Borlumastus yildirimi from Turkey
The aperture is the opening of the shell, whereas the apex is the very top of the shell. The last whorl is called the body whorl, because when the snail's foot is out, most of the rest of its body will be in there. The body whorl is also the ultimate whorl and the one above it is the penultimate and the one above that is the antepenultimate whorl. The rest of the shell above the last whorl is referred to as the spire. Suture is the line that forms along any two overlapping whorls.
The shell a snail builds before it is born is the protoconch and the shell it builds afterwards is the teleoconch. There is usually a break between the protoconch and the teleoconch across which the microsculpture of the shell may change. The sharp radial break visible in the picture of Zonites casius (above, left; white arrow) marks the point where the protoconch (above, right; blue outline) ends and the teleoconch begins. The picture below shows a shell of Anguispira fergusoni where the end of the protoconch is marked by a change in the microsculpture (arrow).
Anguispira fergusoni from Maryland
Snail shell terminology 2
Snail shell terminology 3
Snail shell terminology 4