They therefore breathe air but cannot survive on land. Some species are very large indeed and the blue whale, which can exceed 30m in lengh, is the largest animal to have lived on earth. Superficially, the whale looks rather like a fish, but there are important di.fferences in its external structure. Its tail consists of a pair of broad, flat, horizontal paddles (the tail of a fish is vertical) and it has a single nostril on top of its large, broad head. The skin is smooth and shiny and beneath it lies a layer of fat (blubber). This is up to 30cm in thickness and serves to conserve heat and body fluids.
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