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(sea snakes), a family of poisonous snakes living in the tropical waters of the Indian and Pacific oceans. The body is up to 2.7 m long. Sea snakes are well adapted to aquatic life. The body, especially its posterior part, and the short tail are vertically flattened in an oarlike shape. The head is small and covered with large plates. The nostrils have valves that prevent water from entering the nasal cavity. The oral mucosa is rich in blood vessels and capable of absorbing oxygen that is dissolved in water, thus enabling sea snakes to remain under water for long periods. The paired poison fangs are located at the front of the upper jaws and are equipped with a poison-conducting canal. The poison is very toxic, especially to fish. Sea snakes feed mainly on fish; some eat fish roe. The majority bear live young, and in some species there is a primitive placenta. There are 16 genera (about 50 species), including Hydrophis and Laticauda.