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.  When the animal retracts, the clausilium is pulled backward and it
closes off the interior of the shell much like an operculum.  Many species
have a lunella about 3/4 whorl back. This is a series (sometimes just one)
of 'tooth-like' lamellae on the inside of the shell.  These lamellae lock
the clausilium plate in place.  Very effective.

I can't remember the earliest known record, but the group was well
diversified by the Miocene throughout much of Eurasia.  There are basically
two main groups, although they are split up further.  The Nenininae (check
spelling) occurs in south, east, and southeast Asia and South America.
There are a few outliers in the Greater Antilles and elsewhere.  The
Clausilinae (again check spelling) occurs from Central Asia westward
through Europe.  This is a HUGE group.

I've heard that two European researchers are putting together a catalog of
the Clausiliidae of the world.  A welcome contribution hopefully out in the
next year or two.

OK, enough fun.  Got to work.  Kurt


At 08:12 AM 7/9/99 -0400, you wrote:
>>2. Why is the operculum of the Door snail (Land) called the
>>Clausilium?
>
>In Latin claustrum means door, or barrier. Incidentally, a clausilium is not
>exactly an operculum, since the snail does not carry it on its foot.
>Clausilium is a part of the shell.
>
>A.
>