>I touched on the idea of waves smashing shells coming into beaches.
>Water motion also contributes to specific wear on some shell species.
>
>Large, heavy Busycon such as Busycon carica and Busycon sinistrum
>frequently have a worn spot on the previous whorl adjacent to the
>aperture just outside the columella. Large examples of the species
>tend to role over with the aperture facing down. Wave action and
>currents shifting the shells back and forth or along the bottom
>presumably is the cause for the thinning and ultimately wearing
>through of the shell whorl. It is a process that begins quickly upon
>death of the animal thus finding an example without anyt of the wear
>is more the exception. I see the same wear to a less frequent extend
>on Busycotypus canaliculatus but have never observed it on
>Busycotypus spiratus, both much lighter and thinner species - even
>at full adulthood - which have a more evenly distrubuted center of
>gravity thus more likely to role than slide when moved by water.

I have seen this on living specimens (and live-collected ones) and
have deduced that it is wear caused by the shell resting on the
operculum of the moving animal. Fusitriton, Busycon, Penion,
Pleuroploca, Turbinella, Clinuropsis etc.

>Another water action wear occurs on certain bivalves with a tough
>hinge ligament. One is Dinocardium robustum. As the shell tumbles
>around the valves move back and forth producing a characteristic
>wear on each side of the hinge to the facing valves. This is not to
>be confused with drilling by moon snail or murex. It is most evident
>when finding both valves still attached cast up on the beach. The
>wear is flat as though the area was simply filed off rather than
>bowl shaped as a predator would make. It is also evident equally on
>each valve rather than the one one valve that a predator typically
>would leave.

This wear occurs in life also. In fact in some species it is not
uncommon to find one of the umbones worn right through.
--
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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