International Wildlife Encyclopedia - Vol. 17

International Wildlife Encyclopedia - Vol. 17

International Wildlife Encyclopedia - Vol. 17

International Wildlife Encyclopedia - Vol. 17

Excerpt

SEA SNAKE

SEA SNAKES ARE REPTILES that have returned to the sea from the land and have mostly become fully adapted for life in the water. They differ from land snakes in having the body flattened from side to side, with a flattened, paddle-shaped tail that is used for propulsion.

There are two main groups of sea snakes. [True] sea snakes are believed to have evolved from land-living, venomous snakes from Australia, and are still placed in the same family as cobras by some zoologists. There are about 50 species. They are highly adapted to the marine environment, having nostrils located on the top of the snout so that they can breathe when most of the head is under water. Females produce well developed young without laying external eggs, so they do not need to return to land to breed. The nostrils can be closed by valves that prevent water from entering when the snake dives. As in most snakes there is only one lung, and this extends for most of the length of the body to provide buoyancy. Glands near the base of the tongue excrete salt that the snake takes in from the surrounding sea, and the snakes can breathe to a certain extent through their skins, although they cannot entirely rely on this method. Though they swim gracefully when they are in the water, true sea snakes are almost helpless on land because the scales on their undersides are very small and do not provide grip. They never leave the water voluntarily.

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