you might be able to do a clam in there, i haven't ever used PC so take my advice with a grain.
i can say with certainty that you would do fine with a large number of different soft corals. colts, zooanthids, green star polyps, mushrooms, even leathers.
if you wanna go stony i would stick with the "LPS" varieties they typically need less light to survive than "SPS" types but if you wanna try the "SPS" do some small aquacultured frags from a LFS or fellow reefer first before purchasing a larger colony.
i wouldn't try a clam until i was successful at keeping "SPS", clams are a bit spendy.