Anyone know what this is?

[SWstart]

Bought a new tank and had a array of coral in it before I bought it, had a few pieces left. After refilling the tank and setting the rocks the next day with the new light this little guy came out. We think it’s a anemone but I’m not sure. Anyone know if this things dangerous to my coral, fish, or snails?

 

[Sharkbait19]

Looks like a closed up mushroom, but it’s hard to tell.