The Golden Jellyfish, cut off from the sea and now living in freshwater, has evolved to the point where it no longer needs stinging cells to capture its prey. Instead it has developed a symbiotic relationship with a type of algae that lives inside its tissues. The jellyfish alternately swims downward to expose the algae to a nitrogen rich environment, then upward toward the surface of the lake so that the algae can carry out photosynthesis and reproduce, ultimately providing a food source to the host jellyfish, which consumes just the right amount to balance its dietary needs while also sustaining algae population.
I watched an entire colony of hundreds of these jellyfish follow sunbeams around the lake, avoiding any shadows cast by the trees from the dense surrounding forest. I shot this individual right near the surface. You can see the sky and the clouds on one side of the frame and the dark area to the right is the edge of the forest.