Monodon monoceros

Narwhals are medium-sized whales that live in the freezing Arctic Ocean near the North Pole. Males grow a long spiral tusk that can reach up to 10 feet long, and it is actually a giant tooth poking out of their upper lip! People call them the unicorns of the sea because of their amazing tusk.
A narwhal's tusk is covered in millions of tiny nerve endings, so it can sense changes in water temperature and saltiness like a built-in superpower antenna.
Treat it with respect, keep your distance, and tell a grown-up if you see one up close.
Always ask a grown-up before you touch any animal or plant. If something bites or stings you, tell an adult right away.
Source: NOAA Fisheries
Read more about the narwhal at Wikipedia.