Weird stuff growing on my rocks, what are these?!

[elekamit]

Any idea what this is?
I found some growing on my rocks, and today when I looked behind my rockwork in the shade I found a whole fleet of them:

http://www.reef-center-host.com/pix/albums/userpics/10059/P1000573.JPG

http://www.reef-center-host.com/pix/albums/userpics/10059/P1000578.JPG

[stubby 58]

pineapple sponge's - good for tank . stubby

[skippy2]

those are Scypha sponges. also known as pineapple sponges. Good filter feeders.