Is this a pest?

found these things about a week ago on my corals, i haven't touched them but i'm a little curious/worried as to what they are. Can somebody tell me what these are and if they can harm my corals/tank? If they can, whats the best way to get rid of them?

theres one my zoas, favites coral, and mushroom frag. here are the pics









sorry about bad quality, taken with iphone.