Tuesday, April 7, 2015

Sarawak Mud Snake, Homalophis doriae Peters, 1871

Homalophis doriae Peters, 1871: 577. Syntypes, MSNG CE 30665 and ZMB 7120.  Type Locality: Sarawak, Borneo.

Hypsirhina doriae: Boulenger, 1893, 3: 13.

Enhydris doriae: Haas, 1950: 576.

Diagnosis. Dorsal scales in 29–33 rows at mid-body; suboculars present; 11–16 upper labials with last 5–9 horizontally divided. It may be most easily confused with H. gyii, which has 25–27 scale rows at mid–body and more than 153 ventrals.

Distribution. Known only from Borneo (Murphy, 2007).

Etymology. Enhydris doriae is named after the 19th–century Genoese nobleman, the Marquis Doria, who supported numerous collecting expeditions into Southeast Asia (Stuebing and Inger, 1999) and collected the syntypes of this species. Common name. Blotch-Lipped Mud Snake (Stuebing and Inger, 1999).

Distribution.    This species is known only from the island of Borneo; most specimens are from the Malaysian states of Sabah and Sarawak, and I have seen one specimen from Kalimantan. Shelford (1901) reported it from Kuching [Sarawak], Borneo; and Stuebing (1991) listed the following localities: Sabah: Sandakan Bay; Sarawak: Baram, Kuching, Labag, Mengion Rivers. Iskandar (2004) reported it from eastern Kalimantan in the area bordered by the Seturan and Rian Rivers.

Diagnosis. A species with: 29 – 33 scale rows at midbody; subocular scales; 11 – 16 upper labials, with the last five to nine horizontally divided; and 137 – 152 ventral scales. This snake may be most easily mistaken for its close relative Enhydris gyii which also has subocular scales, but has 25 or 27 scale rows at midbody and more than 153 ventral scales. Other taxa with 29 – 33 scale rows lack subocular scales, except Homalopsis buccata which has strongly keeled and striated scales, but it usually has more than 33 scale rows at midbody. Cerberus may on occasion have this number of scale rows, but it has fragmented parietal scales.

Size. The largest specimen measured was a female with a total length of 797 mm and a 101 mm tail. Female SVLs ranged from 193 – 695 mm. The largest male had a total length of 705 mm and 125 mm tail. Male SVL’s ranged from 175 – 580 mm. Near full term embryos were 181 – 197 mm in total length, this is similar to the size of some neonates measured. Gyi (1970) also noted sexual dimorphism in tail lengths; in this study males had tails that are 20 – 26% of the SVL, while females had tails that are 14 – 18% of the SVL.

