A true sea snake that cannot leave the water, and an inquisitive one.
To about 200 cm, heavy-bodied and olive to purple-brown, sometimes with pale-edged scales, with a small head, a flattened paddle tail and no broad belly scales — it cannot move on land and gives birth to live young at sea. Its range in the Coral Triangle sits mainly on the Australian and Papua New Guinean shelf; it is not among the sea snakes seen at the Indonesian and Philippine muck destinations.
It hunts fish and invertebrates in coral and rubble, and has light-sensitive receptors in the tail that appear to help it keep the tail hidden while its head is in a crevice. Individuals regularly approach divers closely and investigate, sometimes coiling around a limb or a hose; the behaviour is exploratory and is associated with courtship in males during the breeding season. It is venomous and a bite would be a medical emergency, though bites on divers are very rare. Recorded from about 3 to 40 m.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.