Q., Ding L. 2020. A New Species of the Genus Rhabdophis Fitzinger, 1843 (Squamata: Colubridae) in Southwestern Sichuan, China. Asian Herpetol Res 11(2): 95–107. DOI: 10.16373/j.cnki.ahr.190068 - get paper here
 
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