I think they are also called lightbulb anemones. That guys tenticles will swell up a bit if you feed it. I had a bunch come on my live rock which also came from the Gulf. I heard they were colonial and would spread but mine have stayed pretty tame. I killed a lot of them by injecting them with boiling water so I could clear some landscape for corals. I still have 3 huge ones in a corner area and they don’t seem to bother anything or want to split or spread.