10/07/2025
Elysia chlorotica, a remarkable species of sacoglossan sea slug found along the east coast of the United States and Canada.
What makes this slug exceptional is its ability to perform photosynthesis — a trait almost unheard of in the animal kingdom.
Elysia chlorotica achieves this feat through a process called kleptoplasty, where it "steals" chloroplasts from the algae (Vaucheria litorea) it consumes.
These chloroplasts are incorporated into the cells lining its gut, allowing the slug to harness solar energy — effectively turning it into a “solar-powered” organism.
It’s not quite true photosynthesis as in plants because the slug doesn’t have the full genetic machinery for it.
Instead, it appears to use some horizontal gene transfer to partially support the stolen chloroplasts for weeks or even months.
This discovery was first detailed in the early 2000s and remains one of the most fascinating examples of symbiosis and gene transfer across biological kingdoms.
Although it is not the only photosynthetic animal (other sacoglossan slugs also exhibit similar behavior), it was the first known and is still the most studied.