what is this?

I don't think its a mushroom as it like light but not alot of wter flow it was on a rock with some green star polups in a location that the star polups liked as that is why I got that rock and frag. It looked like it had a bunch of small feet on its bottom but now there is none of them there looks like there is only a single foot now. The lfs guy that sold me the rock gave this guy a squeze before putting the rock in the bag. He shruged his sholders after words. By the way the lfs was on the coast.
As I said it kind of looks like it is scone shaped.
Bill