A fish with a see-through head.
'To feed their young, females grow an extra layer of skin that's rich in fats. The young scrape this skin off with their teeth and eat it. To help them, they have a specialised set of teeth adapted to the job, which are replaced by more pointed adult teeth as they get older.'
And in other news, Unlikely Worlds's tweets have been listed by Time magazine as one of the best 140 Twitter feeds of 2013.