My CB shrimp (one of them any way) are Houdini-ites. I added one to the tank and after the second day it was gone. Figured it was crab poo. A couple months later I got a new one. The next morning I thought I was seeing double. Two shrimps and as luck would have it they paired up, no WWF in the tank. I wouldn't have been so shocked except that my tank is in the living room, I am home all day and don't have a huge amount of rock in the tank. I can't believe that thing was able to stay out of sight for a couple months.