Tuesday, March 29, 2016

Cerberus microlepis Boulenger, 1896

     Cerberus cinereus Gray, 1849 (in part), Catalogue of the Specimens of Snakes in the Collection of the British Museum, p. 64.

Cerberus microlepis Boulenger, 1896 Catalogue of Snakes in the British Museum, 3:18. Type locality: "Philippines." Collector: H. Cumming. Syntypes: BMNH 1946.1.7.24-25. Types of Cerberus cinereus Gray (in part).   Taylor (1922) stated that the exact localities of the syntypes are no longer known. He also stated that Griffin reported a specimen from Camiguin, Babuyan Islands. Taylor looked at the specimen, a head only, which had the first three lower labials touching the chin shields; this information is not diagnostic for the taxon. Based upon recently collected material it seems reasonable to restrict the type locality to Luzon Island, and to the vicinity of Lake Buhi.

 Hurria microlepis - Taylor, 1922 The Snakes of the Philippine Islands, Manila, p. 114.

Etymology: The name microlepis is derived from the Greek mikros meaning “small” and from the Greek lepisma meaning “scale.” Thus this name refers to small scales, possibly to the fragmented frontal scale which is usually composed of small scales.

Distribution: Cerberus microlepis is known only from Luzon Island, Philippines. It may be restricted to the Lake Buhi area. Lake Buhi, a freshwater lake, was apparently formed in 1641 when an earthquake caused part of Mt. Iriga to collapse and form a dam (Karns et al., 2000). C. microlepis inhabits the Sunda Shelf and Philippine Bioregion of Wikramanayake et al. (2002).

Diagnosis: The larger number of dorsal scale rows at midbody will distinguish this species from the other members of the genus. C. microlepis has 27 - 29 rows at midbody while other species in the genus have 21 - 25 rows at midbody. This species also tends to have very numerous, large, well define tubercles on most of its scales, and a higher ventral count (159 - 172) than other Cerberus species.

Size: The largest individual measured for this work was a female with a total length of 1046 mm, and a 161 mm tail. The largest male measured had a total length of 768 mm with a 158 mm tail. Eight males had tails that were 23 - 27% of the SVL, and eight females had tails that were 18 -22% of the SVL.

External Morphology: The head is only slightly wider than the neck. The overall body shape is cylindrical in cross section and relatively elongated. The eyes are small, dorsal, and round. The lower jaw is not countersunk.
            On the head the rostral scale is about as broad as high and visible from above . The nasals are divided by the nasal cleft that touches the first labials and the internasals. The nasals contact each other and are slightly penetrated by the internasal scales. The internasal is divided and each is smaller than the prefrontal scales. The prefrontal scales contact the loreal, the upper preocular, and the supraocular. The frontal is fragmented into at least three scales and the largest portion is shorter in length than the supraocular in the 16 specimens examined . The parietals are fragmented, usually into numerous smaller scales, but on occasion into just a few larger scales. The loreal is usually single but may be divided, and it is in contact with the first four upper labials (rarely three). Each supraocular is in contact with part of the fragmented frontal. The preocular may be single or divided into two scales. Subocular scales usually number two on each side. There are often two postoculars on each side. There is one primary temporal, excluding the larger fragmented portions of the parietals. Upper labials number 9 - 10, the seventh is usually the largest, number 5 or 5 - 6 are under the orbit but do not enter the orbit because of the subocular scales. The last large upper labial is horizontally divided. All of the head shields are covered with numerous, large tubercles.
            On the chin lower labials number 13 - 15, the first and the seventh are the largest. The first three contact the first pair of chin shields. There are three pairs of enlarged chin shields; the most anterior pair is the longest. There are 7 - 8 gular scales between the chin shields and the first ventral scales that are divided.
            On the body scales on the anterior tend to be ovate in the first few rows and become more elongated near the midline. They are keeled, striated, tuberculate, and imbricate.  Scale rows on the neck usually number 29, although one specimen (USNM 197697) has 32, and a few specimens have 28. The dorsal scales decrease in height from row one to the midline. Scales in the middle of the body are similar to the ones on the anterior; they are keeled, striated and tuberculate. They are usually in 29 rows, although two specimens (of 16) have 31 at midbody and two have 28. In front of the vent dorsal scale rows are usually reduced to 21, but may number 23 - 25. The ventral scales on the anterior of the body are tuberculate and have rounded edges. Each has a black spot located on the anterior portion of the scale. The middle ventral scales are wider, but are still tuberculate and spotted. The ventral scales number 159 - 172. Eight males have 160 - 172 ventral scales; eight females have 159 - 166 ventral scales. The anal plate is divided and tuberculate.
            On the tail scales on the dorsum are similar to the other dorsal scales, but slightly more ovate. The subcaudal scales are divided and number 54 - 70. Eight males have 60 - 70 subcaudal scales, eight females have 54 - 61 subcaudal scales, and thus the subcaudal scale counts are most likely sexually dimorphic.
            Color and Pattern. The upper labials are dark brown with some light spots along the seams. The lower labials are yellow with dark areas on the mental and some dark spots on the lower labials. The chin, gulars, and anterior ventral scales are yellow. There is a dark spot at the corner of the mouth. There are five indistinct stripes on the neck followed by about 40 indistinct dark crossbars; each crossbar is 1 - 2 scales wide. The first two scale rows are yellow-brown forming a ventrolateral stripe. The dorsum is otherwise brown. The ventral side has a dark stripe formed by a dark brown blotch in the center of each ventral scale. The underside of the tail is dark with scattered light spots. The dorsum of the tail is uniform brown with indistinct dark crossbars. 

Natural History: Collectors’ notes accompanying specimens report this species in the shallow water of fish ponds at 1940 - 0100 hours.

Relationships: Karns et al. (2000) used sequences of mtDNA genes 12s, 16s, and cytand suggested that this species is derived from other Cerberus populations in the Philippines. In a follow-up study Alfaro et al. (2004) found that the Polillo population was supported as the sister group to C. microlepis and the Silliman population. Polillo is a large island about 20 km off the eastern coast of Luzon and the two islands have been connected during times of lower sea levels.

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