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| Xenophidion acanthognathus Günther & Manthey, 1995
in Fukuyama, Hossman & Nishikawa, 2020.
Raffles Bulletin of Zoology. 68
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Abstract
We report a second specimen of Xenophidion acanthognathus, collected from Lambir Hills National Park, Malaysian Borneo. We investigate the taxonomic status and relationship between this species and its only other congener X. schaeferi, as possible synonymy was suggested. Morphological and genetic analysis confirmed that X. acanthognathus and X. schaeferi are heterospecific. Here, we provide a detailed morphological description and novel natural history observations of this rare species.
Key words. cyt b, Southeast Asia, Squamata, Sundaland, taxonomy, Xenophidion
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Snakes of the family Xenophidiidae consist of one genus, Xenophidion Günther & Manthey, 1995, which includes two species: X. acanthognathus Günther & Manthey, 1995, and X. schaeferi Günther & Manthey, 1995, both of which are rare and enigmatic snakes.
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Interspecific comparisons:
Xenophidion
acanthognathus can be differentiated from its sister species,
X. schaeferi by the following characteristics: larger number
of ventrals (181–185 vs. 176–178); larger number of
subcaudals (51–55 vs. 43–45); and shorter tail (SVL/tail
length = 4.20–4.52 vs. 4.69–4.84).
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| Fig. 2. The live juvenile of Xenophidion acanthognathus (SRC 00961). |
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Fig. 1. The juvenile Xenophidion acanthognathus (SRC 00961) trying to escape under the bark in situ.
Fig. 3. Ventral colouration of Xenophidion acanthognathus (SRC 00961) in life. Scale bar = 10 mm.
Fig. 4. A, right-lateral; B, dorsal; C, ventral; and D, left-lateral aspects of the head of Xenophidion acanthognathus (SRC 00961). Scale bar = 10 mm.
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Natural history. The new specimen (SRC 00961) was found
moving slowly on the trunk of a tree ca. 20 cm above the
ground in a lowland dipterocarp forest, at 2117 h (Figs. 1,
5). The air temperature at the site was 24.7°C and it had not
rained for several days except for a very light rain during the
day, thus the ground was dry. When the first author spotted
the snake under the beam of his flashlight, it tried to escape
under the bark (Fig. 1). The holotype of the species was
collected under moss covering a rock, 10 m from a stream,
at 0815 h (Günther & Manthey, 1995). One photographed
individual was found lying vertically on a damp, mossy log,
at 2015 h (Rowntree et al., 2017). The only known food
item of the species is a skink (Sphenomorphus sp.) that was
found in the gut of the holotype (Wallach & Günther, 1998).
DISCUSSION:
The results of our study demonstrate that Xenophidion
acanthognathus and X. schaeferi are sufficiently distinct
morphologically and genetically to warrant specific
status. With the acquisition of a second specimen of
X. acanthognathus, this study is the first to examine
the intraspecific variation within the species. However,
additional specimens of both species are still needed to
clarify their interspecific and intraspecific morphological
variations. Genetic material of Xenophidion from Sumatra
is also urgently needed to clarify its taxonomic status and
phylogenetic placement. The distribution of the genus that is
spread across Borneo, Peninsular Malaysia, and presumably
Sumatra reflects the connection between these land masses
until 400 kya as indicated by recent biogeographical and
geological studies (Husson et al., 2019; Sarr et al., 2019).
In addition, Xenophidion was shown to be closely related
phylogenetically to the family Bolyeridae that is found
only in the Mauritius (Lawson et al., 2004; Figueroa et al.,
2016). Only a few genera of reptiles show similar relictual
distributions in Sundaland like Xenophidion, such as the
cat gecko, Aeluroscalabotes, which is the most basal linage
and the only genus distributed in Sundaland in the family
Eublepharidae, and the false gharial, Tomistoma, which is the
sister species of Gavialis in South Asia (Willis et al., 2007;
Jonniaux & Kumazawa, 2008). Comprehensive molecular
phylogenetic analyses of these taxa may provide new insights
into the biogeographical history of Sundaic fauna.
Inger & Voris (2001) regarded X. acanthognathus as fossorial
or secretive, but Quah et al. (2018) discussed the possible
ecological niche of the genus and suggested that they may be
of semiaquatic or semi-scansorial habit, and not burrowers.
Our observation of the new specimen crawling on the trunk
of a tree may support the hypothesis of Quah et al. (2018)
that they are semi-scansorial by nature. Although many
herpetological surveys were conducted in Malay Peninsula
and Borneo, this genus has only been documented six times.
It is possible that the extremely low encounter rate in the
field with members of this genus is related to their low
density as suggested by Günther & Manthey (1995), or may
be due to specialised ecological habits. Further observations
are essential to understand the natural history of the genus.
Ibuki Fukuyama, Mohamad Yazid Hossman and Kanto Nishikawa. 2020. Second Specimen of the Rare Bornean Snake Xenophidion acanthognathus (Xenophidiidae, Serpentes, Reptilia) and Confirmation as A Distinct Species from X. schaeferi. Raffles Bulletin of Zoology. 68; 214–219.
