Kurt,

>Just as an addition to the message below.  As stated, the clausilium is not
>homologous to an operculum.  However, it acts in much the same way.  It
>consists of a plate (the "pseudo-operculum") with a spiraled pedicle which
>extends upward and is embedded in and attached to the soft tissue of the
>animal.

The "spiraled pedicle" attaches to the columella, not to the snail. Otherwise,
the snail would be trapped in its own shell as the clausilium stays in the
shell when the snail is out. The attachment point can be seen by breaking open
a clausiliid shell above the aperture. The clausilium is somewhat like a door
hinged from the top, the hinge being the "spiraled pedicle". When the snail is
coming out I believe it simply pushes the clausilium out of the way. And as
the snail is withdrawing, the clausilium falls back down. It is fun to watch
this happen by holding a live Albinaria upside down under a dissecting scope &
gently poking the snail to force it to go in its shell.

A.