Apex: The point of the shell where the whorl is smallest; also the part of the shell that developed first.
Suture: the spiralled depression on the shell which separates the whorls.
Whorl: A whorl is a 360o rotation of the shell.
Body Whorl: The largest and most recently formed whorl.
Spire: Consists of all the whorls except for the body whorl.
Aperture: The large opening of the shell, through which the head and foot can be retracted.
Operculum: A firm disk, found on the posterior dorsal surface, that when retracted seals off the shells entrance.
Note: Above information from Ruppert (2004).