Zoologists divide animals into about 30groups.First,they divide them by whether they have a backbone.Animals that have a backbone are called vertebrates.Animals that do not have a backbone are called invertebrates.
The biggest and best known animals are vertebrates.Mammals,birds,reptiles,amphibians,and fish are vertebrates.You are a vertebrate.Your backbone is also called your spine.There are about 40,000species of vertebrates.
There are far more species of invertebrates.Even though you can probably think of many vertebrates,the many kinds of invertebrates greatly outnumber vertebrates.Almost all invertebrates are small animals.Insects,spiders,mollusks,and worms are all invertebrates.The biggest invertebrate is the giant squid.It can be up to 60feet (18meters)long.
Cold Blooded and Warm Blooded Animals