skeletal
The narwhal is an odontocete or toothed whale, but unlike all other toothed whales it has no teeth in its mouth. Instead, the male develops a long straight tooth (or tusk) that protrudes 2-3 m out of the upper left jaw. The tooth grows in a counterclockwise spiral. The tusk is unique to male narwhals. Very rarely, a female will grow a tusk, or a narwhal will grow two tusks.
muscular
The Arctic-living tusked whales are exceptional endurance athletes, possessing a greater density of slow-twitch fibres in their muscles than any other marine mammal studied.But this ability also means they are one of the sea's slowest swimmers.In narwhals, around 87% of their swimming muscle fibres are of the slow twitch variety, which respond slowly but do not tire easily.