The narwhal is a unique marine mammal known for its long, spiral tusk, which can grow up to 10 feet in length. This tusk is actually an elongated tooth that protrudes from the upper jaw of male narwhals, and it is thought to play a role in mating displays and social interactions. The tusk is made of ivory and has sensory capabilities, allowing the narwhal to detect changes in its environment. While often referred to as a "unicorn of the sea," the narwhal's tusk has also been historically sought after for its beauty and rarity, leading to concerns about overexploitation.