The narwhal (Monodon monoceros) is a unique and fascinating marine mammal known for its long, spiral tusk, which has earned it the nickname "unicorn of the sea." Narwhals are part of the cetacean family, which includes whales, dolphins, and porpoises. They are medium-sized whales, with males typically reaching lengths of 4 to 5.5 meters (13 to 18 feet), not including the tusk. Females are generally slightly smaller and do not usually have tusks.

The most distinctive feature of the narwhal is the male's tusk, a long, helical tooth that can grow up to 10 feet in length. This tusk is actually an elongated canine tooth that protrudes from the left side of the upper jaw. Scientists believe the tusk has multiple functions, including sensory perception, as it is filled with nerve endings. Males may also use their tusks in mating displays or to assert dominance. Some rare individuals can even have two tusks, though this is uncommon.

Narwhals are adapted to life in the Arctic and are known for their incredible diving abilities. They can dive to depths of 1,500 meters (4,900 feet) in search of food, holding their breath for up to 25 minutes. Their diet mainly consists of fish, squid, and shrimp, which they hunt in the deep, icy waters. Narwhals are social animals, typically found in groups called pods, which can range from a few individuals to several dozen. They communicate using a variety of clicks, whistles, and knocks, which help them navigate and locate prey in the dark waters of the Arctic.

The coloration of narwhals changes as they age. Calves are born with a bluish-gray color, which darkens to blue-black as they mature. Older narwhals may appear almost completely white. Narwhals have a limited range, primarily inhabiting the Arctic waters around Greenland, Canada, and Russia. They are well adapted to the extreme cold, with a thick layer of blubber that provides insulation.