VII. Family Hydrophidae

All sea snakes belong to this family are aquatic and form 2.8 % of all the known snakes. These snakes are different from land snakes in their body pattern, feeding and courtship behaviours. They are larger in size than their terrestrial relatives except pythons. Their length varies from 1150 - 1550 mm, the maximum recorded length which has been recorded is nearly 2700 mm.

All snakes of this family are deadly venomous and their venom is neurotoxic in nature. Their body is cylindrical and the head is covered with large scales. The eyes are small with round pupil and nostrils are present on the dorsal surface of the head. The tail is flat and oar like, this special modification helps them to swim. The ventral scales are small. Unlike Vipers, maxillary teeth, short maxillary bones and poisonous fangs are present and are fixed to the front part of the upper jaw.

These sea snakes possess lungs and thus keep their nostrils above the water surface for oxygen, though they can survive under water without oxygen for 7 - 8 hours. The left lung is large and travels the whole length of the body. The posterior part of the lungs keeps their bodies in balance during swimming.

These sea snakes are found abundantly at the equator and prefer bays and coastal areas. They mainly inhabit shallow water and only explore the depth in search of food. Most of them spend their whole life in salt water but a few species may prowl the nearby land. They can swim very fast but cannot move on the land with such speed and ease. Fishes, crabs, shrimps and other crustaceans are their preferred food.

The breeding season varies from specie to specie and depends on the temperature of the water. All sea snakes are viviparous and give birth to their young ones in mangrove swamps. Normally a female gives birth to 3 -16 young ones at a time.

They are widely distributed and inhabit almost all the oceans of the world. In Pakistan, 7 genera and 14 species of this family are found. which are as follows: