Barnacle Thing? - Pest or Guest?

I was looking at my tank and noticed this thing that looked like a barnacle with a hole in the middle of it. A few seconds later several little tentacles came out quickly and then went back in. It repeated this every few seconds like it was filter feeding or something. I don't really know what it is and any identification would be really helpful and also an answer on if it is harmful or if I can keep it in the tank.

 

Indo Pacific Hitch Hikers

Image is a bit blurred so I can not say for sure.

 

Not sure it's a barnacle. Does it move? Does anything come out of the hole in the top? The first thing that came to my mind was some type of limpet.

 

As far as I've seen it doesn't move and don't think it is a mobile creature. More than once I've seen several little clear but white dotted, almost feather-like, tentacles come out and quickly go back in, repeatedly every few seconds. It only does this when the lights are on. It seems to me like it is filter feeding or something??? And if it helps, i also know that it is attached to a patch of brown and white coral that also has short tentacles. Thanks for the replies... they have given me a little bit of a clearer understanding.

 

Well then now I'm leaning towards barnacle.

 

If it is a barnacle, is it harmful and should i get rid of it or can i keep it in the tank?

 

They're good, just filter feeders.

 

Actually, that looks like a keyhole limpet, and it may be eating your polyps. However, if you're seeing its gills poking out of the hole, it's could be a barnacle, as mentioned. Keep an eye on it...if your coral seems like it isn't doing well, remove it.

 

Your description sounds like a barnacle and they are safe.

 

Your description sounds exactly like a barnacle, but the pic looks exactly like one of the keyhole limpets that occasionally feed on corals. If it stays in the same place, it's a barnacle, and isn't hurting anything. If it moves at all, it's a limpet and probably one that you'll want to remove. Placement looks suspicious to me!

Cheers,



Don