This is a moon jelly. I photographed it in the Tennessee Aquarium in Chattanooga. These animals are displayed in a large cylindrical acrylic aquarium about 6 feet in diameter from floor to ceiling. It's in a very dark room, and there are colored lights illuminating the exhibit. I didn't like the artificial colors, and I wanted to show how intriguing the moon jellies are by using backlighting. So, I asked my wife to hold my flash on the opposite side of the tank. I used a 50mm macro lens so, as the animals drifted close to the acrylic, I could focus on them just inches away. At the time, I didn't have a remote trigger for the flash with me. Therefore, I used a one-second exposure, and during that time my wife manually triggered the flash. I composed the shot so the subject blocked my view of the flash. I chose f/22 for as much depth of field as possible, and the ISO was 100. It took several test shots to get the exposure just right.