The one that got away. It looks like some critters tooth would still fit in that hole. Makes me wonder if the guard was malleable while inside the belemnite?
I wonder if it could be fungal? There is a fungus (or group of them) which attacks abalone. It severely weakens the adductor muscle, causes swelling and shell damage similar to the damage on that Nautilus shell, the inner nacreous layer gets dark chocolate brown lesions too. It has a pretty high mortality rate. (See REFRESH)
Wow, that last one looks fungal -- any idea what the actual cause of death was?
Edit: Hah, you got there before me. It sure does look like a fungus, though, doesn't it? Especially the thickening with the brown lesions...I've seen that in gastropods before.
Pathologies or broken shell repair on a specimen of Girtyoceras sp. from the Mississippian Chainman Shale (Asbian). Top: broken shell repair. Middle: Bite mark or parasite? on venter. Bottom: lateral view of specimen (26mm dia.).
The thing looked a little too fragile after my initial brushing so I just left it alone. The matrix that forms the internal mold is a soft phosphatic material, and the shell is attached to that, a little more cleaning could fowl the whole thing up. I'm afraid to put Vinac on because I don't find very many with the shell preserved so well, and the preservative may cover up some fine details.
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