Cantoria Girard, 1858, was described on the basis of a specimen from Singapore. The type species is the morphologically distinctive Cantoria violacea Girard. Girard’s mud snake has an exceptionally long, slender body, with dorsal scales in 19 rows at mid body; and ventral scale counts in the 234-284 range. And, in many ways its body form and coloration resembles the true sea snakes. Jong (1926) described Cantoria annulata from a specimen from Prins Hendrik-eiland, New Guinea which had 21 scale rows at mid body and ventral counts that range from 168–182. While the annulated mud snake, C. annulata has its nasal scales separated by the internasal (as does Girard’s mud snake), it also has the internasal in contact with the frontal scale, a character state unknown in other homalopsids. Given these differences as well as differences in feeding habits Girard’s Mud Snake feeds on pistol shrimp, while the annulated mud snake feeds on gobies (Voris & Murphy, 2002), Murphy (2011) placed Cantoria annulata in the new genus, Djokoiskandarus. The genus Cantoria is now restricted to the Sunda Shelf and adjacent coastal mainland Asia.Girard's Mangrove Snake, Cantoria violacea has also been called Cantor’s Water Snake (Wall, 1914) and the Yellow-banded Mangrove Snake (Whitaker, 1978). Cantoria violacea inhabits the Andaman Islands (India); and the mouths of the Irrawadi and Moulmein Rivers (Myanmar), and coastal west Thailand, peninsular Malaysia, and Singapore. There are literature records from Sumatra and Timor however Sumatran and Timor specimens are unknown. There is a specimen from Sarawak, Borneo, the type of Hydrodipsas elapiformis Peters. Thus, this species inhabits the Indochina Bioregion and the Sunda Shelf and Philippine Bioregions and it uses the mangrove and mud flat habitats. The 19 scale rows at midbody, the internasal which separates the nasal scales, the broad contact of the prefrontal scales, and the ventral count of more than 243 readily distinguish this species from all other homalopsids. Wall (1924) reported a 1220 mm specimen and Ghodke and Andrews (2002) estimated some specimens in the field at 1.5 m. Males have a long, thin, stringy, gracile appearance while females of the same size are more robust. Males have longer tails (18 - 21% of the SVL, = 20%) than females (12 - 17% of the SVL, = 13.7%). Cantoria violacea uses mangrove forests and mud flats, but will apparently use nearby freshwater environments on occasion (Rao et al., 1994). It seems to be associated with the intertidal burrow system which includes mud lobster mounds and crab burrows, and it is active at night. Smith (1943) described its habitat as "Tidal rivers and coasts..." Tweedie (1983) wrote, "This very long slender snake lives on coasts.” Two specimens from Phuket Island, Thailand, were collected in or near tidal creeks in mangrove forest on rising tides (Voris and Murphy, 2002). Ghodke and Andrews (2000) found it on mud flats in the Andaman Islands, with their posterior bodies in crab holes and they reported specimens in proximity to each other (0.5 - 6 m), in one case they described finding them in pairs. Karns et al. (2002) found violacea associated with mud lobster mounds and mud pools. Sworder (1923) considered this “A very rare snake.” in Singapore. This is undoubtedly due in part to its microhabitat, the intertidal burrow system, which is seldom explored by herpetologists, or other naturalists. However, Karns et al. (2002) found this species only three times (1.1% of the 270 snakes collected) at Pasar Ris Mangrove Park in Singapore, while Ghodke and Andrews (2002) considered it “fairly common” in the North Andaman Islands. Contrary to literature comments that this snake feeds on fish and crabs, Cantoria violacea appears to feed exclusively upon Alpheus shrimp (Crustacea: Decopoda: Alpheoidea). The stomach contents of FMNH 250115 consisted of one complete female giant mangrove snapping prawn, Alpheus microrhynchus (thorax length 20 mm, total length 57.5 mm, claw length 30.3 mm, weight 5.1 g); a second specimen, a male contained one complete but digested claw of a Alpheus microrhynchus (claw length 25.7 mm) and one digested decapod (probably the remains of another A. microrhynchus). Two Myanmar specimens also contained Alpheus: contained one ovigerous female Alpheus sp. and another had remains of three specimens of Alpheus euphrosyne euphrosyne (Voris and Murphy, 2002). Unfortunately there are no observations of feeding behavior in this species and its feeding adaptations may prove to be of interest. Alpheus shrimp (commonly known as snapping shrimp or pistil shrimp) have some unusual defense and communication behaviors and how these effect the feeding behavior of C. violacea is sure to be of interest. Alpheus produce a loud sound resulting from the collapse of a cavitation bubble in their enlarged pincer, and the collapsing bubble also produces a flash of light. Thus, C. violacea may use the light, the sound, a chemical spread via a stream of water coming from the claw, or a combination of these to detect and locate its prey. The venom chemistry of this species is completely unknown. However, Ghodke and Andrews (2000) reported stories from Karens living in the Andaman Islands who stated that they knew people who had been bitten by this snake, one had died, and another had been unconscious for several days. Bite symptoms included abdominal pain, vomiting blood and swelling at the site of the bite. A folk remedy made from a “cactus-like plant that grows in mangroves” was applied to the bite lesions and taken internally. They acknowledged that Cantoria is usually considered harmless and that it has a similar appearance to the Andaman krait (Bungarus andamanensis).
- Ghodke, S. and H. V. Andrews 2002. Recent record of Cantoria violacea (Girard, 1857) from North and Middle Andaman Islands, India with a note on its bite. Hamadryad 26:372-373.
- Karns, D. R., H. K. Voris, T. G. Goodwin. 2002. Ecology of the Oriental-Australian rear-fanged water snakes (Colubridae: Homalopsidae) in the Pasir Ris Park Mangrove Forest, Singapore. The Raffles Bulletin of Zoology 50:487-498.
- Murphy, JC. 2011. The nomenclature and systematic of some Australasian homalopsid snakes (Squamata: Serpentes: Homalopsidae). The Raffles Bulletin of Zoology 59, 229–236.
- Smith, M. A. 1943. The Fauna of British India, Ceylon and Burma. Reptilia and Amphibia. Vol. 3. Serpentes. London: Taylor and Francis.
- Sworder, G. H. 1923. A list of the snakes of Singapore Island. Singapore Naturalist 2:55-73.
- Tweedie, M. W. F. 1983. The Snakes of Malaya. Singapore: Government Printers.
- Voris, H. K. and J. C. Murphy. 2002. Prey and predators of homalopsine snakes. Journal of Natural History 36(13):1621-1632.
- Wall, F. 1914. Occurrence of Cantor's watersnake (Cantoria violacea) in the Andamans. Journal of the Bombay Natural History Society 23:166.
- Whitaker, R. 1978. Common Indian Snakes, A Field Guide. Dehli: MacMillian India Ltd.
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