The narwhal an Arctic species of cetacean. It is rarely found south of latitude 70 degrees North. It is one of two species of whale in the Monodontidae family (the other is the beluga whale). The most conspicuous characteristic of male narwhals is their single extraordinarily long tusk, which is a tooth that projects from the left side of the upper jaw and forms a left-handed helix. The tusk can be up to 3 m (nearly 10 ft) long (compared with a body length of 4-5 m [13-16 ft]) and weigh up to 10 kg (22 lb). One in 500 males has two tusks, which occurs when the right tooth, normally small, also grows out. Although rare, a female narwhal may also produce a tusk. Narwhals are quick, active mammals which feed mainly on species of cod that reside under ice-enclosed seas. In some areas their diet seems to have adapted to include squid, shrimp, and various fish, such as schooling pelagic fish, halibut, and redfish. Narwhals normally congregrate in groups of about five to ten.