>I have asked this question for some reasons but principally because I am
>wondering if AGE (not size) can have a negative influence (as in almost
>everything in Earth)  to the shells' composition (i.e. resistance), things
>like younger - strong calcium carbonate layers ; older - weaker calcium
>carbonate layers. Could be possible to have  a "age limit"  for a perfect
>quality shell  ? or older = bigger = better ?

It depends on the environment and the species.  Many species keep growing
indefinitely, although upon reaching maturity they grow more slowly because
they are putting energy into reproduction rather than growth.  Others have
a fixed adult size and stop growing larger at that point.  If the water is
corrosive (such as most fresh water), then older shells will often show
damage.  The juvenile shell of adult freshwater specimens is often damaged,
for example.  Also, the older the shell, the more chances it has to run
into a predator, bang into a rock, or otherwise damage itself.  A shell
that just reached adult size is likely to be more thin-shelled; older
shells will have had time to deposit more shell and thicken the thin parts.
In some species, very old specimens will have additional shell deposits
and other unusual features.


Dr. David Campbell
"Old Seashells"
Department of Geological Sciences
CB 3315 Mitchell Hall
University of North Carolina at Chapel Hill
Chapel Hill NC 27599-3315 USA
[log in to unmask], 919-962-0685, FAX 919-966-4519

"He had discovered an unknown bivalve, forming a new genus"-E. A. Poe, The
Gold Bug