This species of whale is best known for its tusk—a long, spiraled tooth that usually only the males develop. (Females occasionally do.) The tusk can grow to 9 feet (3 meters) long and weigh more than 22 pounds (10 kilograms).
Scientists don’t know exactly why narwhals have tusks—though they might be used to impress females or fight other males. But tusks are more than battle swords—they're packed with nerves and covered in tiny holes that allow seawater to enter. This gives tusks a sensitivity that could help narwhals detect changes in their environment such as temperature or even the water's saltiness. Clues like these might help narwhals find prey or survive in other ways.
Narwhals' Arctic habitat makes them difficult to study, and scientists still have plenty to learn about them. These unicorns of the sea might be mysterious, but they're certainly no myth.