small feather duster. Nothing to worry about at all. I have has tons in my tanks. Eventually, they will either just die off if you run a lower nutrient system or they become feed for fish like a wrasse or a copper band butterfly. Again, nothing to worry about.
As an aside, how old is your tank? It appears to be fairly new, older perhaps than the 4 weeks you had the zoas in your tank?
As an aside, how old is your tank? It appears to be fairly new, older perhaps than the 4 weeks you had the zoas in your tank?