Elysia crispata, a sea slug, is found in the tropical parts of the Caribbean and the western Atlantic. Here it can grow up to 5cm, although most specimens hardly grow larger than 3cm. Its bright green, frilly edges make Elysia crispata resemble a lettuce, hence its common name: the lettuce sea slug. These conspicuous protrusions are called parapodia. But the the similarities between this mollusk and the vegetable go even further: adult Elysia crispata are able to use kleptoplasty as a source of energy. This means that the chloroplasts of the algae they feed on are absorbed into their cells and stored in their parapodia. The chloroplasts remain there for more than a month, depending on the type of alga. They continue to perform photosynthesis there, nourishing the slug.
Sources: Händeler, Katharina et al., “Functional chloroplasts in metazoan cells: a unique evolutionary strategy in animal life”, Frontiers in Zoology, vol. 6, issue. 28, (2009).