Kurt,

The best (and only) explanation of the structure & function of the clausilium
of the Clausiliidae that I could find is in Kerney & Cameron's "A Field Guide
to the Land Snails of Britain & North-West Europe". This is what they say:
"...the upper attenuated end of [the clausilium] is fixed to the columella.
When the animal is crawling the clausilium is pushed elastically out of the
way into the groove between the columellar & subcolumellar lamellae, but on
retraction [of the snail] the expanded end springs out against the palate &
blocks entry into the shell." You really need to break open a shell to fully
understand how this happens. I examined one of my broken Albinaria shells. If
I had had a digital camera I would have taken pictures for all to see. I
suppose the clausilium originated as a columellar tooth. It starts from the
columella about a whole turn behind the aperture as a stiff but flexible
ribbon, spirals around the columella then expands into the clausilium proper.
When I gently pushed on the clausilium with a needle coming from the inside of
the shell (just as the snail would have done), it moved towards the dorsal
side of the shell, opening the entrance. Note that the clausilium always
remains inside the shell.

Hope this helps.

A.
------------------------------------------------------------------
On Fri Jul 09 10:13:31 1999,
"Kurt Auffenberg" <[log in to unmask]> wrote:
>>
>>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.
>
>I'm having trouble visualizing this.  Has anyone done any work on from
>where in the shell the clausilium is generated?  Is it some weird part of
>the columella?  Is it actually attached to the columella by shelly material
>or connective tissue?
>
>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.
>
>Where does it get pushed to?  Outside the shell or does it remain inside
>out of the way someplace?  I've collected a bunch in Pakistan but didn't
>observe them alive for long.  I dissected out a clausilium from a species
>we described from there a few years back.  I didn't pay any attention to
>where it attached at the top of the pedicle.
>
>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.
>
>Thanks for the info!!!  Kurt
>>
>>A.
>>
>