What what are invertebrate groups?
Just a fraction of all known species-fewer than 50,000 are vertebrates, such as mammals, reptiles, anphibians and fish. The rest are inverterbrates appeared in the Earth’s oceans more than 650 million years ago. Today most inveterbrates still live in oceans, but they can be found in almost every habitat worldwide. Inveterbrates, unlike veterbrates have no backbone. In fact, they have no bones at all. Inveterbrate bodies are usually supported by some kind of skeleton. Spiders, Crustacean and insects are the main phylum of Inveterbrate.