On the Validity of Pareas macularius Theobald, 1868 (Squamata: Pareidae) as a Species Distinct from Pareas margaritophorus (Jan in Bocourt, 1866)

2017·1.8 MB·

by  Hauser, Sjon

Tropical Natural History 17(1): 25-52, April 2017
2017 by Chulalongkorn University
On the Validity of Pareas macularius Theobald, 1868 (Squamata:
Pareidae) as a Species Distinct from Pareas margaritophorus
(Jan in Bocourt, 1866)

SJON HAUSER

71 Wiang Phing Road, Mueang, Chiang Mai 50100, THAILAND
* Corresponding Author: Sjon Hauser ([email protected])
Received: 13 June 2016; Accepted: 23 December 2016

Abstract.– The genus Pareas Wagler, 1830, consists of about fifteen species of small snail-eating snakes
distributed in China, South and Southeast Asia. Until recently, two Pareas-species ornamented with characteristic
bicolored spots were recognized, P. margaritophorus (Jan in Bocourt, 1866) and Pareas macularius Theobald,
1868. However, P. macularius was synonymized with P. margaritophorus by Huang (2004), reducing the
speciosity of the bicolored-spotted snail-eaters to a single species. This claim was tested by examining more than
60 fresh road-killed specimens of bicolored-spotted snail-eaters from northern Thailand. They were either
completely smooth-scaled, or had rows of weakly keeled dorsals. The smooth-scaled specimens differed
significantly from the keeled-scaled in a number of characters. The holotype of P. margaritophorus corresponded
closely to the smooth-scaled specimens, whereas the holotype of Pareas macularius corresponded to the keeled-
scaled ones. It was, thus, shown that P. macularius is a valid species and the synonymization as claimed by Huang
(2004) was refuted. P. macularius is distinguished from P. margaritophorus by having the 7–13 most median
rows of dorsal scales feebly keeled at midbody, by the form and color of the nuchal collar, its larger size, the
larger number of ventral shields, and the high incidence of an intense black blotch on the last, largest supralabial.
A preliminary distribution map for the two species is provided.

KEY WORDS: northern Thailand, Pareas macularius, Pareas margaritophorus, Southeast Asia, taxonomy

central mental groove separating the paired
INTRODUCTION
chin shields. Pareid snake taxonomy is an

