I mentioned this animal in class when we were discussing photosynthesis.

This beautiful green leafy organism is actually a sea slug. The sea slug Elysia chlorotica consumes chloroplasts when it eats the algae Vaucheria litorea. The slug feeds on the algae, but the chloroplasts are retained in the cells of the gut. The gut in this sea slug is highly branched and the chloroplasts give it the green color. The chloroplasts in the tissue of the animal's gut continue to function in the animals without an algal cell being present. The slug lives about 10 months and can survive off the food made by the chloroplasts.

The green color also provides great camouflage. While the animal has to eat an algae to get the chloroplasts, it is intriguing that the chloroplasts can continue to function without any algal cells present as genes in the nucleus of the algae are needed for photosynthesis to occur. So where are the genes to support photosynthesis? In the nucleus of the sea slug cells! The slug gets the genes from the algae, it does not have them until the animal feeds on the algae.

Interested in looking into this gene transfer further? Click here to read a paper by Mary E. Rumpho et al. on horizontal gene transfer between the algae and the slug.