External Morphology. Head is distinct from neck, the body is slightly depressed. The tail is flattened. The eyes are dorsolateral, and the orbit's diameter is about twice the eye–nostril distance.
            On the head the scales shows an extraordinary trend toward fragmentation, and scale numbers and shapes are highly variable in traditional scale counts for a colubrid snake. The rostral scale is pentagonal, slightly broader than tall, and visible from above, and it is often tuberculate. The nasals are in contact, each is larger than the rostral, and much larger than the internasals. They are divided with the cleft touching the internasals or divided with the cleft touching the second labial, or sometimes the first labial. The first two or three upper labials are in contact with the nasals. The internasal scales are posterior and slightly penetrate the nasals on the seam, and they are about half the size of the nasals. The prefrontal scales are in broad contact with the loreal, and they are about the same size as the nasals. The length of the frontal is equal to or less than the interorbital distance. The parietals are as long as or longer than the frontal. The loreal is single, rarely double; it is about twice as long as high and in contact with labials 2 – 5, 2 – 6, or 3 – 7. The supraocular scales number 1 – 4; the middle scale(s) is/are the smallest; the most posterior is usually the largest. Of  22 specimens examined (44 sides) the frequency of one supraocular was 4.5%, the frequency of two supraocular scales was 16%, the frequency of three supraocular scales was 73%, the frequency of four supraocular scales was 7%. The preocular is single (rarely double 11%). The postocular scales may number two (88.6%) or three (11.4%). The subocular scales number 2 – 5 with the following frequency two (21.8%), three (43.7%), four (25%), five (9.3%). The temporal formula is 1 + 2 or 2 + 2 with the tertiary row indistinguishable from the occipitals and even the primary and secondary rows tend to be small. Upper labials number 11 – 16. The sixth or seventh and beyond are divided into 2 – 4 tiers of scales. Upper labials 7 – 8 or 7 – 8 – 9 are usually under the orbit but separated from it by the subocular scales. The anterior six labials are very narrow and imbricate. In seven (31%) of 22 specimens all of the upper labials were divided.
            On the chin the lower labials number 14 – 18 with most specimens having 15 – 16. The first 2 –5 are in contact with the anterior chin shields. The second lower labial is usually the largest. The first two lower labials form the mental groove. The anterior pair of chin shields is in contact with the 2 – 5 or 2 – 6 lower labials. They are larger than the second pair and tend to be elongated and boomerang–shaped. The second pair is separated by a smaller pair of scales. Chin shield pairs may number 2 – 4 with the anterior pair being the largest. The gulars number 6 – 12.
            On the body the dorsal scales on the neck are in 29 – 33 rows; of 22 specimens examined 7% had 29 rows, 54% had 31 rows, and 36% had 33 rows. The first row is ovate and the scales become more elongated toward the midline of the body. Dorsal scales at mid-body are the same as above and number 29 – 31, in 22 specimens 13% had 29 rows, 72% had 31 rows, and 13% had 33 rows. Dorsal scales rows near the vent are reduced to 25 – 27, and they also change from ovate to elongate from first row to midline. The ventral scales are about 3.5 times as wide as the height of a nearby dorsal scale and numbered 137 – 152 (males 139 – 146, females 137 – 152). The anal plate is divided and slightly longer than the preceding ventral scale.
            On the tail the dorsal scales are ovate and striated. The subcaudal scales are divided and number 39 – 60. Thirteen males had 46 – 60 subcaudal scale counts, eight females had 39 – 44; thus the subcaudal counts are sexually dimorphic. At the base of the tail the width is 83% of the height, based on an average of five specimens.
            Color and Pattern. The dorsum is a slate gray, including the crown of the head and the tip of the chin. The first 4 – 5 scale rows are uniform cream, yellow or pink, which is the same color as the venter. In some specimens scattered dark blotches of pigment occur on the ventral side and in one specimen (MCZ 5240) each ventral is darkly pigmented with a light posterior margin.
Habitat. Stuebing and Inger (1999) stated that it is found exclusively in swampy habitats and muddy rivers below 500 m in coastal Sarawak and Sabah. Voris and Karns (1996) collected one from a fisherman’s trap set in a stream in Kayumadang, Sabah, Malaysia. Iskandar (2004) stated that it can be abundant in stagnant or slow moving water of rice fields and ponds.

Diet and Feeding Behavior. Apparently this species is piscivorous, Iskandar (2004) stated that it feeds on fish, is caught in fish nets, and is considered a pest by aquaculturists in eastern Kalimantan.

Reproduction. Three gravid females contained 6 – 16 eggs or embryos (= 9.6). FMNH 14920 is a 645 mm SVL (total length 706 mm) female with 16 embryos that are 100 – 120 mm in total length. Embryos still had umbilical cords attached but no yolks. It was collected 16 August near mile 8 Sandakan, Sabah. Another specimen (RMNH 4339) has a 550 mm SVL and contained seven eggs. Sabah Museum RE0.0322 is a 574 mm female (weight without embryos is 135.5 g) with most of the tail missing; she contained six embryos that were 181 – 197 mm in total length (= 190.6 mm) and they weighed 4.7 – 6.5g (= 5.25 g).



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