Sumatran Mud Snake, Sumatranus albomaculatus (Duméril, Bibron, and Duméril 1854)
Homalopsis albomaculatus Duméril, Bibron, and Duméril, 1854 Érpétologie générale...reptiles. Paris 7(2):974. Type locality: Padang, Sumatra. Holotype: MNHN c3452.
Hypsirhina albomaculata - Jan, 1863, Elanco systematico degli ofidi, p. 77.
Enhydris albomaculata - Haas, 1950 Treubia, 20(3):575.
Sumatranus albomaculatus Murphy and Voris, 2014:37.
Etymology. The name albomaculata presumably refers to the white spots on the head and dorsum, and is derived from the Latin albus meaning “white” and macula meaning “spot”.
Distribution. Sumatranus albomaculatus is a Sunda Shelf endemic. This species lives on the following islands that are near Sumatra: Nias, Pulo, Simeuluë, Sibigo, and Sinabang. Its presence on Sumatra proper is questionable. Gyi (1970) may have been confused when he listed Java within the range of this species; the place names he listed are small islands around Sumatra and none of these names are associated with Java. In fact, other than the type locality all of the localities appear to be offshore satellites of Sumatra. This snake’s presence on numerous small islands suggests it may have a tolerance for saltwater, or if it is freshwater it may have been isolated on these islands for long periods. The web site for the Pula Simeulue Wildlife Reserve lists albomaculatus as present. Simeulue is surrounded by deep water and is about 100 km NW of Sumatra. This population has probably been isolated from other populations for a while. Sumatranus albomaculatus inhabits the Sunda Shelf and Philippine Bioregion of Wikramanayake et al. (2002).
Diagnosis. A homalopsid that has 27 scale rows at mid-body (26 - 28), at least one literature report described three specimens with 25 scale rows (I have not examined any specimens with 25 scale rows). Four upper labials contact the loreal. These labials (except the first) have a broad dorsal edge. The upper labials posterior to the eye may be divided, particularly the last large labial. The first five or six lower labials contact the anterior chin shield. This species may be most easily confused with Phytolophis punctata, which has 25 or 27 scale rows at mid-body, a mostly black dorsum, and with which it may have an over-lapping geographical distribution. However, P. punctata has horizontally divided labials under the eye, a small (usually single) internasal that is isolated from the loreal. S. albomaculatus has a large internasal scale that contacts the loreal. P. punctata also has four labials contacting the loreal but these taper toward the dorsal edge. Subsessor bocourti has 27 or 29 scale rows at mid-body; it usually has a single internasal, and has upper labials 1 - 2 or 1 - 3 in contact with the loreal. It also has horizontally divided upper labials behind the eye. Dieurostus dussumieri also has 27 scale rows at mid-body but it can be distinguished from albomaculatus by a divided internasal which does not contact the loreal in the one specimen examined, and upper labials 1 - 3 contacting the loreal (albomaculatus usually does not have the first labial contacting the loreal). Additionally, D. dussumieri is known only from southwestern peninsular India. See Table 5 for a comparison of species with 27 scale rows at mid-body.
Size. The largest individual measured was a female with a total length of 625 mm and 75 mm tail. The largest male measured had a total length of 520 mm with a 90 mm tail. The smallest individual measured had a 260 mm SVL with a 70 mm tail. Gyi (1970) noted that females have significantly shorter tails than males. Data collected for this study show females have tails that are 12.5 - 14.4% of the SVL, while males have tails that are 17.1 - 26.9% of the SVL.
External Morphology. The head is distinct from the neck and slightly depressed. The eyes are dorsolateral and are small; their diameter is about equal to the width of the prefrontal scales, or about 1.5 times the eye-nostril distance.
On the head the rostral is pentagonal and two or three times broader than tall, it is slightly visible from above. The nasals are semi-divided with the cleft touching the loreal or the second labial, or divided with the cleft touching the labial or loreal and the internasal. The internasal scale is divided and slightly penetrates the nasals from behind. They are small, each covers about half the area of the nasal, and they are in contact with each other. The prefrontal scales are about twice the size of the internasals in area, they are paired and in contact. Rooj (1917) reported that none of 10 specimens from Simalur have divided prefrontals. The frontal is pentagonal to hexagonal and relatively short, about 1.25 times the length of the supraocular. The parietals are large and entire, almost twice the area of the frontal. The supraocular is single and the anterior margin is only slightly narrower than the posterior margin. The loreal is single and in contact with upper labials 2 - 4 and occasionally 1 - 4. The single preocular is taller than wide. The postocular can be single or paired, it paired the two scales are about equal in size. The temporal formula is 1 + 2 + 3 or 1 + 2 + 4; the third row is indistinguishable from the occipital scales. The upper labials number eight, occasionally nine; labials posterior to the eye may be divided horizontally. The fourth and or fifth upper labials enter the orbit, the dorsal edge of these scales have been squared off.
On the chin lower labials number 11 - 14, with number seven or eight being the largest. They are extremely tuberculate. The first on each side form the mental groove. The first five or six are in contact with the anterior pair of chin shields. The anterior pair of chin shields is 3-4 times larger than the second pair. The second pair is separated by a smaller pair of scales. Both pairs are tuberculate. Gular scales number 6 - 8.
On the body the dorsal scales on the neck are smooth and in 25 - 29 rows. The first row is almost square; the scales become more lanceolate toward the vertebral line; the scales at mid-body are similar and in 26 - 28 rows but usually 27 rows; the scales at posterior body are similar and in 23 - 25 rows. The scales on the tail are similar to those on the dorsum. The ventral scales are 3-4 times wider than the height of a nearby dorsal scale. The ventral scales in 11 males ranged from 140 - 151 (X¯ = 145.8); and in five females ventral scale counts ranged from 140 - 151 (X¯ = 145.8). Several of the specimens examined had ventral scales that were divided. The anal plate is divided and it is about 1.5 times the length of the preceding ventral.
On the tail the subcaudal scales in 11 male ranged from 44 - 51 (X¯ = 48.2); and in seven females ranged from 36 - 42 (X¯ = 37.8). The posterior of the body is slightly depressed. At the base of the tail the width is about 75% of the height.
Color and pattern on the crown of the head are uniform, the rostral and the first three upper labials are dark in color as is the crown. There are white spots on labial four and those labials posterior to it. The chin is white with black spots. The dorsum is dark with scattered light spots. There are short lateral crossbars. The mixture of dark blotches and white spots on the body produce a mottled appearance. The ventral scales have dark brown pigment on the anterior edge but it may also be centered or off to one side. The ventral side of the tail is uniform black.
Natural History. Nothing is known about this species habitat and diet. Litter size data: One specimen (USNM 30767) contained three eggs and has an SVL of 520 mm.