The elysia chlorotica is the only animal known to use photosynthesis

The elysia chlorotica is a sea slug that lives in the cold waters of the Eastern and Western coastal United States. It is the only known animal to steal the genes of plants and algae and use photosynthesis to feed itself. Scientists have proven that the snail is not only harboring plants on it, but has actually stolen genetic code and embedded it in itself. Scientists' most comprehensive test to prove that the slug produced the chlorophyll enzymes on its own involved them injecting the slug with an amino acid. They found that the slug only produced chlorophyll a when it was in the light and not in the dark.
This theft of genes has made the sea slug the first solar-powered animal and a true hybrid between plant and animal

sources: wired.com/weirdscience