This sea slug actually acquired the ability to photosynthesize. As far as I can tell, this guy seems to be mid-evolution (aren’t we all?). The slug steals chloroplasts from the algae it eats, but it does not incorporate the entire algae cells. Chloroplasts can’t perform the whole photosynthesis chemical reaction all by themselves, but rather need some genes/proteins from the host algal cell. This sea slug has incorporated the actual genes from the algae into its own cells, thus this guy really seems to be a plant/animal hybrid! It even has the extra genes in its gametes, so its offspring may not even need to do the steal-the-genes trick!
There is still a step left to truly transform this guy into a plantimal. I don’t believe the chloroplasts can be transferred to its offspring. Once this happens though, this animal would never have to eat anything! Super cool.
By the way, if this sounds at all fanciful to you, it’s not that surprising. The cellular energy factories called mitochondria that are in most of your cell types were acquired in a similar fashion — though i suspect it was single-cell-guy eating single-cell-guy. This is pretty different I guess.