What are they?

[saline]

Noticed a few of these when I was moving around some rock about two months ago.They seemed to go away. In the last week they popped up again. Now they're everywhere.On the undersides of rock and pretty much all areas.They are prickley as I inadvertantly put my hand on one while cleaning.Everything in the tank is doing great! Any ideas? Thanks in advance.....J

 

[Bifferwine]

Those are pineapple sponges. Also called scypha or q-tip sponges. They are harmless, and filter feeders, so the more food you have floating around in your water, the more the population will take off. You don't need to worry about them, but can pluck them off if they bug you.

 

[saline]

Thanks Biff, and I thought that might be them. Makes sense that I'm seeing more of them now because I just switched to Brightwells Reef Snow, which everything seems to like, and be going nuts over..Thanks again....J