Commonly referred to as a Ball Anemone. Technically a coralimorph. IME they won't be around for long, although others have had them reproduce too much. Can they sting corals? probably
I have clear ones that stay in low light but these ones are in high light and they are multiplying not rapidly but fast enough to notice them taking over areas on the rock. I never had ones that have green fluorescent spots or that grew in high light. So I'm debating killing them, they just look so cool under the blues that its a hard decision lol.