ongoing controversy. The genus Pareas
The snail-eating snakes of South, East
differs from the other genera of the family
and Southeast Asia are presently considered
by having 15 rows of dorsal scales, the
to constitute the distinct family of Pareidae
presence of pre- and suboculars (in most
together with two other genera (Pyron et al.,
species), and characteristics of the chin
2011; Wiens et al., 2012; Reptile Database;
shields (Grossman and Tillack, 2003). It
see Savage [2015] for the correct spelling of
consists of 14 recognized species at present
the family name). Most species have a
(Reptile Database).
number of adaptations related to preying on
Three of them, Pareas carinatus Boie,
snails and slugs (Wall, 1909), such as a
1828, P. hamptoni (Boulenger, 1905), and
blunt snout, and a specialized feeding-
P. margaritophorus (Jan in Bocourt, 1866)
apparatus, including an asymmetric
are currently recognized from northern
dentition related to extracting (dextral)
Thailand (Reptile Database). Besides these,
snails from their shells (Parker and
P. macularius Theobald, 1868 had
Grandison, 1977; Hoso et al., 2007, 2010;
previously been recognized in this and
Danaisawadi et al., 2015, 2016). Another
adjacent regions as well, but Huang (2004)
morphological characteristic is the lack of a
26 TROPICAL NATURAL HISTORY 17(1), APRIL 2017
synonymized this nominal species with P. Snake’ (e.g. Cox 1991; Cox et al. 2012) or
margaritophorus. ‘Black-spotted Slug Snake’ (Nabhitabhata et
Prior to Huang’s (2004) synonymization, al. 2004); the colloquial Thai names ngu kin
P. margaritophorus and P. macularius had thak chut khao (‘White-spotted Slug-eating
been considered to occur throughout much Snake’) for P. margaritophorus and ngu kin
of mainland Southeast Asia and parts of thak chut dam (‘Black-spotted Slug-eating
southern China. Both were described as Snake’) for P. macularius (Cox 1991;
purplish-grey or brownish-grey snakes, Jintakune 2000) are translations of those
rarely exceeding 60 cm in total length. In confusing English names.
visual appearance, they are particularly The original descriptions of the two
conspicuous by having an ornamentation of nominal species in the mid-19th century
numerous black-and-white spots. These were not very clear. The description of
spots are exactly the size of a dorsal scale: Pareas macularius (Theobald, 1868) was
the anterior tip of such a scale is white, and particularly confusing because two of the
the remaining, posterior portion is black. five specimens examined by Theobald did
These bicolored spots contrast conspicuously not appear to represent bicolored-spotted
with the ground color of the skin which is slug snakes at all (Sclater, 1891; Das et al.,
greyish (densely speckled with fine dark 1998). However, in the classic work of
grains). Some bicolored spots appear to be Boulenger (1896), P. margaritophorus and
completely black, since the tiny white P. macularius emerged as two clearly
anterior tip of each scale is completely distinct species. In the meantime, three
covered by the posterior black portion of the rather similar species of snail-eaters were
preceding scale. These bicolored spots are described and considered valid in
not randomly distributed, but usually form a Boulenger’s work. Another bicolored
number of rather narrow, transverse series. spotted snail-eater was also added to the list
Even when both P. margaritophorus and P. published in 1935 by R. Bourret.
macularius were considered as valid, they The situation was completely reversed
could not be distinguished by the shape or when Smith (1943) synonymized one of
distribution of these spots. Superficially, these newer species with P. margaritophorus,
therefore, the two nominal species showed and three others with P. macularius. Of the
considerable morphological similarity by previous six species of ‘spotted snail-
the presence of at least a good number of eaters’, only two remained. The final blow
conspicuous bicolored spots. to the speciosity of the spotted snail-eaters
These spots have given rise to the came sixty years later when Huang (2004)
scientific names of both Pareas synonymized P. macularius with P.
margaritophorus (the specific nomen margaritophorus, resulting in only one valid
meaning ‘pearl carrier’) and Pareas species. This complex history is
macularius (the specific nomen meaning summarized in Fig. 1.
‘spotted’). Confusing colloquial English and Huang’s synonymization coincided with
Thai names also referred to these spots: In another publication, in which the authors
English, P. margaritophorus was known as also ‘believe that Pareas macularius
‘White-spotted Slug Snake’ (e.g. Cox et Theobald, 1868, is a synonym of P.
al.1998, Nabhitabhata et al. 2004), whereas margaritophorus (Jan, 1866)’ (Guo and
P. macularius was known as ‘Spotted Slug Zhao, 2004). Authors of these works seem
HAUSER — ON THE VALIDITY OF PAREAS MACULARIUS 27

FIGURE 1. History of descriptions of new species of ‘spotted snail-eaters’ and their subsequent
synonymizations.
to have paid little attention, if any, to Smith [southeastern Myanmar], respectively).
(1943), and most of other subsequent works, Nevertheless, Huang’s (2004) account was
including Taylor (1965), in which P. adopted in most subsequent Chinese studies,
margaritophorus and P. macularius were such as Guo and Deng (2009) and Guo et al.
apparently well-defined against each other. (2011), although a few others continued to
In Chan-ard et al. (1999), six pictures of recognize P. macularius as valid (e.g., Yang
spotted snail-eating snakes were published, and Rao, 2008). In the meantime, Vogel
each of which was identified correctly as (2009) expressed his conservative stance
either P. margaritophorus or P. macularius. against Huang’s (2004) claim due to the
In this period, the validity of each of the two absence of examination of type materials
species was not questioned by any therein. Notwithstanding these views, the
taxonomists. Living specimens that before synonymization has been gradually and
Huang’s (2004) synonymization would have broadly approved by authors in subsequent
been identified as P. margaritophorus, and publications, leading to the removal of P.
P. macularius, are shown in Fig. 2, macularius from most recent lists of
respectively Fig. 3. recognized Pareas species, including that in
Huang’s synonymization was made the reputed Reptile Database (see above). In
solely on the basis of information from a number of collections, specimens initially
Smith’s (1943) description and data from identified as P. macularius were renamed P.
Chinese specimens, i.e., without examining margaritophorus. In at least one study, such
holotypes of P. margaritophorus and P. renamed specimens were subjected to DNA
macularius, despite their non-Chinese extraction and analysis, resulting in the
origins (“Siam” [Thailand] and Martaban conclusion that ‘Pareas margaritophorus’
28 TROPICAL NATURAL HISTORY 17(1), APRIL 2017
showed remarkably large sequence often fails to result in evertion of
divergences (Guo et al., 2011). hemipenes. However, the sex of many
In the present paper, I resurrect P. specimens could be determined with high
macularius as a valid species based on the probability by the relative tail length.
analysis of morphological data of many Subsequently, a note was made on the
road-killed specimens found in northern habitat of the collecting site, which was
Thailand. specified as the distance (by road) in
kilometers to the nearest large village or
district town (e.g. Highway 1095, 5 km
MATERIALS AND METHODS
northwest of Mae Sae, Mae Taeng District,

