more than likely a peanut worm or a sessile snail most things that are in tubes are filter feeders and are harmless.
as far as the apistia you can get kalkwasser and mox with water thin enough to be sucked up into a syringe and inject it into the anemone to kill it. there is also a product called joes juice that works simliar. You can get needles from the vets office just get recipt for the needle so that it cant be said it was drug parafin.
Just make sure there are what you think they are there are many things that look similar one can be good the other bad.
Mike