First ever post in R2R so sorry for any formatting issues. I’ve tried other threads and Facebook pages to try and figure out what these things are with no luck. Everyone tells me it’s a stomatella, or some sort of limpet, or algae growth, but I can say with 100% certainty that it’s none of those. It is living, it doesn’t move, and it has this super hard outer shell. I picked them off and saw that they had meaty insides, kinda like a mussel... When I picked them off I saw no damage to the hammer’s skeleton so I don’t think they’re dangerous to coral, but I could be wrong since I don’t know what they are lol. This picture was taken a while back and recently I found one that was about the size of a quarter on the underside of the frag plate. The ones in the image are about pea size. Hopefully I can find some answers here because I would like to know what’s gotten into my tank. Thanks in advance!