Sacoglossa

Now I know I said nudibranchs were my favorite gastropod, but some of these gastropods really made me have reconsider that comment. The gastropods that belong in the sacoglossa category are very interesting to say the least. They are also called "sap-sucking sea slugs", that are called this because their food source is the cellular contents algae. They are divided into two groups, one of which has a shell and are called Oxhynoacea. The other group that does not have a shell (called Plakobranchacea) is the reason why I had to reconsider my favorite gastropod. Plakobranchacea have evolved to use kleptoplasty, which allows them to maintain chloroplasts from the algae that eat and actually use the photosynthetic products as their primary food source for months. Some have "wing-like" structures to increase the surface area for photosynthesis. Some have also adopted the color of algae (because of the chloroplasts in their bodies).

Plakobranchacea with "wings" spread:

Plakobranchacea with "wings" unspread:

Green Sacoglussan: