New hitchhiker

[Gtojr]

I just had this guy come in on a frag. with a couple others like him, he hopped off and made himself at home.  Assuming it is a form of anemone but wanted input on if he is invasive of if I should keep him around.

[WV Reefer]

2 minutes ago, Gtojr said:

I just had this guy come in on a frag. with a couple others like him, he hopped off and made himself at home.  Assuming it is a form of anemone but wanted input on if he is invasive of if I should keep him around.

Aiptasia. Big time pest. 

[Squid_reef]

Aiptasia indeed. 
100% Invasive
 

It's best to try to get rid of them as soon as you spot one to control the population - be aware that if you poke one it will spawn and you'll probably end up with many others in a week.
They tend to be a mare to get rid of because of this, also they withdraw quite easily into live rocks when feeling in danger making it even harder.
 

The best you can do is to quarantine the rock where the Aipstasia is and try to take it off - then do a quick dip/clean before you place it back in your main tank.
 

You can use injection (Aipstasia-X or Kalkwasser) it will kill it -  but you will probably have them spawning beforehand anyway so it's not 100% effective. 
 

If it's getting out of control you can also get Berghia Nudibranch, they exclusively eat Aipstatia - The downside is that once they have eaten all of them they would die from starvation.
 

Best of luck.