Whar are these things under a coral frag?

[Midnitecloud]

So I picked up this frag to clean off the hair algae and these were under it. What are they and should I kill them?

 

[JCOLE]

It just looks like pineapple sponges to me. If so, then no worries as they are good filter feeders.

 

[Zos4me]

Yep i have them on my rock as well

 

[GThompson]

I agree on pineapple sponge. They like darker areas. But as mentioned, they are good

 

[Gonzo74]

Pineapple sponge. Let them be, they are good.