Narwhals, also called unicorns of the sea, live in very close contact with the Arctic sea ice. Their characteristic tooth, which grows from their forehead at the age of 2, is continuously growing and can reach up to 3 meters long (9,8ft). This canine contains around 40 millions nerve endings able to determine pressure variations, temperature changes and salinity of the water. A precious tool for this animal that plunges all winter, to depths exceeding 1,500 meters (4,920 ft) to feed.