Pics of the mouth would help - I don't know if it's an Edwardsia species (it could be; there are dozens of species in the genus and I'm not familiar with all of them yet), but I think it's quite likely at least from the same family, Edwardsiidae.
These aren't Tube Anemones - those are Ceriantharians, rather than true anemones, and they have two, distinct whorls of tentacles while true anemones have one. Edwardsiid anemones are true anemones sometimes called Worm Anemones; they're known for their long, wormlike body-shape and for most species living burrowed in substrate or rock.
Honestly, Worm Nems are pretty rare hitchhikers and pretty neat; I haven't heard of them reproducing in our tanks yet (though I haven't looked at if they've been cultured in a lab setting yet), and they tend to like to stay in one spot from what I've seen - so they should theoretically be fairly safe hitchhikers to keep. Not sure on the sting potency yet (again, these aren't common, so I haven't looked too deeply at them yet).