+Introduction to the animal kingdom+

There are many different types of animals in the world. Many animals are quite similar to each other. Others are quite different. Animals can be classified based on their similarities.
Animal Kingdom can be split up into main groups, vertebrates (with a backbone) and invertebrates (without a backbone).

When you think of an animal, you usually think of something like a cat, a dog, a mouse, or a tiger. All told, around 800,000 species have been identified in the Animal Kingdom -- most of them in the Arthropod phylum.

In fact, some scientists believe that if we were to identify all species in the tropical rain forests the ranks of Arthropods would swell to over 10 million species! Most people do not normally think of a clam, a jellyfish, or an earthworm as an animal. Yet all of them belong to the kingdom of animals. The science of classifying organisms is called taxonomy.