英语科普：鲸鱼不是鱼

鲸鱼不是鱼，而是整个一生都生活在水里的哺乳动物。
Whale is the common name for various marine¹ mammals of the order Cetacea. Whales breathe air and are not fish. They are mammals that spend their entire lives in the water. Whales are of two types: toothehed (Odontoceti) and balleen (Mysticeti) whales.

 

The anatomy² of whales can be described as follows:

 

Like all mammals, whales breathe air,

They are warm-blooded,

They nurse their young with milk from mammary glands³,

They have body hair.

Beneath the skin lies a layer of fat called blubber, which stores energy and insulates the body.

Whales have a spinal⁴ column, a vestigial pelvic bone,

Whales have a four-chambered heart.

The neck vertebrae are typically fused, trading flexibility⁵ for stability during swimming.

Whales breathe via blowholes; baleen⁶ whales have two and toothed whales have one. These are located on the top of the head, allowing the animal to remain almost completely submerged whilst breathing. Breathing involves expelling excess water from the blowhole, forming an upward spout⁷, followed by inhaling⁸ air into the lungs. Spout shapes differ among species and can help with identification.

 

The largest whales are blue whales. In fact, the blue whale is the largest animal known to have ever existed at 30 m (98 ft) and 180 tonnes. These huge animals eat about 4 tons of tiny krill each day, obtained by filter feeding through baleen, a comb-like structure that filters the baleen whales' food from the water.

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