A story about the diversity and features of the external structure of animals?

The variety of animals on our planet is very large. Scientists count up to four million species, but this number can be very inaccurate. They all have their own adaptations to the environment. This can be the shape of the body, the presence or absence of limbs, the presence of a head and sensory organs, the presence of hair or its absence. There are a huge number of such devices. They were formed in the process of evolution and are necessary to simplify the life of an animal, protect it from irritants and many other functions.