Hypsirhina innominata Morice, 1875c Coup
d'Oeil sur la Fauna de la Cochinchine Francaise, 1875c:58. Type locality:
from Tay-ninh, Cochin China (South Vietnam, on the Cambodian border). Holotype:
MHNL 42000338.
Hypsirhina
jagorii – Tirant, 1885 Notes sur les
Reptiles…. De la Cochinchine et du Cambodge, p. 44.
Enhydris innominata - Smith 1929 Journal
of the Natural History Society of Siam 8:49.
Enhydris
innominata innominata Saint Girons 1971 Société
du Science Naturelles Physiques du Maroc 51:221.
Comment
Saint Girons (1971) relegated Hypsirhina longicauda Bourret and H. smithii Boulenger to races of E. innominata. Note that elsewhere in this work E. smithii was placed in the synonymy of
E. jagorii. There is little doubt
that longicauda, jagorii, and innominata are closely related and that
their relationships might be better expressed as races of jagorii (the oldest name of the three). Morphologically these
snakes are very similar and differ from each other primarily in ventral and
subcaudal counts, color patterns, degree of tail compression, and sexual
dimorphism.
Etymology: The name innominata
is derived from the Latin innominatus,
meaning “nameless”.
Common Name: Mekong Delta Watersnake (Stuart, 2004).
Distribution: This species is endemic to the lower Mekong drainage basin in southern Vietnam and it probably extends up the Mekong Valley to Cambodia. Tirant (1885) reported
E. jagorii from “Cholon,” Cambodia with 106 ventral scales. This record is most likely based on this species, the only known
Enhydris with an extremely low ventral count. Tirant’s locality is undoubtedly the same as Cholng, Cambodia on the Mekong (12o15’N, 105o58’E), it is about 100 km north of the Tay Ninh type locality for
E. innominata. Smith (1929) rediscovered Morice's type specimen of
E.
innominata which had been labeled "
Hypsirhina plumbea varieté 1874" in the Museum at Lyon, France. Campden-Main (1970) listed only the type locality (Tay Ninh) as the distribution, and based his account on Malcolm Smith’s 1943 work. Gyi (1970) stated that this snake occurs in Cochin China (= Vietnam) and Thailand but cited no specimens from Thailand. It seems likely that he confused it with
Enhydris jagorii (then considered to be
E. smithii). Recent collections made by Bryan Stuart extend its range southward into the Mekong delta.
Diagnosis: Enhydris innominata
has 21 scale rows at midbody, an extremely low ventral count (106 -117), and a
highly distinctive pattern of black lateral blotches that are scalloped-shaped
that arise from the ventral surface. It
can be readily separated from E. enhydris
and E. subtaeniata, both of which
have smooth, striated dorsal scales and elongated anterior chin shields. Both
of these species also have 137 ventral scales or more. Table 11 compares it to
other species within the Enhydris jagorii
Group, and it is most readily confused with these close relatives which have
smooth, non-striated dorsal scales and flared anterior chin shields. Enyhdris innominata has 23 - 25 scale
rows on its neck, while E. chanardi
has 20 - 23 (usually 21) scale rows on the neck. Additionally, E. chanardi
has a higher ventral scale count (110 - 125), small dorsolateral spots that
involve two or three scales; and larger, plate like temporal scales. Enhydris jagorii also has a higher
ventral count (117 - 127), the same number of scale rows on the neck (23 - 25),
small temporal scales, but a pattern similar to innominata. Enhydris longicauda has more ventral
scales (122 - 136) and more subcaudal scales (52 - 76) than innominata which has 42 - 56 subcaudal scales.
Size: The largest female measured for this study had a total
length of 655 mm, with a 50 mm tail. The largest male measured was 390 mm SVL
and a damaged tail. Tails of males were 25 - 33% of the SVL; females had tails
that were 18 - 24% of the SVL. The smallest measured was a male with a total
length of 233 mm and a 47 mm tail. The smallest female measured was one of the
syntypes that had a total length of 215 mm with a 39 mm tail.
External
Morphology
The
head is narrow and moderate in length. The eyes are dorsolateral, and their
diameter is about half of the eye-nostril distance. The interocular distance is
greater than the length of the frontal.
