What is this?

[JmeJReefer]

Looks to be aptaisia anemone.

couple of options to get rid of them...
1. Slush mixture of sea salt applied directly onto anemone via baster.
2. Aptaisai X chemical remover.
3. a squirt of boiling water on the site.
4. Peppermint shrimp (hit or miss)
5. Certain fish eat it
6. bergia nudibranch
7. cruise missile

the last one might cause a sandstorm...