Looks like vermetid snail or tunicate but thinking vermetid. You can take an old credit card and remove/discard afterwards. hey build up their tube so they can spit their mucus into the flow of water, yet without letting the mucus go. This mucus then picks up small pieces of food, which they then eat with the mucus. If you start seeing them in your tank don’t let them go untouched. They will build a large population and annoy your expensive corals you’ve worked so hard to keep happy.