Chiang Mai Province). The elevation of the
Sixty-one relatively intact, freshly road-
collecting sites could later be estimated with
killed (DOR) specimens, showing
the help of maps (1:50,000) from the Krom
characteristics of P. margaritophorus sensu
Phaen Thi Thahan of the Kong Bancha Kan
Huang (2004), were collected during the
Thahan Sung Sut (“Thai Army Maps”) on
rainy seasons of 2011-2015. They all
which 25-meter jumps in elevation are
originated from northern Thailand (the
visualized by a dense network of lines. The
provinces of Chiang Mai, Chiang Rai,
less detailed 1:250,000 Thai Army Maps of
Lampang, Lamphun, Mae Hong Son, Nan,
the same publisher have been useful for
and Phayao), including the ‘lower north’
provinces of which no 1:50,000 maps were
(the provinces of Phetchabun, Phitsanulok,
available. It was later shown that elevations
and Tak), a region close to the localities
estimated using these methods were
from which the holotypes of P.
usually within the range of measurements
margaritophorus and P. macularius had
with GPS ± 100 meter.
originated.
The specimens were temporarily stored
Each specimen was photographed on
in 70% ethanol and, after several days, were
detection at the collecting site, and the
transferred to 8-10% formalin. After
presence or absence of keeled dorsal-scale
fixation in formalin for a varying period, all
rows was determined by carefully screening
were transferred again to 70 % ethanol.
the dorsal surface with a magnifying glass.
The following characters could be rated
The total length (TL) and tail length (TaL,
in nearly all specimens:
from the tail tip to the posterior edge of the
• The number of ventral shields (V):
anal shield) of most fresh specimens were
Counted following Dowling (1951).
measured (in mm), and the relative tail
This corresponds closely to the scale
lengths, TaL/TL (in %), were calculated for
count starting from the second scale
comparisons. Specimens with aborted eggs
of the throat twice as wide as long
beside them were considered females, while
until and including the ventral shield
specimens with one or both hemipenes
just before the anal shield. The first
everted from the vent were scored as males.
scale of the throat also twice as wide
For the remaining specimens (the majority),
as long, was considered a preventral
the tail was squeezed and massaged from its
shield and, thus, was excluded from
center towards the vent, which resulted in
the count together with the anal
everting hemipenes in a good number of
shield.
them. In damaged specimens, this procedure
HAUSER — ON THE VALIDITY OF PAREAS MACULARIUS 29
• The number of subcaudal pairs (SC): This blotch could be easily
Counted with an exclusion of the distinguished, when present, in most
terminal scute. specimens including those with
• Special attention was given to the seriously damaged heads. Greyish,
form and color of the nuchal collar in diffuse, or speckled blotches on this
the fresh material, as two different shield were rated as absence of
collar types could be distinguished, a blotch.
sulphur (pale yellow), pink or reddish The dorsal scale row formula examined
collar without speckling (Type I) and in a large number of specimens (and as
an often characteristic W-shaped given in literature) was always 15:15:15 and
collar with fine brown speckling was, therefore, discarded for the analyses.
(Type II). As anal shields were consistently entirely,
For determining the type of collar, color this character was also ignored.
pictures of fresh specimens were essential, All specimens had numerous bicolored
because the coloration of the Type I-collar spots and their presence was not listed. The
rapidly faded during preservation in alcohol size of the vertebrals relative to adjacent
or formalin. scales (enlarged versus normal) was also
• The amount and pattern of spots, excluded from the analyses, because the
speckles and blotches on ventral state of this character was extremely
scales were rated by the author from 1 difficult to quantify exactly. Likewise, it
to 5: 1 = sparsely speckled, anteriorly was nearly impossible to quantify the body
almost completely white with small shape (round versus laterally compressed) in
spots restricted to the lateral edges of the DOR-material. Thus, variation in this
the ventral scales; 3 = moderately character was also ignored.
speckled, more and larger speckles Dentition and hemipenal structure were
than in 1, posteriorly some blotches not examined for practical reasons.
as wide as half the width of the Examination of the former in such small
ventral scale; 5 = densely speckled, animals as snail-eaters would be technically
speckles and blotches dominating, difficult and required too much time.
posteriorly with numerous large Moreover, the dentition was apparently
blotches often shaped like the blades severely damaged in many road-killed
of knives. All other ratings are specimens. In the majority of specimens in
estimates in between these three which the base of the tail was damaged,
values. hemipenes could only be partly everted, or
• No attention was paid to the head not at all. In just a few specimens, the
scalation as head shields were badly hemipenes could be everted completely and
damaged in most specimens, making were photographed. In specimens preserved
it impossible to observe or precisely in alcohol or formalin, this tiny, hollow
count infra- and supralabials, oculars, structure was usually shrunk.
and temporals. Even so, the presence All 61 preserved specimens used in this
or absence of a large, conspicuous study were deposited in the collection of the
solid, intensely black blotch (IBB) Queen Saovabha Memorial Institute (QSMI)
that covers much (30-60%) of the last in Bangkok, Thailand.
(usually 7th) supralabial was recorded
30 TROPICAL NATURAL HISTORY 17(1), APRIL 2017

