Hi @Frithjof Moritzen, I'm glad to hear from someone who has seen Tuatara. I came across Tuatara's third eye when searching for less-known animals with peculiar features.

Wikipedia article (https://en.wikipedia.org/wiki/Tuatara) has this:

"The tuatara has a third eye on the top of its head called the parietal eye. It has its own lens, a parietal plug which resembles a cornea,[48] retina with rod-like structures, and degenerated nerve connection to the brain. The parietal eye is visible only in hatchlings, which have a translucent patch at the top centre of the skull. After four to six months, it becomes covered with opaque scales and pigment"

I now understand it is a less-known fact. It might confuse people who have seen Tuatara. Thanks for letting me know.