Many shells have a dormant stage from time to time, either by the cold water or lack of food supply. That is the time when other marine life can attach. I've seen it from time to time, but it is not common in cowries. Helmets and Tritons can usually clean or knock anything off with their powerful radula sheath. It can reach any part of the shell. " Observations in an aquarium for over quite a few years." I have slides of a Charonia variegata cleaning itself.

Bob

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