Snails anatomy

The body:
anatomie de l'escargot

The body of a snail consists of foot (sole), a
head and a coiled visceral mass that is located
in the shell. Movement takes place by means of
expanding and extracting muscles in the foot.

This is clearly visible when you place a snail on a
glass surface, and look from below.

Mucus glands located in the anterior(front)part
of the foot secrete mucus. There are also mucus
glands on the rest of the body protecting the
snail against loss of water.

Two pairs of tentacles are placed on the head.
The upper pair bears the eyes. The shell is secreted by a thick fold of skin,called the mantle.
The shell is connected to the body throug a strong muscle which is attached to the
columella.It has branches to the head and tentacles.Contracting this muscle enables the snail to withdraw in its shell.
Inside the shell it forms the mantle cavity,which holds the heart,kidney and lung.

Snails living on the land are uricotelic,this means that to preserve water they excrete almost solid uric acid. Snails living in the water excrete ammonia, and are not uricotelic.

The radula:

The mouth has a tongue called radula.In the top of the mouth is a hard ridge and
food is being mashed between the radula and this ridge.

Le fonctionnement de la radula1: Rasp Tongue (Radula)
2: Radula Toothlets
3: Gristle Core
4: Radula is extended
5: Toothlets are withdrawn
6: Food is swallowed.

Image: "Encyclopedia of nature", Munich, 2000

The reptation:

la reptation Snails and slugs move by contracting and relaxing muscles in the foot. There are two sets of muscle fibers,each performs a different task. When moving forward one set contracts pulling the snail from the front and pushing it off toward the back.At the same time the second set pulls the outer surface of the sole forward. Both halves can move seperatly, creating a sort of locomotion called reptation.
Source: Arno Brosi

Glands produce mucus which allows snails to move over rough or sharp material and crawl on vertical surfaces. It's also used for protection and navigation.Snail trails are broken while slug trails are continious.