Elysia

Elysia is a genus of sea slugs, They are marine gastropod molluscs in the family Plakobranchidae. These animals are very colorful. They can look like nudibranchs, but are not very closely related to them. They are sacoglossans, commonly known as sap-sucking slugs.
"Elysia" sea slugs eat algae. Some species such as "E. viridis" and "E. chlorotica" use the chloroplasts in the algae for themselves. The chloroplasts line the slug’s digestive tract. It lets the slugs live by photosynthesis for several months at a time. Exactly how the slugs use the chloroplasts is unclear. Many of the proteins used by chloroplasts are encoded in the genome of their cells. There are hunreds of these proteins. They are made in the cell’s nucleus. They are then moved into the chloroplast. This lets the slug.
This genus was said to be in the family Stiligeridae. It has also been placed in the family Elysiidae.