aiptasia,pest anemone,- kill it. joes juice, kalk, lemon juice, or boiling water -- injected into its mouth. They spread like wildfire if not killed quickly.
It's fine to do in the tank. There are probably more, keep searching and killing as you find them. I go on an aiptasia hunt every Sunday and always find new little ones zap. I prefer Joes Juice myself. Only need be careful if using near a good anemone such as a sebae, gbta.....
yea deffinately get rid of it..i use aptasia-ex or somethin like that...you can get it at any LFS...they might be cool lookin sometimes but if you wait to long to kill them they will spread everywhere...i had 2 in my little 10 gallon...now there r about 10 within 2 weeks..and the 2 i started with are big now...there oral discs are as big if not bigger than a quarter...they eat anything that flows across there tenticals and you can see the food inside them lol..interesting but annoying..thats all they are lol