Barnacle. To go or not to go?

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I've got a barnacle on a newly aquired clam about 3/4" round and don't know if I should try to remove it or how if I should. It is attached near the top of the clam on the outside of its shell and it is fishing out a lot of stringy lines sliming up some nearby corals. Its seems to annoy them but not really causing any damage that I can tell.

Are these bad and if so, how do you kill/get rid of it?