Some sea slugs can perform a remarkable trick: they keep chloroplasts taken from the algae they eat and use them to capture sunlight. This process, called kleptoplasty, does not make the slugs plants, but it lets functioning algal machinery continue photosynthesis inside an animal’s cells for surprisingly long periods underwater.
How chloroplast theft works
Sacoglossan sea slugs pierce algal cells and suck out their contents. Instead of digesting everything, certain species retain chloroplasts within cells lining their branching digestive system. The captured organelles are known as kleptoplasts. Exposed to light, they produce energy-rich compounds that can support the slug’s metabolism.
Famous green specialists
The emerald green Elysia chlorotica is the best-known example. It obtains chloroplasts from Vaucheria litorea and may preserve their activity for months. Elysia timida also stores working chloroplasts, while other sacoglossans keep them only briefly. Their leaflike shapes and green coloring can make these mollusks resemble seaweed.
What photosynthesis provides
The stolen chloroplasts are not a complete replacement for food. Instead, photosynthesis acts more like a nutritional supplement. Research indicates that kleptoplasts can generate sugars and fatty acids, helping with survival, growth, reproduction, mucus production, and tissue repair. Benefits vary among species and depend on available light.
Why scientists are fascinated
Keeping chloroplasts functional outside algae is difficult because these organelles normally rely on proteins supplied by the algal cell. How slugs protect and maintain them remains an active research question. The mystery may reveal new insights into cell biology, evolution, and extraordinary partnerships between unrelated organisms.
More surprising animal adaptations
Kleptoplasty shows that the boundary between plantlike and animal abilities is less rigid than it appears. These slugs remain animals, yet they temporarily borrow one of nature’s most important solar technologies. For an example of evolution’s engineering, explore how rectangular pupils help animals scan their surroundings.