Thought it was a limpet but then...?

[acabgd]

Rarely do I find something in my thank that I cannot identify, although it does happen from time to time. This one really got me baffled - saw it this morning at the center of my tank, on the bottom. Size is about a quarter. It didn't move obviously.

 

[Crabs McJones]

Did you have any turbo snails or larger snails? it looks like a snails operculum

 

[acabgd]

Indeed. After I read your message, looked around and found a giant snail that apparently kicked the bucket. Never knew it could get that big and thick.
Thanks!