+1 for majanos
If you have some blunt tweezers, you can try to pop them off the rock. They are much more substantial than aiptasia and shrink down to a still fairly sizable and tough barrel shape. Try gripping that with tweezers as close to the base as possible and work them off the rock. Even if that fails, I've not found them to be as aggressive in reproduction by pedal laceration as aiptasia, so you're not going to create 4 new pests by trying.
When I've had majanos previously as hitchhikers or as surprise volunteers, I've been able to remove them this way rather than having to resort to chemical means. I'm not aware of anything that eats them, either.