Most sea snakes grow to sizes between 1.2m and 1.4m, some can reach 2m or more.
Hydrophis cyanocinctus reach 2.5m to 3m.
They reach a weight of about 0.8 -1.3 kg, at a size of 1.8m.
In most cases, females are larger than males.

All sea snakes have paddle-like tails  and many have laterally compressed bodies – they look somewhat like eels.
However, unlike fish, they do not have gills and must come to the surface regularly to breathe.
Nevertheless, they are among the most completely aquatic of all air-breathing vertebrates.
Among this group are species with some of the most potent venoms of all snakes.
Some have gentle dispositions and bite only when provoked, while others are much more aggressive.

All snakes are good swimmers, but only real sea snakes live their whole lives in the ocean.
Not only do they live there, they eat there and even have their young right inside the water.
Most cannot live at all on land.
If they get forced onto land by a storm or powerful currents, they are unable to move.
Sea snakes have no scutes (special scales on snakes' bellies that help them grip and slither across the ground), so if a sea snake ends up on a beach, it is unable to slither back out to sea.
Instead, sea snakes have a paddle-shaped tail.
With its tail, the snake can swim well.

Sea snakes have special nostrils that can close when they go underwater and open when they come up to breathe, like the blowhole of a whale (scientists call these valved nostrils).
The nostrils are found high up on the head so that the entire snake can stay under the water when they come up to breathe.
In its search for food, a sea snake may remain under water for a long time.
To do this, sea snakes have evolved a single lung that almost is as long as the whole body.

Most sea snakes are able to breathe through their skin.
This is unusual for reptiles, because their skin is normally thick and scaly.
Experiments with the black-and-yellow sea snake, Pelamis platurus (a pelagic species), have shown that this species can get about 20% of its oxygen in this manner, which allows for longer dives.

Like other land animals that have adapted to life in a marine environment, sea snakes swallow considerably more salt than their relatives living on land.
They do this through their diet and when they inadvertently swallow sea water.
Kidney function in birds and reptiles is too weak to remove enough salt.
In birds, such as penguins, salt is removed through nasal glands.
The marine iguanas of the Galapagos Islands use the same mechanism.
Sea turtles have lacrimal glands that allow them to produce very salty tears.
But in sea snakes, glands under and around the tongue let them expel salt with their tongue action.
Most sea snakes grow to sizes between 1.2m and 1.4m, some can reach 2m or more. Hydrophis cyanocinctus reach 2.5m to 3m. They reach a weight of about 0.8 -1.3 kg, at a size of 1.8m. In most cases, females are larger than males.
All sea snakes have paddle-like tails  and many have laterally compressed bodies – they look somewhat like eels. However, unlike fish, they do not have gills and must come to the surface regularly to breathe. Nevertheless, they are among the most completely aquatic of all air-breathing vertebrates. Among this group are species with some of the most potent venoms of all snakes. Some have gentle dispositions and bite only when provoked, while others are much more aggressive.
All snakes are good swimmers, but only real sea snakes live their whole lives in the ocean. Not only do they live there, they eat there and even have their young right inside the water. Most cannot live at all on land. If they get forced onto land by a storm or powerful currents, they are unable to move. Sea snakes have no scutes (special scales on snakes' bellies that help them grip and slither across the ground), so if a sea snake ends up on a beach, it is unable to slither back out to sea. Instead, sea snakes have a paddle-shaped tail. With its tail, the snake can swim well.
Sea snakes have special nostrils that can close when they go underwater and open when they come up to breathe, like the blowhole of a whale (scientists call these valved nostrils). The nostrils are found high up on the head so that the entire snake can stay under the water when they come up to breathe. In its search for food, a sea snake may remain under water for a long time. To do this, sea snakes have evolved a single lung that almost is as long as the whole body.
Most sea snakes are able to breathe through their skin. This is unusual for reptiles, because their skin is normally thick and scaly. Experiments with the black-and-yellow sea snake, Pelamis platurus (a pelagic species), have shown that this species can get about 20% of its oxygen in this manner, which allows for longer dives.
Like other land animals that have adapted to life in a marine environment, sea snakes swallow considerably more salt than their relatives living on land. They do this through their diet and when they inadvertently swallow sea water. Kidney function in birds and reptiles is too weak to remove enough salt. In birds, such as penguins, salt is removed through nasal glands. The marine iguanas of the Galapagos Islands use the same mechanism. Sea turtles have lacrimal glands that allow them to produce very salty tears. But in sea snakes, glands under and around the tongue let them expel salt with their tongue action.
Sea snake