Here is a great video of the Lettuce Sea Slug from the Morphologic Blog. I’m normally not a fan of owning sea slugs due to their delicate nature and specific diet, but the Elysia crispata “Lettuce Sea Slug” is the exception. Unlike their counterparts, they don’t eat bryozoans, hydroids, or anything like that. Instead, the Lettuce Sea Slug eats green algae. Once ingested, the slug moves the chloroplasts from the algae into large fleshy appendages on its back. As their name suggests, these appendages look like lettuce sort of. The slug then uses the plant cells it has acquired to create energy, much like a plant does. This relationship has been around for an extremely long amount of time, even to the point that some slugs can create their own “plant cells”.
From a previous article we wrote (Elysia chlorotica is Part Plant, Part Animal):
The E. chlorotica slug has apparently stolen enough of the genes of its food source to actually make chlorophyll, a product required by the chloroplasts to make food. This discovery was made by researchers at the University of South Florida and shows that this slug is the first animal to actually produce this chlorphyll all on its own.