What is this fish?

[BCShelly]

I don't normally shop Total Pet, I was looking for some floss and found the 1/2 price rock. It's covered with those star looking plant things (can you tell I'm new) and thought it was a good deal. Turned out it was! Yes, my tang went missing in the night as did one of my chromis the next night. No sign of anything in the AM. I have set traps 2 nights in a row (raw mussels in tupperware) to see if I could catch anything. Got up at 3AM this morning and only my hermit crabs were in the trap. Any idea's? My water is fine, the fish weren't sick, just poof, disappeared.