Sea snake
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Sea snakes of several different species belong to a group related to the cobras but are aquatic rather than land dwelling. They are only moderately large, rarely exceeding 2 m in length, often with peculiarly small heads for their body-size. The body is compressed as an adaptation for swimming and the snakes are so thoroughly aquatic that they are either clumsy or helpless when brought ashore. Only genus Laticauda has the typical broad ventral scales of snakes, and it is often considered the least advanced of the sea snakes. Nevertheless, similar to cetaceans, their lungs still require them to surface occasionally to breathe. Oxygen uptake through the skin has been demonstrated in sea snakes.
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[edit] Distribution
Sea snakes are confined to the tropical oceans, chiefly the Indian ocean and the western Pacific ocean. The yellow-bellied sea snake, Pelamis platurus, extends to the eastern Pacific. The olive sea snake, Aipysurus laevis, tends to live in reefs.
[edit] Classification
Sea snakes are divided into two subfamilies, Laticaudinae and Hydrophiinae, with the former distinguished from other sea snakes by the fact they are amphibious (living on land and water), rather than aquatic (never leaving the water). Sea kraits are a type of sea snake. Sea kraits are oviparous, returning to land to lay their eggs, versus other ovoviviparous species that bear their young in the water (subfamily hydrophiinae, aquatic sea snakes). Amphibious sea kraits, members of subfamily laticaudinae, have specialized ventral scales for crawling on land. Unlike eels, sea snakes lack gills or fins, instead having scales and, while spending much of their time underwater, they must surface regularly to breathe.[1]
[edit] Venom
Sea snakes are venomous. They have short hollow fangs near the front of the upper jaw, and the poison acts on the nervous system like the related cobra's. Unlike land snakes, however, sea snakes are not inclined to bite, and as such are not harmful unless abused. Sea Snake venom is generally more toxic and dangerous than venom from land snakes.[2] However, Sea snakes have a less efficient venom injection apparatus as compared to land snakes, vipers or cobras. Antivenom is available commercially in Australia, made by CSL Limited it is active against all sea snake venoms.
All 50 or so species of sea snakes are venomous, and some are known to have venom ten times as strong as rattlesnake venom, making them among the most potentially venomous of all snakes. Fortunately for divers, they are usually quite docile. A sea snake's paddle-shaped tail is useful for swimming, but otherwise these reptiles look very much like their land cousins, even down to the forked tongue they use during their searches.
Most cases of people being bitten by sea snakes involve fishermen bitten when sorting through a catch from a net. The venom is composed of powerful neurotoxins (affecting the nervous system) and sometimes myotoxins (affecting skeletal muscles), with a fatal dose being about 1.5 milligrams. Most sea snakes can produce 10-15 mg of venom.
[edit] References
- Scubadoc's Diving Medicine Online: Sea Snakes http://www.scuba-doc.com/seasnks.htm
- Rasmussen AR (1997): Systematics of sea snakes; a critical review, Symp. Zool. Soc. London 70, 15-30
- Smith MA (1996): Monograph of the sea snakes (Hydrophiidae), British Museum of Natural History, London
- Voris HK (1977): A phylogeny of the sea snakes (Hydrophiidae), Fieldiana Zool. 70, 79-169
- Romulus Whitaker (1978). Common Indian Snakes: A Field Guide. Macmillan India Limited.
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