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Amphiesma stolatum from Thailand. JCM |
Asia
is the geographic center for the origin of most modern snake lineages. The
Asian natricines known as keelbacks (Amphiesma)
are widely distributed and inhabit a variety of niches and exhibit significant
morphological variation. The genus keelbacks in the genus Amphiesma comprise at least 42 species of small to medium-sized (not
exceeding one meter) of snakes. They are terrestrial to semiaquatic, oviparous,
and generally considered harmless or mildly venomous.
Species in this group range
throughout southern, eastern, and southeastern Asia, from Pakistan and India to
eastern China, north into southernmost Russia and Japan, and southwards to
Sumatra. In the mid-20th century Edmund Malnate used morphological
characters including hemipenial morphology, dentition, and external scalation
to divided the genus Natrix sensu
lato into several genera, revalidating the genus Amphiesma Duméril, Bibron, and Duméril with the type species Amphiesma stolatum. The diagnostic
characters of Amphiesma are defined
as: hemipenes and sulci spermaticus simple; maxillary teeth in continuous
series, gradually becoming larger posteriorly in the series or the last two
teeth abruptly enlarged; terrestrial; internasals broad anteriorly, nostrils
lateral; apical pits present or absent. Recent molecular phylogenies suggest
that this genus is not monophyletic, and that additional cryptic diversity is present.
All analyses consistently show Amphiesma
consists of three distinct, monophyletic lineages.
In a
recently published paper Guo et al (2014) divide Amphiesma into three genera, Amphiesma, Hebius, and Herpetoreas.
The genus Amphiesma is monotypic, Herpetoreas contains three species, and Hebius comprises the remaining 39
species. On the basis of a combination of molecular analyses and external
morphological comparisons, they describe a new species in the Herpetoreas group from China as H. burbrinki sp. nov. Several other
species are shown to be non-monophyletic or contain significant levels of
intraspecific genetic diversity. They also found another Old World natricine
genus, Xenochrophis non-monophyletic
and suggest further taxonomic revisions are needed in the Natricinae, at
multiple levels.
Citation
Guo P, Liu Q, Zhang L, Ll J X,
Huang Y, Pyron RA. 2014. A taxonomic revision of the Asian keelback snakes,
genus Amphiesma (Serpentes:
Colubridae: Natricinae), with description of a new species. Zootaxa,3873:
425-440.