Elysia (gastropod)

Elysia is a genus of sea slugs, marine gastropod molluscs in the family Plakobranchidae. These animals are colorful sea slugs, and they can superficially resemble nudibranchs, but are not very closely related to them. Instead they are sacoglossans, commonly known as sap-sucking slugs.

Elysia sea slugs graze on algae and some species such as E. viridis and E. chlorotica hijack the chloroplasts for themselves. The chloroplasts end up lining the slug’s digestive tract, enabling the slugs to survive solely by photosynthesis for several months at a time. This association is crucial for the development and maturing of the slug. Exactly how the slugs use the chloroplasts is unclear, as many of the proteins used are encoded in the genome of the host cell. These proteins, numbering in the hundreds, are manufactured in the cell’s nucleus, and then moved into the chloroplast, enabling it to survive.

This genus was previously sometimes considered to be in the family Stiligeridae, and was also previously placed in the family Elysiidae.