Caulerpa nummularia?

[yardartist]

This sprouted about two weeks ago and several other groups are starting around the tank. Anyone able to ID and say how aggressive it is? Runners about an inch long in the photo. Thanks,

Attached files /attachments/sites/default/files/Caulerpa_nummularia.jpg

 

[A_Lee]

I had C. racemosa, which looks similar (not the exact same though) to what you have pictured. It grew like mad. I could never get rid of it in my last tank, as runners always sprouted from crevices and holes. Very aggressive grower ... it actually just about grew into some stalks of pulsing xenia I had nearby. It eventually came to pruning back 2-3 times a week, which is a PITA. It's actually part of the reason I tore down my last reef tank.
I'd try and get rid/control of it asap. Maybe a small tang. Though, I put a small Z. veliferum into my last reef tank, and it didn't touch the Caulerpa Take that for what it is worth ... maybe the tang I got was just ... weird

 

[GreshamH]

Could be a racemosa as suggested. It also does the caps like that.