ID: I have serious doubts that this one is "reef friendly", aiptasia?

[Treehrtsme]

Just got some cheap live rock from a (definitely reputable) lfs I have in a small tank hoping to revive old sand and rock. Guy gave me a bag of snail shells as a freebie. I've seen this growing out of maybe three or four of them so far and my guts telling me it's not something good. This is why I start out small. Can anyone tell me what this is and what I should do about it?

Thanks

 

[TokenReefer]

Toss the shell

 

[jabberwock]

Toss the shell

Yep, bye bye, and quickly.

 

[Dutch_Mill]

Why toss a perfectly fine shell? Just kill the aiptasia in one of the 1000 ways available and keep the shell?

Since you can easily remove the shell anything works from fresh water, drying it out or heating it up even.