Small enough to fit on your fingernail, bright green like a cartoon salad, and sporting tiny “ears” that look like sheep horns, this sea slug is pure underwater joy. Meet Costasiella kuroshimae, affectionately known as the ‘Shaun the Sheep’ nudibranch.
There’s something about it that makes you want to know more. What is it? Where does it live? In the pages ahead, you’ll get to know this little wonder. If you’ve ever dreamed of meeting a creature that looks like it swam out of a fairy tale, you’re in the right place.
What Is ‘Shaun the Sheep’ Nudibranch?
The ‘Shaun the Sheep’ nudibranch, or Costasiella kuroshimae, is a tiny sea slug first described by scientists in 1993 near Kuroshima Island in Okinawa, Japan. It belongs to a group called sacoglossans, which are algae-eating sea slugs often confused with nudibranchs.
Wait, are they not nudibranch then? Nope, they aren’t technically the same, but sacoglossans are just as charming. This one earned its nickname thanks to its uncanny resemblance to the cartoon sheep so many of us grew up watching.
What makes this nudibranch stand out is how it looks. It has two black-tipped rhinophores that stick out like sheep ears, a plump little body, and a face that somehow seems to smile. Its back is covered in soft green spikes called cerata, which help it blend in with algae and also do something amazing: they let the slug use sunlight to make energy.
Why Is the ‘Shaun the Sheep’ Sea Slug So Unique?

The ‘Shaun the Sheep’ nudibranch doesn’t just look like something out of a cartoon. It also has a rare ability that most animals don’t: it can indirectly make its energy from sunlight through kleptoplasty. After eating a certain type of green algae, it keeps tiny parts of the plant called chloroplasts inside its body. These parts are like little solar panels that let the slug turn sunlight into energy via photosynthesis.
Although this process sounds complex, picture it like this: the slug eats salad and then becomes part plant for a while. That’s also why it looks so green. Its soft leaf-like back glows with the color of the algae it’s been snacking on.
Where Can You Find ‘Shaun the Sheep’ Nudibranch?
‘Shaun the Sheep’ nudibranchs live in warm, shallow waters throughout the Indo-Pacific. They tend to stay close to algae-covered rocks, black sand slopes, or soft rubble bottoms. These slugs are small and well-camouflaged, so having a knowledgeable guide helps.
If you’re hoping to see one for yourself, here are three great dive destinations where they are often found:
- Lembeh Strait, Indonesia – Famous for muck diving and rare critters, Lembeh is one of the best places in the world to find this nudibranch. Its black volcanic sand and algae-rich sites create the perfect home.
- Anilao, Philippines – Another macro hotspot with a wide variety of sea slugs and excellent conditions for photographers.
- Okinawa, Japan – Close to where the species was first discovered, Okinawa offers beautiful algae patches where these slugs are still spotted today.
Each of these places has calm waters, shallow depths, and the right kind of algae that can support their life, making it the ideal spot to see this tiny, glowing “sheep of the sea.”
5 Tips to Spot Nudibranch Underwater
‘Shaun the Sheep’ nudibranchs are usually just around 5 to 10 millimeters long, so finding one isn’t always easy. But with a little patience and the right approach, you’ll start to see how rewarding the search can be. Here are five simple tips to help you spot them on your next dive:
- Go slow – Move gently and take your time. Nudibranchs don’t run, but if you rush past, you’ll miss them.
- Look closely at algae – These slugs often hang out on or near green algae patches, where they feed and blend in.
- Ask your guide – Local dive guides know the best spots and can often point them out within seconds.
- Get low and scan the sand – Many nudibranchs live close to the seabed. A careful look around black sand or rubble can reveal hidden gems.
- Use a macro lens – If you’re taking photos, a macro setup helps you capture their tiny features clearly and beautifully.
Want to See One for Yourself?
If spotting a ‘Shaun the Sheep’ nudibranch is on your list, Lembeh Strait is the perfect place to find them! These tiny sea slugs live quietly among algae-covered sand and rubble, and with the right timing and focus, you can witness one grazing like a glowing leaf in the current. But at just a few millimeters long, they can be nearly impossible to find on your own.
That’s why at Solitude Lembeh Resort, our local PADI-certified guides are here to help. They know the sites, the algae patches, and the subtle signs to look for. With their help, your critter treasure hunt will be much simpler with an experienced guide on board. Not only that, after a rewarding day underwater, you can relax in your private villa, enjoy a home-cooked meal, and prepare for another day of underwater adventure.
Book your next adventure around Lembeh with Solitude today!