Narwhal

Often called 'unicorns of the sea' due to the large horn-like tusk that grows from their foreheads, narwhals are ocean predators that live in the coldest waters. The tusk can grow to tremendous length, often longer than the narwhals body, and is used mostly for defense against larger predators such as sharks and polar bears.

Narwhals live in packs, helping one another and finding strength in numbers. They feed on fish smaller than themselves and the occasional freshly dead thing, and while their bodies can have many uses they are not actively hunted or domesticated. If something comes from a narwhal it's because someone came upon a corpse, or the occasional one caught in fishing nets is too injured to survive release, and in the arctic the motto of 'waste not, want not' is especially true. Fats and oils can help lanterns burn, the meat is edible if cooked, and the horns can be broken or sawn off for makeshift weapons or fire skewers.