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. Flatworms and earthworms are examples of this group. The fourth group is called mollusks.
Mollusks have soft bodies, but some have a hard outer shell.
Some live on land and some live in water. Examples of this group are snails, clams, oysters, slugs, squids and octopus. The next group is the arthropods. These animals have an outside skeleton, jointed legs and segmented bodies. Three-fourths of all the animals are arthropods.