Carnivorous plants don't count as they don't use their prey for energy. Photoheterotrophs don't seem to fit based on a quick read as they use light and carbon in the same reaction. I'm looking for something that both eats for energy and does photosynthesis for energy. A select few animals that are symbiotic with algae barely fit. But is there a reason why 99.9999999% of organisms choose one or the other?
As an example, why couldn't some seaweed evolve to catch plankton like an anemone?