An extremely peculiar creature with a bulbous transparent head has been spotted by a diver in Bali.
There are some very strange-looking animals living in the depths of the world's oceans, as evidenced this week by a viral video showing a remarkable jelly-like sea slug.
The footage was recorded by a diver who admitted that he had no idea what it might be.
In the video, the animal can be seen inflating a bulbous balloon-like sack on its head which it apparently uses to scour the sea floor for smaller organisms to feed on.
Some Internet users have suggested that it could be a sea slug species known as Melibe viridis.