Today, we will begin to talk about the other large group of animals called invertebrates. An invertebrate is an animal without a backbone or a skeleton inside its body. Some invertebrates have a soft body, while others have a hard outside covering. Scientists classify invertebrates from simple to complex, according to characteristics of the body parts. The simplest of the groups is the sponges.
Sponges live in the ocean.
The next group is the hollow-bodied animals. This group includes jellyfish, hydra and coral. The animals live in the water, they have a hollow center, and only one opening. The third group is the worms. They are soft-bodied animals that live on land or in water.