>I have seen live-collected Buccinid shells from Aleutian waters that were
>worn through, where the animal presumably dragged the shell on the sharp,
>black volcanic sand substrate as it moved around.  The dorsal periostracum
>was intact on these shells, so I don't think that they had been tumbled by
>wave action.

Wear in a particular spot can only occur over time. In gastropods
with a patch of pearietal area worn, you'll find that generally the
specimen was an adult who had stopped growing some time beforehand,
so that the shell was no longer being rotated about its axis as it
grew. Thus the one spot sat on the operculum for long enough to wear
the shell. Note that inoperculate shells do not show this type of
wear. Buccinids (including melongenines and fasciolariines) and
ranellids are perhaps the most frequent examples of such wear.

>I have also wondered about cold water species seeming to have
>shells that appeared to be partially disolved; thinned almost to the point
>of not being intact, as if some acidic solution had come in contact with the
>shell.  These were also live-collected, with almost no periostracum.

In very cold water calcium carbonate is more soluble than in warm
water; therefore shells from these areas tend to exhibit corrosion
(this is not erosion) problems, often severe. This also happens in
deep (and so cold) waters. Which is why forms living there have
evolved periostracum to resist this.

Go deep (and cold) enough into the abyssal region and you reach what
is called the carbonate compensation depth, where cold and pressure
combine to dissolve all carbonate... below this depth no forams,
coccoliths or pteropod shells accumulate on the bottom, as they
dissolve.
--
Andrew Grebneff
Dunedin
New Zealand
Fossil preparator
Seashell, Macintosh, VW/Toyota van nut
‚ Opinions stated are mine, not those of Otago University
"There is water at the bottom of the ocean"  - Talking Heads

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