Many think snails are incredible but the majority of us just think their kinda disgusting. But when you start looking at their anatomy you cant' say they are not unique.
The most notable difference between a snail and slug is a slug has better house that is to say their shells. The shell varies tremendously on what type of snail it belongs to. Sometimes their flat while others are round. Some of them even spiral though they do serve some protection against hunters most hunters can pretty easily break through the shell. Instead they mostly serve as shelter and also a place to put the majority of their major organs. The primary ingredient to the shell is calcium and a snail must consume a lot of it.
The shell of a snail is even more important for the land snails that we often visualize when we think of snails. Some snails even live in the desert. They need the shell in order to protect themselves from the dryness of the outside world where their wet bodies would shrivel up and die. For water snails it is less important.
The eyes of a snail are on the end of tentacles. Sometimes they have two sets of tentacles but only one set up eyes (the eyes are always on the longer set of tentacles). their brain is pretty small. But their smarter than we originally thought they were. Were especially impressed with their associative thinking. That means basing their thoughts on past experiences.
The snail doesn't have a lung like you and I do but they do need air to breathe and they have a sack of blood vessels which performs the same function of our lungs. But they only have one of these sacks. They breathe through a respiratory gland on the upper part of their body that's because their mouth is always on the ground as it's on the underside of their head.
They have a "foot" that is a tougher more leathery version of the skin on their underside. But only the rear part of their body has this tougher skin. That's because the upper under-body is too busy producing mucus so it produces enough to slide over and also gives the lower part of the body extra protection. This might seem like a lot of mucus but its important to remember that they move slowly so they have plenty of time.