Sunday, March 27, 2016

Pakistan Mud Snake, Mintonophis pakistanicus (Mertens, 1959)

Enhydris pakistanica Mertens, 1959: 117. Holotype: SMF 56340. Type locality: Jati, Sind, West Pakistan.

Mintonophis pakistanicus – Murphy and Voris, 2014:27.

Diagnosis: Dorsal scales smooth, in 29 rows at mid-body; 153–162 ventrals exceptionally narrow on anterior body, widening posteriorly; 8–9 upper labials, 4 or 4–5 in orbit; internasal divided contact loreal; loreal contacts upper labials 1–3; lower labials 11–12; chin shields absent (or exceptionally small), replaced by numerous small scales; tail exceptionally long, about 26.7% of SVL. The exceptionally narrow ventrals, absent or tiny chin shields, and long tail suggest this snake is highly derived and convergent with Erpeton.

Distribution: Extreme western edge of the family’s distribution in the Indus River delta of Pakistan.

Size. The largest female measured had a total length of 987 mm and a 208 mm tail. The largest male measured for this study had a total length 720 mm, and a 207 mm tail. Kahn (2002) reported 493 - 500 mm SVL, 203 - 210 mm tail. The tail on this snake is very long, probably the longest tail found on any Enhydris, and the longest of any homalopsid with the exception of Erpeton.  Males have tails that are 32 - 41% of the SVL, and female’s tails are 21 - 33% of the SVL. See Gyi’s figure 20. Khan (2002) described the tail as distally compressed and prehensile. At the base of the tail the width is 81% of the height based on the average of five specimens.

External Morphology. The head is depressed and small in proportion to the body. The body is cylindrical. Eyes are dorsolateral; the orbit diameter is about half of the eye-nostril distance.
            On the head the rostral is pentagonal, broader than tall, and visible from above. The nasals can be entire, semi-divided, or divided, and they slightly penetrate the internasal scales. The internasal is divided and is located behind the nasals, and at first glance they appear to be part of the nasals because they are smaller than the prefrontal scales. The prefrontal scales are in contact with the loreals. The prefrontal scales are vase shaped, with a bent neck, and are similar in shape to those of D. dussermieri.  Gyi (1970) has described this as “arched over the internasals.” The frontal length is less than the interorbital distance. The parietals are relatively short, about the same length as the frontal, and they show signs of fragmentation. The loreal is smaller than the internasal and in contact with the first three labials, as well as the nasal, internasal, and prefrontal. There is a single supraocular with a narrow anterior margin and broad posterior margin. The single preocular is taller than broad; the two postocular scales are unequal in size; the dorsal scale is slightly larger than the ventral scale; here are no subocular scales; the fourth or 4 - 5 upper labials enter the orbit. The upper labials number 7 - 8. The temporal formula is 2 + 3. The tertiary temporal scales are indistinguishable from the occipital scales.
            On the chin the lower labials number 9 - 12, with the first pair forming the mental groove. There are no enlarged chin shields. However, ZRC 2.3929 has a pair of scales that appear to be slightly enlarged. Gular scales number 12 - 21.
            On the body the dorsal scales are smooth and in 31 - 33 rows on the neck, 29 rows at mid-body and 23 - 27 rows near the vent. Kahn (2002) reported 27 - 31 scales at mid-body. The dorsal scales on the anterior body are smooth. The first row is ovate and they become more lanceolate (elongated) toward the midline. The dorsal scales at mid-body are ovate to the ninth row, on the tenth row they start to elongate, and all are smooth. The dorsal scales at posterior body are smooth, ovate in the first row, and elongate toward the midline. The very narrow ventral scales number 150-163 in 13 females and 156 - 168 in four males. The anterior ventral scales are about 1.25 times the height of a nearby dorsal scale; this applies to at least the first 30 ventral scales. Mid-body ventral scales are about three times the width of a nearby dorsal scale. But, the dorsal scales are very small. The posterior ventral scales are about 2.2 times the width of a nearby dorsal, and the last ventral scale is almost the same width as a dorsal scale. The anal plate is divided and is three or more times the width of the preceding ventral scale.
            On the tail the dorsal scales are smooth, ovate on the sides, and slightly more elongate on the dorsum. The subcaudal scales are paired, and number 82 - 92 in four males, and 70 - 81 in 13 females.
            Color and Pattern. On the crown of the head is uniform olive green. On the midline of the back (rows 12 - 16) there is a black stripe; rows 9 - 11 are olive-green; rows 6 - 8 have a black stripe; row five and part of row six are yellow; rows 3 - 4 are mottled black and yellow forming an irregular stripe; rows 1 - 2 are yellow. The ventral scales have a black stripe that covers most of each scale. The tail is mostly green with some traces of black and yellow stripes. The tail’s ventral surface has a continuation of the midline ventral stripe. The skin of these specimens is very oily.

Habitat. There are few literature comments on the habitat of this species. Minton (1966) wrote, "...large shallow ponds near channels of the Indus but not in the stream itself. Some of the sites are near brackish water, and one (Shah Bunder) was a seaport during the early Moslem period. Collectors report that the snakes are diurnal, almost entirely aquatic, and very shy. They have been taken from late April through November and are said to bury themselves in mud at the edge of the ponds with the approach of cool weather." And, Kahn (2002) stated that it, “Frequents seepage pools along water channels and ponds which are rich in emergent vegetation. Almost entirely aquatic, not known to venture away from water. Shy, buries in mud and hibernates during winter when water dries up.”

Diet. Kahn (2002) stated that it feeds on “fish, frogs, tadpoles and aquatic arthropods.” It is unclear if this is based upon observations of stomach contents or feeding habits of captive specimens.

Reproduction. Gyi (1970) reported AMNH 93154 contained 16 embryos; the SVL of this female is 708 mm. The RCM for the AMNH specimen is 0.373. The effort per embryo for the single litter is 4.8. CAS 99964 (500 mm SVL) contained eight embryos.

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