Snails and slugs are both part of the same class of creatures  | Learning English

Snails and slugs are both part of the same class of creatures called gastropods. Gastropod comes from the Greek words gastros (stomach) and podos (foot). If you've ever seen a snail in an aquarium eating as it moves slowly along the glass, you probably understand why “stomach foot" might be an appropriate name!
Most gastropods are aquaticcreatures. That means they live in water. Snails and slugs are the only gastropods that can also be found on land. The majority of snails and slugs, though, live in water.
The most obvious difference between snails and slugs is the fact that snails have shells. A snail's shell is like a home it carries around on its back. Slugs, on the other hand, have no shell. Otherwise, snails and slugs are remarkably similar.
Their only other differences are in habitat and behavior, but these differences are the result of the fact that snails have shells and slugs don't. Without those big shells to carry around, slugs can squeeze themselves into many different habitats that snails can't. For example, you may find slugs under loose bark on trees or stones and logs on the ground — places that snails could never go with their shells.
If you spend much time in a garden or the great outdoors, you may be more familiar with snails and slugs that live on land. As they move along, you've probably noticed that they often leave behind a slimy trail.
That slime is called mucus. Snails and slugs make mucus so that they can move on the ground. The mucus keeps their bodies from losing moisture to the dry soil beneath them. It also protects them from being cut by sharp objects in the soil.