This beautiful leaf-shaped sea slug Elysia chlorotica lives in shallow pools along Atlantic coast of North America, eats algae with gusto - one meal is enough for its lifetime!
and by using photosynthesis like any other plant, shatters the most basic definition between the "animal" and "plant" kingdoms. It may not be "easy being green", but for this slug it turned out to be highly efficient!
This is the ONLY natural example of genes shared between the living kingdoms of "plants" and "animals". Shaped like a leaf? Check. Totally colored green? Check, although the young slugs are still colored brown until they eat their first "green" meal... but right after that, they're ready to make pigment chlorophyll a all by themselves for the rest of their lives!
One thing about Elysia chlorotica, "a sea slug that has stolen enough genes to become the first animal shown to make chlorophyll like a plant". They don't just use chloroplasts from the algae they eat - this phenomenon, though rare, is known as kleptoplasty. What's more, they seem to have the particular genes that make them able to keep processing these chloroplasts in a consistent and sustainable way.
Consider Elysia chlorotica: when it comes to consuming chloroplasts, one slurping is enough! "It's the ultimate form of solar power: eat a plant ONCE, become photosynthetic for the rest of your life"