Bitia hydroides
(Petrova) 
Malaysia (© M.A. Muin) 
Malaysia (© M.A. Muin) 
Malaysia (© M.A. Muin)
English name: Keel-bellied Water Snake
Scientific name: Bitia hydroides
Thai name: งูปากกวางทองสัน (Ngu Pak-Kwang Tong San)
Description: To 90 cm long. Body is of average girth. Head is somewhat distinct from the neck with bulging grey eyes. Color is light grayish turning to yellow on the top with long band-like black blotches. Tail is short and narrows quickly to a point. Belly is white/cream.
Relevant scale counts: 37-43 midbody scale rows, dorsal scales are small with gaps that show skin between them. Belly scales are keeled.
Similar Species: Cantor’s Water Snake is more slender with a smaller head, is mostly black with narrower yellow bands, and has quite different scales.
Dog-faced Water Snake has a more distinct head with fleshy cheeks, larger scales without the gaps, and a darker upper body.
Martaban Water Snake has a more distinct head, light saddle blotches on a dark background, no skin between the scales, and a longer tail.
Little Wart Snake is heavy-bodied with full bands more even in width and skin that hangs loosely.
Sea Snakes have blunter, more paddle-like tails that don’t narrow down to an elongated point. Never pick up any snake, especially in the ocean, unless you are absolutely sure of its identification.
Range: The Keel-bellied Water Snake is known from the Andaman Sea coasts of Myanmar, Thailand, and Malaysia as well as the Straits of Malacca including Singapore. There is only a single record from Bangkok, it may not be a regular resident of the Gulf of Thailand.
Habitat: This species is only found in coastal river mouths and nearby mudflats, though it is possible that they hunt in deeper waters. They are proficient burrowers and spend most of their time in the mud.
Place in the ecosystem: Eats fish in the mudflats, especially mudskippers (gobies). May be eaten by larger snakes, monitors, crocodiles, large fish, or wading birds.
Danger to humans: This rear-fanged species is quite similar to a sea snake in appearance, but completely harmless to humans.
Conservation status and threats: Less than 200 specimens of the Keel-bellied Water Snake have ever been found. However, those specimens were found over a wide range, and in at least one locality were extremely common (over 100 of the snakes found in a few months). It is believed that the Keel-bellied Water Snake is simply difficult to locate rather than rare, but the infrequent observations of the species make it impossible to determine its true abundance.
Interesting facts: The Keel-bellied Water Snake has enlarged palentine teeth, an unusual characteristic shared by only one completely unrelated species of snake. The reason behind these enlarged teeth is unknown.
References:
IUCN Red List: Bitia hydroides
The Reptile Database: Bitia hydroides
Morphology, Reproduction, and Diet of the Marine Homalopsine Snake Bitia hydroides in Peninsular Malaysia
Michael Cota, Personal Communication
A Checklist and key to the Homolopsid snakes
Evolution in the Mud
Reptiles and Amphibians of Thailand 