Look like palys and they definitely spread fast. I was given a free frag of 2 heads when I bought some frags a few months ago. In that time, my rastas went from 1 to 8, the duncans 1 to 6, and the palys... 2 to I can't even count. I ended up moving the rocks they're overrunning away from other rocks to avoid a dedicated paly tank. They'll be going in my sump when I upgrade lol