What is the purple?

[bkushy]

can anyone tell me what this purple growth is?

 

[Sniperhank]

That is a sponge. Harmless filter feeder.

 

[bkushy]

I found the same thing growing on a rock. Is it certain type of sponge. I have pineapples all over the place. Curious what these would be called. Thanks for the info.