On
the head the rostral scale is pentagonal and at least twice as broad as tall. It is slightly visible from above. The nasals are
semi-divided and the nasal cleft touches the first labial.
The internasal is single and broad, posterior to the nasals, and penetrates the
nasals slightly, and it is in narrow contact with the loreals. The two prefrontals contact the loreal, the supraocular, and the preocular
scales. The frontal is almost as long as the interorbital
distance, and the parietals are slightly longer than the frontal. The
supraocular scales are rectangular, usually single but may be divided; the
preocular is usually single but may be divided, it is narrow and tall, its
ventral edge is wider than the dorsal edge; and the upper postocular scale is
tall and narrower than the bottom postocular scale. The single loreal contacts
upper labials 1 - 3. The temporal formula is 1 + 2 + 3. The third row of
temporal scales has an enlarged upper scale but the bottom two scales are
indistinguishable from dorsal scales. The upper labials usually number eight,
but may be seven or nine. The fourth upper labial enters the orbit. Four of 18 specimens examined had the rear
upper labial divided on one side.
On
the chin the lower labials number 9 - 12, 11 is the usual number; the largest
can be the fourth or the sixth. Lower labials 1 - 4, 1 - 5, or 1 - 6 contact
the anterior chin shields. The anterior chin shields are longer than the posterior
pair and bordered by lower labials 1 - 4, 1 - 5, or 1 - 6. The posterior pair
is separated by a pair of smaller scales. The gulars number 6 - 9.
On
the body the anterior dorsal scale rows on the neck number 21 - 25; at mid-body
number they number 20 - 23, with 21 the usual number. The syntype MHNL 42000338
has 23 rows at mid-body; Smith (1943) also noted this unusual scale count for
this species. Scale rows in front of the vent are reduced to 19 or remain at 21
rows. Scales in the first row are larger than those of the second row. The
dorsal scales become more ovate posteriorly and do not have ornaments. The
ventral scale count range is 108 - 117; 108 - 117 in males and 111 - 116 in
females. The ventral scales are wide, about 3 - 4 times the length of a near by
dorsal scale, and are rounded. The anal plate is divided and about 1.5 times
the length of a ventral.
On
the tail the dorsal scale rows at the base of the tail number 11 and are ovate.
The subcaudal scales for 18 specimens are divided and number 42 - 56, nine males
have 51 - 56, and nine females have 42 - 49. Thus, this species shows sexual
dimorphism in the number of subcaudal scales, as does the tail/SVL ratio. The
tail is slightly compressed at the base, and becomes more strongly compressed
near the distal end. At the base the width is 78% of the height based upon the
average of three specimens.
Color
and Pattern. Head brown with some mottling. A posterior eye stripe(s) evident
in most of the specimens examined. Vertebral row of spots with paravertebral
scales involved. A second row of spots occurs on each side on dorsal scale rows
eight and nine. Lateral black blotches three scale rows wide are separated by
white or yellow bars that are less than one scale wide. This alternating
lateral pattern is on scale rows 1 - 6 or 1 - 8. The ventral scales and chin
are yellow with some intrusion of black pigment. Two juveniles (BM 1938.1.1.3.1
and LSUMZ 29599) show three rows of dorsal spots; and dark lateral blotches are
separated by yellow cross bars about one scale wide. The dark blotches and
yellow bars number 32 - 44 each on the body. They continue on to the tail (and
number about 22). The dark blotches are on scale rows 1 - 8 or 1 - 6 and some
of the dark pigment extends onto the venter. The amount of yellow pigment on
the venter is variable. The top of the head has dark spots on an almost black
ground color. In adults the three rows of spots found in juveniles become fused
into a series of single blotches.
Habitat: Enhydris innominata uses artificial canals, flooded grasslands, and Melaleuca swamp forest (Bryan Stuart,
personal communication). This habitat is within the Tonlé Sap-Mekong Peat Swamp
Forest ecoregion of Wikramanayake et al. (2002).
Reproduction: Three
gravid females were examined (FMNH 259249, 259252-3) they were 465, 501, and
555 mm SVL and contained 13, 32, and 32 eggs respectively (= 25.6). Embryos were not
detected in any of the eggs and they were collected in South Vietnam in late
October and November.