FIGURE 2. A living specimen of the smooth-scaled type of the spotted snail-eater (SHPC12.12.12-01) from
lowland in Mueang District, Chiang Mai Province, Northern Thailand.
Supportive specimens LSUHC-La Sierra University
A large number of photographs of Herpetological Collection, La Sierra,
spotted Pareas-specimens in museum and California, USA; LSUDPC-La Sierra
private collections, as well as those in University Digital Photo Collection, La
herpetological publications, were examined. Sierra, California, USA; MNHN-Muséum
The holotypes of Leptognathus margaritophorus National d’Histoire Naturelle, Paris, France;
(Jan in Bocourt, 1866) and Pareas NHW-Naturhistorisches Museum Wien,
macularius Theobald, 1868 were Vienna, Austria; QSMI-Queen Saovabha
particularly important to this study. The Memorial Institute, The Thai Red Cross
relevant data of these specimens were Society, Bangkok, Thailand; SHPC-Sjon
extracted from photographs and literature Hauser’s Private Collection, Chiang Mai,
(e.g., Boulenger, 1896). Thailand; SKKCC-Stan Klaassens’ Ko
Abbreviations of museums and other Chang Collection, Ko Chang, Trat,
collections Thailand; SMF-Senckenberg Museum
BM(NH)-British Museum (of Natural Frankfurt, Frankfurt am Main, Germany;
History), London, UK; CAS-California THNHM-Thai Natural History Museum,
Academy of Sciences, San Francisco, Nakhon Pathom, Thailand; ZFMK-
California, USA; CIB-Chinese Institute of Zoologisches Forschungsinstitut und
Biology, Chengdu, China; EHT-HMS-E.H. Museum Alexander König, Bonn, Germany;
Taylor, private collection; FMNH-Field ZRC-Zoological Reference of the Raffles
Museum of Natural History, Chicago, USA; Museum of Biodiversity at the National
HNU-Hainan Normal University, Hainan, University of Singapore, Singapore.
China; IEBR-Institute of Ecology and
Biological Resources, Hanoi, Vietnam;
HAUSER — ON THE VALIDITY OF PAREAS MACULARIUS 31

