Jan 12, 2014 #1 Edward2788 Aquarium Advice Apprentice Joined Aug 23, 2013 Messages 43 There's a few of these on the live rock
Jan 12, 2014 #2 fort384 Dividing by 0 Site Team Joined Nov 23, 2008 Messages 13,931 Location Illinois Appears to be pineapple sponges. They are harmless and come and go.