Is this a type of sponge?

[DanBeck]

I found this organism under my a rock when I was trying to catch a crab. It was growing under the rock where the light doesn't reach.
Any ideas of what this may be?

 

[ISpeakForTheSeas]

I'd guess that it's a cryptic sponge of some kind, though I can't say that I'm familiar with this specific kind.