Great advice Anthony, on all counts.
Melina, I dont see why you could not keep a derasa or squamosa as mentioned, esp. with individual reflectors and running 6 bulbs.
Perhaps a crocea or maxima, but it would need to be higher up on the rock. You can purchase captive bred, small derasa,s all the time and that may be your best bet to start with.
Remember also, that squamosa & derasa clams can grow fairly large, so they need a spot to grow when first introduced and start attaching, if smaller clams.