Where does a snail get its shell?
Note: I copied this answer directly from:
http://rochester.kidsoutandabout.com/main-columns/nature/snailshells.html
Snails are hatched from eggs. When they hatch, they eat most of
the shell, but a small part of it stays with them and that is the
beginning of their shell. As the snail grows, so does its shell --
in a spiral shape. New shell is added at the opening of the shell.
In the center of the spiral is the part of the shell that the snail
began life with. The shell is made from several layers. The thin
outer layer is made from an organic substance known as conchiolin.
The thicker layer underneath is formed from three layers of
crystalline calcium carbonate, similar to the chicken egg of which
you may be more familiar. The color of the shell depends on the
types of food the snail is eating and also the type of snail.