Photos of  Costasiella kuroshimaea.k.a. the “leaf sheep” sea slug, have recently gone viral on Twitter again, and for good reason. The leaf sheep doesn’t just have an absurdly cute name, it also has an absurdly cute face. It really does look like a Pokémon. On top of that, the sea critter belongs to the only multicellular-animal clade that can photosynthesize light into food.

The Leaf Sheep Sea Slugs Performs Photosynthesis

The leaf sheep is such a precious sea slug. What you’re looking at in the photos is the leaf sheep’s eyes and mouth, as well as its cerata. The cerata are the leaflike appendages that cover the leaf sheep’s body and are filled with algal chloroplasts. Chloroplasts, for those who don’t remember middle school bio, are organelles that conduct photosynthesis using chlorophyll.

In a process referred to as “kleptoplasty,” the centimeter-long leaf sheep sea slug grazes on green algae, then retains the consumed chloroplasts. It uses those chloroplasts to photosynthesize energy from light into usable energy—i.e. food. As a result, solar power alone can satiate the sheep slugs for months on end. Yes, the leaf sheep sea slug is an animal that can perform photosynthesis.

Where can you Find the Leaf Sheep?

For those wondering if leaf sheep slugs are as cute in motion as they are in still portraits, the answer is yes. In the video above, the undersea cuties use their Heffer-like mouths to scour the ground for algae. Literally every single aspect of the leaf sheep is cute. Even their big wiggly horns, referred to as rhinophores, look cute smelling out surrounding seawater.


Unfortunately, the leaf sheep are native to the waters around Japan, which means they’ll be hard to see for many of us. Although, in the eastern emerald elysia, another sea slug belonging to the clade, Sacoglossa, resides along the east coast of the U.S. The eastern emerald elysia (below), like the leaf sheep, can perform photosynthesize light into food. Although it’s not nearly as cute.

Everything Old Is New Again

Hilariously, the leaf sheep sea slug goes viral again and again.

But we applaud this trend. If there was ever a creature that deserved internet fame, it’s this one. Three cheers for you, leaf sheep.

Originally published on July 23, 2020.