The Secret Aquarium - 8 Red Coins

N64
We open the door with the 3 on it the right of Whomp's Fortress. It's a peaceful room with a couple of aquariums. On the left and right walls are two nooks. The one on the left has a 1-up and the other has the entrance to a secret course. Soothing, peaceful music plays as we find ourselves underwater (this is the version of the underwater music with the more uptempo beat). Swimming is like flying with the Wing Cap: press up to dive and down to surface. There are several coins, but there is nowhere to surface for air. With every passing moment, our Power Meter ticks down, but we can recover our health with coins, 1 bar for Yellow Coins, 2 for Red Coins, and 5 for Blue Coins. The windows are tinted with the colors of the towers in the Wing Cap Course. What's in here? There is a school of harmless fish, that won't affect you in any way. There is also a blue horizontal star, which means there are 8 Red Coins to get! Four of them are in the center of coin rings. The other for are on the floor of the aquarium in the corners. The are less than 100 coins here, so don't worry about getting the rest for another Star. Once we got all 8 Red Coins, the Star appeared in the center of the aquarium, on the floor.
Star Get #16, 28 Coins, 7 Lives

Nintendo DS
I entered the door to the right of Whomp's Fortress and got the 1-up in the left nook. I then entered the Secret Aquarium. The Red Coins are in the same place as in the N64 version. Soon, I had all 8 Red Coins and the Star.
Star Get #12, 22 Coins, 5 Lives
We get a message: "You've recovered 12 Power Stars! Now you can open the door with the big Star! But Bowser is just ahead... And is that the sound of the princess calling for help?"
We can't battle Bowser just yet, nor do I want to. I want to get as many Stars as possible before I tackle Bowser.
The next Star is Plunder in the Sunken Ship.