Critter ID Help, Tentacles

[Flare]

Hello all, my reef system has been running for about two months, current stocking is a clown fish, diamond Goby, Royal Gramma, and pajama cardinal. I had a small clown fish and Bangai cardinal not make it, but never saw their corpses.
I see a couple of these critters around my rockwork next to corals, I worry they irritate my corals, they react to water movement, I tried to touch with tweezers and they completely hide away, what are these? Thanks in advance.

 

[Crabs McJones]

Looks like aiptasia anemones unfortunately

 

[jabberwock]

What is the source of the rock?

 

[Tahoe61]

Aiptasia unfortunately. Deal with them now or pay the price later.

 

[Reef Breeder 2013]

Yeah, I could say they're aiptasia. People generally don't like them because they harm corals, but my Aiptasia stay on the surface so they can pick up the flakes that my fish don't eat. If you'd rather not risk them killing your corals, you could get some peppermint shrimp.