blue boxfish

[Kabong]

The black one's with the white spot's are actually the female of the blue boxfish.

As for boxfish in general, My understanding is they are considered "advanced" fish because they have some specific requirments. As in
#1 they are poor swimmers so they require a slower flow then most reef tanks have.
#2 they need to be fed under the water (no surface feeding) air in there digestive track can be fatal
#3 they cant be kept with cleaner fish, there "cleaning" can actually damage the box fish's skin.
#4 they may make a snack of your corals and or inverts.