Added April 20 2003. Last updated 20 April 2007: added a link to Hydrophis.

The Hydrophiidae

The Hydrophiidae is a family comprising species that live a mainly or completely aquatic existence. Most are found in the area between the Persian Gulf and the seas and oceans around the Indoaustralian archipelago, with a few reaching the Pacific coasts of the Americas: none are recorded from the Atlantic or Eurasian waters. Only two species are known to live in freshwater bodies, and it seems that these were trapped there long ago. The most obvious distinguishing mark of many of them is their paddle-like tail, while less obvious but equally important characteristics include valvular muscles that allow nostrils and lingua fossa (notch for the tongue) to be closed, and viviparity (live birth). Most also lack the enlarged ventral scales that allow other snakes to move about on land, and hence are rather helpless out of the water.

The relationship of the Hydrophiidae to the Elapidae and Viperidae has been closely examined in recent years, and a number of alternative taxonomic arrangements proposed, most of which seem to involve demoting the Hydrophiidae to a subfamily of the Elapidae. However, since no one formula has yet been agreed on, and the sea snakes have such obvious physiological differences to meet their unique way of life, the traditional arrangement looks set to stay around for a while longer. Within the sea snakes themselves there are two divisions: subfamily Laticaudinae, which contains one genus of 5 species, all of which are capable of reasonable terrestrial locomotion and which come ashore to lay their eggs, and subfamily Hydrophiinae, which contains all other sea snakes.

While the venom of most sea snakes is extremely toxic, it is interesting to note that most (but not all!) are also extremely docile and do not seem to react adversely even when handled. However, divers coming across these creatures in close proximity are still advised to be cautious. In some cases the natural curiosity of some species, eg Aipysurus laevis, is interpreted as aggression by humans (Cogger).

Family Hydrophiidae

Genus Common Name Distribution Size Notes
Subfamily Hydrophiinae
Acalyptophis Spiny-Headed Sea Snake China, Burma, Vietnam and Tibet 1m 1 species, A. peronii: toxicity unavailable.
Aipysurus   W Australia to New Caledonia and Loyalty Islands 2-3'   8 species. This genus, unusually, does have enlarged ventral scales allowing them to move on land, although they give birth in water. A. duboisii, A. eydouxii, A. laevis and A. tenuis are considered DANGEROUS.
Astrotia Stoke's Sea Snake Indian Ocean to China Sea, SE Asia and Indoaustralian archipelago 3-6'   1 species: DANGEROUS
Disteira   Persian Gulf, Indian Ocean and Australian waters 1.3- 1.5m? 4 species. The 2 Australian species at least are usually found in deeper waters and are DANGEROUS.
Emydocephalus Turtle-Headed Sea Snakes Indonesian and Australian waters, SE Asian sea 75cm? 2 species. Measurement applies to Australian species, which feeds exclusively on fish eggs on reefs. Both species have enlarged ventral scales allowing them to move on land, although they give birth in the water. Toxicity of SE Asian species not known.
Enhydrina Beaked Sea Snakes Indian subcontinent, SE Asia and China 1.2m 2 species: Australian species is aggressive and DANGEROUS.
Ephalophis ?? Australia (NT and WA) 50cm 1 species, E. greyae, found in mangroves and associated mudflats, especially in estuaries.
Hydrelaps Port Darwin Sea Snake  Coral Sea, Australia   1 species, H. darwiniensis, found mainly in mud flats associated with mangroves [Cogger]. 
Hydrophis   Indoaustralian and SE Asian waters .5-1.5m 29 species, of which all the Australian ones at least are DANGEROUS. 
Kerilia ?? SE Asian waters ?" 1 species, K. jerdoni: toxicity unavailable.
Kolpophis ?? Indian Ocean   1 species, K. annandalei: toxicity unavailable.
Lapemis ?? Persian Gulf to Indian Ocean, S China Sea, Indo-Australian archipelago and W Pacific 1m  2 species: DANGEROUS. 
Pailsus   Australia (N Queensland) ?" 1 species, P. pailsei. It is not recorded in Cogger and its authenticity is questioned by the EMBL reptile database. If it is synonymous with Pseudechis australis as suggested, then it should be considered DANGEROUS.
Parahydrophis Arafura Smooth or Mangrove Sea Snake  Arafura Basin between New Guinea and Australia 50cm 1 species, P. mertoni: encountered in coastal and estuarine mangroves and associated mud flats.
Parapistocalumus Bougainville/ Hediger's Coral Snake Papua New Guinea and Solomon Islands   1 species, P. hedigeri: toxicity unavailable.
Pelamis Yellow-Bellied Sea Snake  E Africa and Persian Gulf through S China Sea and Indoaustralian archipelago as far as C & N S America   1 species, P. platurus: the most widely distributed of all sea snakes. Distinctive yellow and black longitudinal stripe pattern make this species unmistakeable. DANGEROUS.
Praescutata       No information available.
Thalassophina ?? Persian Gulf, Indian Ocean, SE Asia and Indonesia   1 species, T. viperina: toxicity unavailable.
Thalassophis   S China Sea and Indian Ocean   1 species, T. anomalus: toxicity unavailable.
Subfamily Laticaudinae
Laticauda ?? Mainly SE Asian and Indoaustralian waters, but 1 species reaches as far as the Americas. 1- 1.5m? 5 species. All are capable of terrestrial movement and lay eggs on land.

Bibliography

Snakes of the World, Chris Mattison, Blandford. Very concise and useful guide to the general biology, natural history and classification of snakes, including an overview of virtually all the world's species.

Reptiles and Amphibians of Australia, Harold Cogger, 6th edition, Reed New Holland, Australia, 2000. Indispensable guide for an overview and identification details of all Australian herptiles, including the many sea snakes found around the continent.

Field Guide to Snakes and Other Reptiles of Southern Africa, Bill Branch, Struik, S Africa 1998. Excellent field guide to the reptiles of the subcontinent, giving colour plates and scalation details for each species (and ecology where possible).

A Field Guide to the Reptiles of East Africa, Stephen Spawls, Kim Howell, Robert Drewes and James Ashe, Academic Press, 2002. Excellent field guide to the reptiles of the region.

Links

The EMBL reptile database has been especially useful for the latest records of the numbers of species in each genus and their distribution.

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