Where do berghia nudibranchs hide?

[Chrisv.]

I'm nearing the end of a tank upgrade. I transferred all of my rock and most of my sand to the new tank (with more rock and more sand) and I'm wondering what the chances are that the nudibranches I bought a couple of weeks ago made it through the move. My unfounded concern is that they might be in the sand of the original tank (it's still running, but without rock and coral).

So...where do they hide? Do they hide in the cracks in the rocks, or do they dig into the sand during the day?

 

[tbrown]

On the bottom of rocks and I'm crevices. I rarely see mine in the sand but occasionally they'll be on the sand, not in it though.