David,

Not all opercula reveal the direction of growth.  Although some grow
spirally, others do so concentrically. Those of the latter type cannot be
analyzed to infer the orientation of the animal which secreted them.

Harry


At 06:50 PM 1/3/2005, you wrote:
> >  >    Now get to the basic question: IS there handedness at all in
> >  >fish, bugs, birds?
>
>Organisms that are active enough to have detectable preferences often show
>a preference for one side or another in doing things, similar to humans
>being left or right handed.  Almost all of the carbon-based molecules in
>organisms show a distinct "handedness".  However, mollusks are relatively
>unusual in having many kinds that are normally distinctly
>asymmetric.  Many forminifera have snail-like coiled shells; these can be
>sinstral or dextral, too.  Bivalves with hinge teeth typically have
>different teeth in the left and the right, and there are rare individuals
>with the teeth swapped around, analagous to sinistrality in snails, except
>that some groups of teeth may swap while the others are normal.
>
> >  >     In shells, it is the shell that is sinistral. How does that
> >  >affect the critter in it?
> >  >    Q Man
>
> >  Sinistral shells don't affect the critter, as the critter MAKES the
> >  shell. A reversed animal will make a reversed shell. So the entire
> >  animal and shell are exact mirror-images of a normal specimen.
>
>This includes the coiling direction of the operculum.  Thus, a fossil
>snail that preserves the operculum can be easily identified as sinistral
>or dextral.  Without the operculum, known close living relatives, or
>distinctive shell features (such as a siphonal canal), it is difficult to
>tell whether a specimen is orthostrophic, hyperstrophic, dextral, or
>sinistral.  This particularly arises for certain Paleozoic to early
>Mesozoic extinct snails (or maybe not even true snails!).
>
>     Dr. David Campbell
>     Old Seashells
>     University of Alabama
>     Biodiversity & Systematics
>     Dept. Biological Sciences
>     Box 870345
>     Tuscaloosa, AL  35487-0345 USA
>     [log in to unmask]

Harry G. Lee
Suite 500
1801 Barrs St.
Jacksonville, FL 32204
USA
Voice: 904-384-6419
Fax: 904-388-6750
<[log in to unmask]>
Visit the Jacksonville Shell Club Home Page at:
www.jaxshells.org

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