Help ID this thing on my coral?

[octoreefer]

I noticed these white things growing on the bottom side of my coral. Coral dip doesn't do anything to them. What should I do? Are they bad?

 

[AlyciaMarie]

Pineapple Sponge. It's a harmless filter-feeder, but it can be easily scraped off if you don't like the way it looks in your tank.