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Parahelicops annamensis BOURRET, 1934

IUCN Red List - Parahelicops annamensis - Data Deficient, DD

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Higher TaxaColubridae (Natricinae), Colubroidea, Caenophidia, Alethinophidia, Serpentes, Squamata (snakes) 
Subspecies 
Common NamesAnnam Keelback 
SynonymParahelicops annamensis BOURRET 1934
Opisthotropis annamensis — SMITH 1943: 334
Parahelicops annamensis —TAYLOR & ELBEL 1958
Parahelicops annamensis — ZIEGLER et al. 2008
Parahelicops annamensis — WALLACH et al. 2014: 531 
DistributionVietnam

Type locality: Bana, Annan, Vietnam [= Ba Na Nature Reserve, Da Nang City, Vietnam], 1500 m elevation. Map legend:
TDWG region - Region according to the TDWG standard, not a precise distribution map.

NOTE: TDWG regions are generated automatically from the text in the distribution field and not in every cases it works well. We are working on it.
 
Reproduction 
TypesHolotype: MNHN 1938.0117, adult male; collected by René Bourret, 1934 
CommentP. annamensis differs from all species of Opisthotropis by its enlarged posterior maxillary teeth and its supralabials much longer than high. Its position is currently under investigation (David et al. in prep.).

Type species: Parahelicops annamensis BOURRET 1934 is the type species of the genus Parahelicops BOURRET 1934.

Diagnosis (genus). A genus of medium-sized snakes of the family Natricidae characterized by (1) body elongate, (2) head moderately distinct from the neck, (3) eye moderate in size with a round pupil, (4) maxillary teeth progressively increasing in size in a continuous series, last 2 moderately enlarged, not separated from anterior teeth by a diastema, (5) nostrils piercing distinctly dorsolaterally, (6) upper head scales complete as for typical colubroids but prefrontal single in most specimens, (7) internasals distinctly narrowed anteriorly, (8) all SL distinctly longer than high, (9) dorsal scales in 15 or 17 rows at midbody, moderately keeled at midbody, strongly keeled posteriorly, especially before vent, (10) caudal scales around the base of the tail very strongly keeled, (11) more than 110 SC, paired, (12) hemipenes short, thin, single, and spinose.
Although Parahelicops annamensis usually has a single prefrontal, as in most species of Opisthotropis, it differs from this latter genus, as defined above, by (1) maxillary teeth enlarged vs. subequal teeth in Opisthotropis, (2) tail long vs. rather short or average in Opisthotropis (see the descriptions), (3) head moderately distinct from the neck vs. barely distinct in Opisthotropis, (4) eye large vs. small in Opisthotropis, (5) nostrils directed dorsolaterally vs. directed upwards in Opisthotropis, (6) SL much longer than high vs. distinctly higher than long in Opisthotropis, and (7) dorsal pattern with two rows of large rusty blotches, vs. more or less uniform, or with crossbars in species of Opisthotropis [DAVID et al. 2015].

Diagnosis. A species of the genus Parahelicops characterized by the combination of (1) body elongate in males and females; (2) tail long with a ratio TaL / TL at least equal to 0.30, (3) maxillary teeth 28–34, the last two moderately enlarged; (4) DSR 15 or 17 at midbody, moderately keeled at midbody, strongly keeled posteriorly, usually smooth on the 1st dorsal scale row; (5) scales around the base of the tail very strongly keeled; (6) background colour chestnut brown, dark brown or dark greyish-brown; (7) dorsal pattern with isolate, bright orange or rusty-red blotches (cream or yellowish-ochre in preservative), usually horizontally elongate or vertically elongate as crossbars anteriorly, then becoming irregular, broken spots posteriorly; (8) postocular streak short, narrow, oblique, reaching the neck behind the corner of the mouth; (9) a broad, oblique and elongate orange or rusty blotch (cream or yellowish-ochre in preservative) present on the nape; (10) SL dark as the upper head surface, without defined spots or blotches, (11) venter pale in its central half with outer tips of ventral scales very dark; (12) eye moderate, 1.2–1.4 times the distance between the lower margins of eye and of lip; (13) VEN 158–172, SC 116– 146, paired; (14) internasals narrowed anteriorly; (15) SL 8 or 9; (16) prefrontal scale often single; and (17) anterior temporal single.
With its typical dorsal and ventral patterns and its long tail, Parahelicops annamensis cannot be confused with any species of the genera Opisthotropis, Paratapinophis, Amphiesma and Rhabdophis recorded from Vietnam and Laos. It is however much similar with Pararhabdophis chapaensis Bourret, 1934 (see below). It can be distinguished from this latter species by its pale venter, at least in its central area, vs. the venter entirely black in Pararhabdophis.
In collections, specimens of Parahelicops annamensis have been misidentified as Amphiesma modestum (Günther, 1875), an Indo-Himalayan species unknown east of Myanmar (our data, in prep.). Nevertheless, A. modestum has 19 DSR at midbody, 143–163 VEN, scales in the region of the base of the tail feebly keeled, and an ochre or pale brown venter [DAVID et al. 2015].

Abundance: rare. For a long time, this species has been known from only the holotype collected in central Vietnam. The second known specimen, and first recorded from Laos, was described by Stuart (2006). Subsequently, more specimens became available, especially from central Vietnam. 
References
  • Bourret, R. 1934. Notes herpétologiques sur l'Indochine Française III. Ophidiens d’Annam et du moyen Laos. Bull. Instr. Pub. Gen. Hanoi. 9 (May 1934): 167-176
  • DAVID, PATRICK; OLIVIER S. G. PAUWELS, TRUONG QUANG NGUYEN & GERNOT VOGEL 2015. On the taxonomic status of the Thai endemic freshwater snake Parahelicops boonsongi, with the erection of a new genus (Squamata: Natricidae). Zootaxa 3948 (2): 203–217 - get paper here
  • Sang, Nguyen Van; Ho Thu Cuc, Nguyen, Quang Truong 2009. Herpetofauna of Vietnam. Chimaira, Frankfurt, 768 pp.
  • Smith, M.A. 1943. The Fauna of British India, Ceylon and Burma, Including the Whole of the Indo-Chinese Sub-Region. Reptilia and Amphibia. 3 (Serpentes). Taylor and Francis, London. 583 pp.
  • Wallach, Van; Kenneth L. Williams , Jeff Boundy 2014. Snakes of the World: A Catalogue of Living and Extinct Species. Taylor and Francis, CRC Press, 1237 pp.
  • Ziegler, Thomas; Patrick David, Vu Ngoc Thanh 2008. A new natricine snake of the genus Opisthotropis from Tam Dao, Vinh Phuc Province, northern Vietnam (Squamata, Colubridae). Zoosystematics and Evolution 84 (2): 197 -203
 
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