FIGURE 3. An adult specimen of the keeled-scaled type of the spotted snail-eater from evergreen forest in
Kaeng Krachan National Park, Phetchaburi Province, western Central Thailand. Photograph: Ton Smits.
differential male/female ratio between the
RESULTS
two groups, because, although females

tended to have larger bodies with more
Fresh material from northern Thailand
ventrals in either group of specimens, the
Of more than 120 fresh DOR-specimens
keeled specimens contained a slightly lower
collected and briefly examined, the 61 most
proportion of females (58%) than the
intact specimens were preserved and used
smooth-scaled specimens (60%). The males
for this study. Of these, 37 had completely
of the keeled-scaled specimens were larger
smooth dorsal scales, while the remaining
and had more ventrals than the smooth-
24 had keeled dorsal scales in 7-11 of the
scaled males, whereas the keeled-scaled
invariably 15 rows. The presence or absence
females were also larger with more ventrals
of keels strongly correlated with other
than the smooth-scaled females (Table 1).
characters (Table 1).
As a whole, the keeled-scaled snakes also
Body size and scale counts
had relatively longer tails than the smooth-
Specimens with the presence of keeled
scaled snakes, and this is also true when the
dorsal scales were larger in TL than those
male and female specimens were separately
with only smooth dorsal scales. Also, the
compared between the two types.
former had higher numbers of ventral
For the relative tail length, there was no
shields than the latter (Table 1). These
significant difference between the smooth-
differences are graphically illustrated in
scaled and the keeled-scaled specimens,
histograms (Figs. 4, 5).
when both sexes were combined for
The larger body size of the keeled-scaled
comparison. However, smooth-scaled males
specimens and their higher number of
had longer relative tail lengths than the
ventral scales are not attributable to
keeled-scaled males, whereas the smooth-
32 TROPICAL NATURAL HISTORY 17(1), APRIL 2017
TABLE 1. A summary of selected data from 37 smooth-scaled and 24 keeled-scaled specimens of bicolored-
spotted snail-eaters.

average TL in average TaL in average
sex ratio mm and mm and TaL/TL (%)
(% males) STDEV STDEV and STDEV
smooth-scaled males 100% 335.4 ± 38.2 69.8 ± 9.0 20.8 ± 0.9
keeled-scaled males
100% 448.3 ± 41.7 86.6 ± 12.7 19.25 ± 1.36
t-test (2,3) p<0.001 p<0.005 p<0.01

smooth-scaled females
0% 363.0 ± 42.4 52.6 ± 5.4 14.5 ± 0.72
smooth-scaled males
0% 423.1 ± 63.9 64.4 ± 10.4 15.2 ± 0.74
t-test (2,3)
p<0.01 p<0.005 p<0.05

smooth-scaled
(males+females+sex unknown)
40% 353.7 ± 42.3 59.9 ± 10.9 17.1 ± 3.1
keeled-scaled
(males+females+sex unknown)
42% 433.6 ± 119.0 68.3 ± 15.8 16.9 ± 2.3
t-test (2,3)
p<0.001 p<0.001 n.s.

scaled females had shorter relative tail conspicuous, but sometimes reduced to a
lengths than the keeled-scaled females. small dot or even to a narrow stripe. In this
There was no significant difference in the type the collar was almost always white,
number of subcaudal pairs between the cream, yellowish, pink or reddish/orange
smooth-scaled and keeled-scaled specimens, without fine speckles: however, there
when males and females were combined for sometimes were a few black spots.
comparison. This was also true when the A Type II-collar was usually shaped like
smooth-scaled males were compared with a gothic letter W, or butterfly-shaped, often
the keeled-scaled males. However, the with two black round blotches enclosed. Its
keeled-scaled females had higher numbers shape could also be amoeboid.
of subcaudal pairs than the smooth-scaled Occasionally, these collars had two “tails”
females. stretching posteriorly. The Type II-collar
Shape, color, and extent of speckling of was speckled with fine brown pigment; the
the collar speckling might be very dense, so that the
Based on the shape, color, and extent of collar was hardly distinct from the
speckling of the collars, the specimens could surroundings. The appearance was whitish
be divided into two types. when the fine brown speckling was very
A Type I-collar was an entire band or a sparse (or sometimes even absent), and,
band partially or completely broken into more often, light brown when the speckling
three dots (tripartite or triple dot), of which was moderate, or dark brown when it was
the two lateral dots were often dense. Various forms of both collar-types
inconspicuous: the central dot was usually are illustrated in Figs. 6, 7 and 8.
HAUSER — ON THE VALIDITY OF PAREAS MACULARIUS 33
TABLE 1. continued.

