Arrows point at the columella of Albinaria anatolica, a clausiliid land snail from southern Turkey.
The columella is the central axis inside a snail's shell around which the shell spirals. The columella forms from the innermost walls of the whorls. The columella is hollow. On the bottom of the shell, the columella may open to the outside as the umbilicus or, if the snail has determinate growth, it may be covered by the edge of the lip in the adult snail.
To be continued...
Snail shell terminology 1
Snail shell terminology 2
Snail shell terminology 3