What is this on my rock?

I have posted some crappy quality pictures before of this, but it has grown a bit and my wife got a much better camera for Christmas so I took some more. The general response I got before was that this might be a sponge. I dont care what it is as long as its not going to overtake or hurt anything (it's quickly spreading on this rock). It looks translucent an seems to have pores possibly, like a sponge, but it also seems to have protruding parts that protrude outward, and I am not sure if this is typical of a sponge. Here is a link to a bunch of hi resolution pictures:



http://publicfiles.sytechsolutions.net/rock_growth/



Thanks!