Shrimp die. All the time. It sucks. But it's the circle of life. They can be so hit or miss. That or it just molted and it's hiding. Did you find a molt?
[ame=http://www.youtube.com/watch?v=vX07j9SDFcc]YouTube - Lion King - Circle of Life[/ame]
Oh I have concluded it's gone haha I highy doubt it's eating. I could at least find a leg or antenna stickig out of the rock somewhere but now I can't see that even haha