Nicknamed unicorn of the seas,these legendary animals have two teeth. In males, the more prominent tooth grows into a swordlike, spiral tusk up to 8.8 feet long.  Long regarded as a real defense, this one is in fact a sensory organ very useful to adapt to the environment in which the Narwhal evolves. The tusks are 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.