Yep, it’s an aiptasia. They will sting other corals and reproduce. There are many ways to get rid of them. As mentioned above you can try to seal them in with superglue. I’ve never found that method to be 100% effective but it can work. Other options are to inject them with Aiptasia X, Joe’s Juice, or kalk paste (calcium hydroxide). Also injecting them with boiling water. You can also pull the rock out and scrub them off (make sure you get all of it and don’t leave any bits of tissue, as that can grow back - this can be difficult). I would watch some YouTube videos on how to do one of the first two methods.