Friend or Foe, any ideas?

[threebuoys]

I found several masses like this on a rock today. Any ideas? It is only a couple of days old at most, or at least at this size.

 

[Jseimo]

Kinda both. It’s a type of sponge. Great filtration, problem is they can grow out of hand sometimes and annoy corals. But they’re easy to deal with if you wish to get rid of them