David,

I do not know of specific works but can offer the following that I gleaned from research on an exhibit I produced several years ago on forces that injure mollusks in their lives and  the results therein. My exhibit focused on mollusks that had lived through attacks but revealed other facts including the following.   

Sulphur sponges, Cleonia sp. are a major force in the degradation of dead shells. They absorb the calcium carbonate for their own skeletons, ultimately absorbing the entire shell. A partially absorbed shell appears to be as Swiss cheese - totally riddled with holes and galleries. Cleonia cannot survive buried in the ocean bottom. That part of a shell buried in the bottom  is protected from the sponge. If the shell is dislodged from its place in the bottom by shifting currents and subsequently washed ashore those parts that are partially absorbed break away easily (separating along the dotted line comes to mind) leaving the unabsorbed portion. That is one way that one finds large gastropods beautifully split down the spire revealing the inner spire structure. The question is "how can something so fragile get split like that without destroying the spire?" This is but one example of the effects of Cleonia. I have shells missing syphonal canal, dorsum, spire only, etc. It depends on what part of the shell was buried in the bottom. The clue that a sponge was involved is on the break surface with the galleries of holes.

Cleonia also absorbs the calcium carbonate of living mollusks that do not bury themselves in the bottom often wearing down their vitality in the process. They are a major contributing factor the the scarcity of complete Cassis madagascariensis along North Carolina shores. Not to mention that the dorsum is the most delicate part of the shell thus very vulnerable to damage by surf action as they come ashore. Having perforations in that part of the shell does not help matters. Thus even a very fresh dead example of this shell may have already begun degradation when the animal was alive.  

Stone crabs leave characteristic remains of mollusk shells. They pick away at the shell starting with the lip of the shell and progress up the spire to reach the animal as it retreats, and ultimately its organs. I have examples of shells eaten by this animal including Neveritia duplicatus. The shells appear to be very fresh dead. A crude canal has been chipped out of the shell following the thinnest part of the shell up the spire. In the moon snail that is the top of the spire.

John Timmerman

Wilmington, North Carolina

USA

-------------- Original message from David Kirsh <[log in to unmask]>: --------------


> Does anyone know whether there has been much study of the common ways
> that shells are eroded or broken?
>
> I've noticed that I can be walking on an Atlantic beach with someone
> who doesn't seriously collect and they'll pick up a (to them)
> attractive fragment and I'll know from a small sliver what it is. (But
> I might not be able to explain how I know). How many ways are there for
> Neverita duplicata to be eroded and broken and sliced by waves and
> other environmental factors? It seems like there are quite a few
> "forms." It can be challenging to identify certain atypical fragments
> or eroded shells of less familiar species.
>
> Some shells are known mainly in their incomplete state. For in stance,
> they might be invariably "decapitated" by the time they're adult. In
> such cases, we're unfamiliar with what they would look like intact.
> Just yesterday, I found a young Truncatella with its protoconch intact
> and I'm hoping to post an image of that soon.
>
> David Kirsh
> Durham, NC
>
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