Most widely distributed snake

No other species of snake has a greater range than the pelagic seasnake, or black and yellow seasnake or yellow-bellied seasnake (Hydrophis platurus). It is found in tropical regions of both the Pacific and Indian oceans, from the east coast of Africa and the Persian Gulf, throughout south-east Asia and the waters off Australia, across to California, USA, and Ecuador in South America. It is among the most aquatic and pelagic of all seasnakes, spending much of its life in the open ocean, exploiting surface currents to travel great distances and never needing to venture on land or the seafloor.

In the eastern Pacific, the pelagic seasnake has been observed as far north as Possiet Bay, Russia (42.7°N) and as far south as Wellington, New Zealand (41.3°S); in the western Pacific, the range extends from San Clemente, California, USA (33.6°N) and Chile's Easter Island (27.1°S).

Until recently, this snake occupied its own monotypic genus, Pelamis, but it has now been placed within the wider seasnake genus Hydrophis.