average average number average belly
number V and SC-pairs and incidence speckling and
STDEV STDEV collar type of IBBs STDEV
141.2 ± 4.6 49.2 ± 1.9 100% I 4.20% 1.61 ± 0.68
157.1 ± 3.2 4 8.7 ± 3.1 100% II 100% 4.3 ± 0.71
p<0.001 n.s. p<0.001

150.2 ± 3.7 39.0 ± 2.3 100% I 0% 1.88 ± 0.90
157.0 ± 4.9 43.0 ± 2.1 85.7% II 95.80% 3.68 ± 0.80
p<0.001 p<0.001 p<0.001

146.6 ± 6.0 43.0 ± 5.4 97% I 0% II 3% 1.71 ± 0.88
157 ± 4.2 45.4 ± 3.8 0% I 94% II 98% 3.9 ± 0.81
p<0.001 n.s. p<0.001

Nearly all of the smooth-scaled Hemipenal structure
specimens (97%) had a Type I-nuchal In only a few specimens, for each of the
collar, but this type was not found in the smooth-scaled and the keeled-scaled types,
keeled-scaled specimens. On the other hand, hemipenes could be everted completely. The
nearly all of the keeled-scaled specimens pictures of these hemipenes showed that
(94%) had a Type II-nuchal collar, whereas they were deeply forked with numerous
such a collar was absent in the smooth- folds and papillae, and no spines. In the
scaled specimens. In a few specimens (3% present observations, however, detailed
of the smooth-scaled and 6% of the keeled- morphology and arrangement of these folds
scaled), no collar could be distinguished. or the shape and distribution of papillae
Intensive black blotches and belly speckling remained obscure. I, thus, refrained from
In the keeled-scaled specimens, there attempting to quantify possible differences
was a very high incidence of an IBB on the in these characters between the smooth-
posterior part of the spoon-shaped, last scaled and keeled-scaled specimens.
supralabial (98%), whereas it was very low
Conclusion
(3%) in the smooth-scaled specimens.
From the analyses of the data as
The speckling and mottling of the belly
summarized in Table 1, it is obvious that the
appeared to be much denser in the keeled-
keeled-scaled and smooth-scaled populations
scaled specimens. For objective comparison,
represent two distinct species, each with a
however, this character further needs an
set of explicit diagnostic characters.
appropriate quantification procedure. Examples
Additional, indirect support for their
of sparse and dense belly speckling are
distinctiveness comes from the localities
illustrated in Fig. 9 and Fig. 10.
34 TROPICAL NATURAL HISTORY 17(1), APRIL 2017

FIGURE 4. The total lengths in mm of the smooth-scaled specimens (blue) compared to those of the keeled-
scaled ones (red).
where the specimens were collected: All The holotype of Leptognathus
smooth-scaled specimens were found at margaritophorus Jan in Bocourt, 1866
elevations below 800 m (150-800 m) a.s.l., The holotype of Leptognathus
while all keeled-scaled specimens were margaritophorus Jan in Bocourt, 1866,
collected at elevations above 800 m a.s.l. deposited in the Muséum Naturelle
(Fig. 11). These data show that the two d’Histoire Naturelle in Paris, France, as
species are sympatric in much of northern MNHH 599, is labeled as having originated
Thailand, but they are rarely syntopic. from “Siam” (=Thailand). Careful

FIGURE 5. The numbers of ventral shields of the smooth-scaled specimens (blue) compared to those of the
keeled-scaled ones (red).