The sea slug.
Next year we’ll be going into the differences between plant and animal cells, as well as into the differences between plants and animals. There are a number of fundamental differences, starting with the fact that plants can photosynthesize to convert sunlight directly into energy and animals can’t. Except for the sea slug. Sea slugs have found a way to pirate chloroplasts from green algae (found via Immersion Blog).
Chloroplasts are the green cellular bodies (organelles) that perform photosynthesis. The species Elysia chlorotica eats the algae when they are young and instead of digesting them entirely, keep the chloroplasts in their gut.
Young E. chlorotica fed with algae for two weeks, could survive for the rest of their year-long lives without eating – Brahic, 2008
What’s even more intriguing is that there is evidence that the sea slugs have incorporated parts of the algae into their own DNA so they can maintain the right conditions for the chloroplasts to survive in the new host (Rumpho et al., 2008). The Sea Slug Form has a nice page on other solar-powered slugs.