Moon jelly backlit

This is a moon jelly, a specific species of jellyfish. It's about 12 to 14 inches wide, and it's absolutely intriguing to watch. This photograph is unusual in that you usually don't see brilliant backlighting behind these ephemeral creatures. I took this shot at the Tennessee Aquarium in Chattanooga. Several moon jellies live in a floor-to-ceiling cylindrical aquarium that is about 6 to 7 feet in diameter. I asked my wife to stand on the opposite of the aquarium and hold a flash pointing at my camera. I didn't have a remote trigger because I wasn't expecting to need it. So, I set my shutter speed to one full second, the lens aperture to f/22 for maximum depth of field, and the ISO was 100. Hand holding the camera, I counted 1, 2, 3, and when I hit three my wife manually tripped the flash. On the count of 2, I opened the shutter so I could record the flash. It took a few test shots to get the exposure right.