Mushroom? Maybe?

[Knight]

I was clearing a very old piece of rock of some vermetid snails and stumbled upon this guy in the middle if three tubes. When I glue him to this plug he was grey and maybe 1/8 inch across. Now he is about the size of a dime and maroonish on the outside, with blue dots, the center is white, with maybe a mouth. Bumpy textured all over, and rather pretty, but no idea what he is. Thanks for your responses.

 

[Jbissell1289]

Looks like a shroom but I could be wrong.

 

[LaxFrags]

I have no idea if it’s even possible but the first picture makes it look like a small Maximus clam of some sort (I think that’s the name of it?).