Elysia crispata

This Mystery Organism is Elysia crispata, the leafy sea slug. Formerly known as Tradachia crispata, this lovely sea slug, or opisthobranch mollusc, lives in the Caribbean Sea in a variety of shallow water habitats. A very closely related species, Elysia diomeda, is found on the Pacific Ocean side of Central America as far north as Baja California (see photo below). These two species provide another great example of speciation through geographic isolation - the two bodies of water have been separated by a land barrier for only a few million years.

Like its snail relatives, Elysia crispata uses a rasping organ (radula) to cut into its food - in this case a number of species of green algae. But what it does with its food is rather unique! It digests away the tissues but not the algae's light harvesting organs - the chloroplasts.

Instead, Elysia holds on to these tiny powerhouses and distributes them throughout the surface tissues of its own body. In the enlargement on the left, you can see the green clumps of chloroplasts lodged inside Elysia's cells! Here they aactually function normally, as though they were still in the body of the algae. They harvest light and contribute food to the host sea slug. This type of symbiosis is called kleptoplasty (stealing chloroplasts). Elysia crispata (and several other species of this genus) really is 'a leaf that crawls'.

Photo at Right: Elysia diomeda, the sister species to Elysia crispata found on the Pacific side of the Central American land barrier.

For a great teaching tool about molluscs that features nudibranch reproduction and life history, see our program, Branches on the Tree of Life: Molluscs.

If you'd like more information on nudibranchs and other sea slugs, visit Bill Rudman's great sea slug site!