The snail tube is about the diameter of a pencil. The snail's operculum covering the shell's opening is visible. One of the interesting peculiarities of animal diversity is that within the huge group of insects, they really do not look all that different. Once you have really looked good at an insect, it is unlikely that you would ever confuse an adult insect with an adult animal of any other group. There is only one characteristic that separates snails from all other groups of mollusks, and that is that they undergo torsion.
Torsion is an internal twist that generally occurs late in the snail's larval life.
During torsion, the animal's viscera behind the head and above the foot rotates 180 degrees, bringing the anus to lie pretty much right above the head. Now, this process is bizarre in the extreme, and is probably related to the locomotion of the animal and the way it must carry its shell. By the way, torsion does not equal coiling. However, the point is that the only thing that absolutely defines snails is internal - and invisible to the casual observer. Furthermore, unlike the insects whose morphology is confined and defined by their exoskeleton, the snails have a notoriously variable shape.