My fiddler crab is missing?

I bought a fiddler crab yesterday. I put it in a tank with the water filled halfway up and put stuff in there so that it could climb out of the water to get air. Well this morning I was looking for it and it wasn't there. I poked around with a net for a few minuets. Then I removed all the substrate handful by handful and searched through it. I removed my filter and checked in there. What could have happened to it? I have a hood on the tank so it didn't just climb out. Please help?