What could it be? I am pretty sure it is harmless.
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How long did they last? I have had a couple colonies for about 6 weeks now.Got those. ID I got from others was a tunicate. Mine unfortunately didn't last.
I'd like to say a month or so. It may have been bothered by the cup corals on either side of it, and my green RFA eventually moved right on top of it's spot (can't remember if before or after it disappeared). Always the possibility of some evil presence in my gulf rock that comes out at night when I'm not in the office!How long did they last? I have had a couple colonies for about 6 weeks now.

