In truth, birds are the only class of animals that have feathers. Even though all kinds of birds begin life as an egg and most birds fly, different courses of animals also share those characteristics. There are over 33,600 estimated species of fish that live in bodies of water from shallow ponds to the deepest components of the ocean. According to some estimates, there are extra species of fish than another class of vertebrates on the planet. Although vertebrates contain the greatest number of animal lessons, invertebrates are the most typical species of animals in the world.