Part animal, part plant, bright green, and totally bizarre: Meet the sea slug Elysia chlorotica.

Biologists already knew that this organism, native to the marshes of New England and Canada, was a thief that somehow pickpocketed genes from the algae it eats. At last week’s meeting of the Society for Integrative and Comparative Biology in Seattle, researcher Sidney Pierce said he has found that the slugs aren’t just kleptomaniacs—they use the pilfered genes not only to make chlorophyll, but also to execute photosynthesis and live like a plant. Said Pierce: “They can make their energy-containing molecules without having to eat anything,” Pierce said. “This is the first time that multicellular animals have been able to produce chlorophyll” [LiveScience].

The slug steals in a different way than most organisms (usually bacteria) that employ horizontal gene transfer to incorporate the DNA of others. Most of those hosts tuck in the partner cells whole in crevices or pockets among host cells. Pierce’s slug, however, takes just parts of cells, the little green photosynthetic organelles called chloroplasts, from the algae it eats. The slug’s highly branched gut network engulfs these stolen bits and holds them inside slug cells [Science News].

By using detectors to trace small amount of radioactivity, Pierce says he confirmed that the slug was actually using the stolen genes to produce the chlorophyll itself rather than snatching already-made chlorophyll from the algae. In addition, parent slugs pass on the genetic pathways for chlorophyll and photosynthesis to their offspring, showing it becomes incorporated into their genes.

Once again, nature reminds us, evolution can be wonderfully creative. “This could be a fusion of a plant and an animal — that’s just cool,” said invertebrate zoologist John Zardus [Science News].

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Image: Nicholas E. Curtis and Ray Martinez