There may be times when you want to shoot an unknown sessile critter in extreme macro, and the only way is to shoot it from INSIDE the tank
That underwater Reef Videoclip I posted awhile back on the main General Reef Discussion forum was shot with a Fuji Finepix A201 compact digital camera. It is not a waterproof camera by itself.
It was ably protected from the water by an Aquapac waterproof camera case, which I bought last Summer in the US (at a Sports Authority outlet). It is a British product, and involves a clear soft plastic pouch, with a hard plastic 'lens' for the camera to shoot through --this even comes with an attached 'lens cap' to protect it from scratches (this cap when open can bump into things when shoting macro in crowded quarters)-- all of it sealed with a hard-plastic locking device to keep water out.
So long as a camera's dials have a thumb knob, they are fairly easy to operate through the soft plastic. Slide switches are a little trickier, but manageable.
Since the waterproof pouch comes in only a few sizes, your camera may be too small, and this can make aligning the camera lens with the pouch 'lens' tricky. Stuffing the bag with tissue paper for a slightly tighter fit may work (you still want some looseness to operate the camera switches). Or you can just align the two 'lenses' for each and every shot.
hth,
horge