The friendliest place on the web for anyone with an interest in aquariums or fish keeping!
If you have answers, please help by responding to the unanswered posts.
Agreed. It's aiptasia. Not desirable at all. Trying to remove them by pulling them or plucking them from the tank can cause them to spread. Many people have used Joe's Juice injections to rid their tanks of them.
There are other methods as well. Like injecting it with kalk or boiling water, etc. Also, if they are small, sometimes peppermint shrimp can be used to get rid of them.