<a href=showthread.php?s=&postid=15314633#post15314633 target=_blank>Originally posted</a> by Yogre
Just to add to what figuerres said, these animals are, according to Richard's website an aiptasia family anemone. The difference seems to be that the Caribbean species does not aggressively spread like the Indo-Pacific species do.
I had 3 that hitchhiked in on my rock. One was in a sponge that died, so I pitched it. One disappeared, I suspect my peppermint shrimp population ate it. The third has gotten kinda big, I may Joe's Juice him 'cuz I don't need the threat to my fish.
At the end of the day, I think you have to decide if you like 'em or not, but based on what I and others like figuerres have seen, I don't think they're a huge threat to your tank like the Indo aiptasia are.