Other than the new building blocks, that looks suspiciously like a new kind of light block as well.
And I can tell you all right now, the way to hit these temples is going to be from underneath.
Locate it and, from a distance, drop to the bottom and tunnel in. That way, you'll have air and protection from the baddies. Get under it, tunnel up and swipe the goodies!
You'll be able to block up the entrance to keep the "fish" out and run wild with the interior. Take buckets along to remove water, or netherrack for quick water-blocking-out, etc. Other than the fish, these will be easy picking, I think.