Zoa polyp or something else?

[Trestlew]

I got this Zoa frag from my LFS about a month ago. It's been doing fine but over the last week I noticed this section on the left with long arms growing. This was my first Zoa and first coral or any kind so please excuse me if this is a dumb question. I did dip the frag when I got it but I know that's not always 100% certain. Considering the other polyps are retreating from these arms I was worried. Should I be worried?

 

[Fishbro]

That’s an Aptasia. Bad pest anemone, remove it using Kalk paste or lemon juice squirted directly into its mouth, peppermint shrimp or bergia nudibranches. Also there’s Aptasia X and F Aptasia as well as a few other chemical things to remove it. Just remove it fast before it spreads.

 

[Fink]

one of my LFS is overrun with Aptasia, and it looks very similar to that. I'm no expert though. Hopefully some of the super smart reefers can give you a definitive answer.

Edit: a smart person was answering as i was typing this...