All about Shaun the Sheep
I recently discussed the “Shaun the Sheep” sea slug with some friends. The animal we are talking about is Costasiella kuroshimae, a sea slug often called Shaun after a cartoon character. It’s a curious animal, for several reasons. Let’s go over a few of the Shaun-related topics which came up:
How to Find Shaun
First you have to find this semicircular seaweed: Avrainvillea. In Dauin, in the Philippines, where I dive, the slug is always found on this seaweed. I have never seen it anywhere else- but this might be different in other locations. Avrainvillea grows in soft-bottom habitats, no deeper than 12 meters (again, that’s my observation from Dauin), and sometimes up to shallow depths of 3 meters.
Not every leaf of Avrainvillea has a Shaun, but in Dauin probably every 5th or so has. They are not uncommon, and you’ll be find them on every dive once you have the search pattern for the animal figured out. I have the impression that “cleaner” leafs of Avrainvillea, with less filamentous algae and detritus, are more likely to be home to the slug.
Also, the mollusk is tiny … I’d say 4 mm long for the largest individuals. You have to use a camera with a close-up lens, or a magnifying glass, or have excellent near vision. Once you have seen the slug a few times, you’ll be better at spotting him without being able to resolve the shape of his body.
Who is Shaun?
Firstly: Shaun is not a nudibranch, but a different type of shell-less gastropod mollusk (“slug”), a Sacoglossan. Related, but not the same. I have the impression that Dauin has a few species of Costasiella, probably the Costasiella kuroshimae, the slug named “Shaun the Sheep” originally, and a few closely related species. The blue/yellow slug is almost certainly a separate species. I’d love to hear from molluskan taxonomists to find out if there is new work on these.
Who else lives on Avrainvillea?
I have noticed that a number of other animals live on Avrainvillea: Gobies, skeleton shrimp, and occasionally squat lobsters. In the seagrass, close to the Avrainvillea, a unique fauna of crustaceans, fishes, and of course green turtles thrives.
Why is Shaun so Green?
The green color of this seas slug is due to a unique trick these Sacoglossans use: they keep the “solar power plants” of the algae alive and use their ability to produce biological energy from sunlight, long after having eaten the algal tissue. I explain this in detail here:
I hope this summary is interesting and useful for the underwater naturalist,
Best Fishes,
Klaus
