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Isanophis boonsongi new comb., preserved
holotype (FMNH 135328). From
top to
bottom: Dorsal view - Ventral view -
Lateral view of the head and neck,
left side.
Photographs by Patrick David.
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There is little doubt that Southeast Asia harbors the most diverse assemblage of living snake species. And, a number of species from the Indochinese region, including Thailand, are still poorly known only, in some cases known only from their holotype or type series, or at best a handful of specimens. Natricid snakes are particularly diverse in Southeast Asia and three genera contain species that seem to be restricted to very small ranges, they are all aquatic and despite being described in the mid-20th century have remained enigmatic.
Angel’s stream snake, Paratapinophis
praemaxillaris described by Angel in 1929, has been known from two syntypes
from northern Laos, and six other specimens from China and Thailand. Two other
natricine species, Pararhabdophis
chapaensis and Parahelicops
annamensis both described by Bourret in 1934, were previously known from
their respective holotypes. However, Stuart (2006) described a second specimen
of P. annamensis, from Laos in 2006. Recently,
intensive fieldwork in northern Vietnam and Laos, recovered about 10 specimens
of Parahelicops annamensis and Pararhabdophis chapaensis each. Another
rare species, Parahelicops boonsongi described
by Taylor and Elbel in 1958 was described on the basis of a single specimen
from Loei Province in northeastern Thailand. Subsequently, two additional
specimens, also from Loei Province were found by Cox in 1995.
Taylor and Elbel placed their new species to the genus Parahelicops because of morphological
similarities with P. annamensis, such
as the single prefrontal. However, the generic status of Parahelicops has been controversial since its description. It was
established by Bourret for a new species, Parahelicops
annamensis, on the basis of a single specimen with the following
characters: 25 subequal maxillary teeth, the last two enlarged; head quite
distinct from the neck; eye small with a round pupil; nostrils directed
upwards; two internasals, a single prefrontal; elongated body, slightly
laterally compressed; dorsal scales keeled, without apical pits, in 15 rows;
tail long; subcaudals paired; hypapophyses developed throughout the vertebral
column. Bourret (1934b) also noted its similarity to Opisthotropis but differed in dentition, having its head distinct
from the neck, and its elongated body.
Parahelicops boonsongi
was described by Taylor and Elbel in 1958 and is known from only three
specimens from Thailand. It has been placed either in the genus Parahelicops Bourret, 1934, along with Parahelicops annamensis, as well as the
genus Opisthotropis Günther, 1872. In
a new paper David et al. (2015) compared its morphological characters with
those of P. annamensis and with three
other relevant genera, Opisthotropis,
Pararhabdophis Bourret, 1934, and Paratapinophis Angel, 1929. Parahelicops boonsongi is phenotypically
distinct from Parahelicops annamensis,
Opisthotropis, and all other
natricine genera. The authors erect a new genus, Isanophis gen. nov., to accommodate Parahelicops boonsongi. How these snakes are related to each other
and other natricids remains to be determined.
Citation
David, P., Pauwels, O. S., Nguyen, T. Q., & Vogel, G.
(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.