We just started putting corals and forgot what it was.....

[Vlrm23]

The guy at the lfs just said it was poisonous and to give it a lot of space and would like to know what it is to learn more about it..... Thanks!

 

[mr_X]

I can't tell from the picture, but I'm going to take a guess from the description and say it's an encrusting hydnophora. Not poisonous, but it has sweeper tentacles that it extends at night if it senses corals close by. It will sting the corals to death eventually. I have one in my tank actually.
look like it?

 

[Vlrm23]

Yeah, pretty much. Thanks for all your help!