Top 5 Nudibranchs of North Sulawesi
At Murex Resorts, every dive is a celebration of the ocean’s incredible diversity. Here, small is definitely beautiful—in addition to countless other critters, North Sulawesi is home to an estimated 350 species of nudibranchs, and there are still more new species being discovered.
From solar-powered sea slugs to leopard-print predators, and from ravenous carnivores to gentle grazers, nudibranchs embody the beauty, diversity—and downright weirdness—of the underwater wonders that make diving in North Sulawesi such an adventure.
In our latest blog article, we introduce a few of our personal favorites, exploring the characteristics and behaviors that make nudibranchs unique.
1. Costasiella Kuroshimae: The Graceful Grazer
Let’s start with a misnomer. You probably know this miniature marvel by its common name: Shaun the Sheep. Readers with a keen eye will have noticed this nudi is not actually a sheep—but did you know it’s not technically a nudibranch either?
Costasiella kuroshimae is a sacoglossa—a group of sap-sucking sea slugs from a separate clade to the better-known nudibranchs. While nudis are generally carnivores that feed on sponges, hydroids, and sometimes other nudis, their more mild-mannered sacoglossa cousins are herbivores who graze on plants. Some of these critter cattle, like our friend Shaun here, can even ‘farm sunlight’ from the algae they eat, in a process called ‘kleptoplasty’.
The name may be a little misleading, but one thing is certain: encountering this tiny treasure, munching on seaweed in the muck of the Lembeh Strait, is one of the most incredible macro encounters North Sulawesi has to offer—and a feast for the eyes of underwater photographers diving with Murex Resorts.
2. Nembrotha Kubaryana
Known informally as the “variable neon slug,” Nembrotha kubaryana is a showstopper in green and black with vivid orange-red gill plumes. It’s one of the larger dorid nudibranchs you’ll encounter, sometimes reaching 12 cm, and has a wonderfully deliberate way of moving across the reef.
This species is regularly spotted at Murex Bangka, where its diverse reef systems — from shallow coral gardens to deeper pinnacles — provide ideal hunting grounds for the tunicates it feeds on.
3. Goniobranchus Leopardus: The Colorful Chemist
Another common nudibranch species of North Sulawesi, this one uses color to deter potential predators. True to its common name, the leopard nudibranch wears a snazzy pattern of brown-to-gold spotting over a pale body.
Its main defense is a body packed with toxins, which it absorbs from the sponges it eats. By imbibing these chemicals, and advertising them through eye-catching coloration, the leopard nudibranch avoids becoming a meal.
These amazing patterns, when framed against reef, rubble, muck or substrate, also make this spectacular nudi species a favorite subject for underwater photographers in North Sulawesi.
4. Melibe Colemani: A Floating Phantom
One of the rarest and most extraordinary critters in North Sulawesi, the ghost nudi (Melibe Colemani) is almost transparent, lives on xenia soft coral, and feeds with a bizarre expandable oral hood.
Unlike most nudibranchs (which tend to graze or scrape to get a meal), this species is a filter-feeding predator—closer to a Venus flytrap than your typical sea slug. Their relatively small bodies (just 1-2 cm) are covered in branching, leaf-like cerata that resemble algae, which help it blend into its surroundings.
With this camouflage, ghost nudis can be hard to spot. Luckily, Murex dive guides know where to look and are adept at reading the reef for telltale signs of these fascinating phantoms; every time we spot one around Bangka Island, they immediately become a hot topic of conversation among guides and guests at the resort for the rest of the day.
5. Pteraeolidia Semperi: Solar-powered Sea Slug
Last but by no means least, this long, graceful aeolid—often called the blue dragon—is one of the larger facelinids and, like some Phyllodesmium, is famous for harboring symbiotic algae that help power its languid lifestyle on the reefs of North Sulawesi.
One of the most fascinating nudibranchs of North Sulawesi, Pteraeolidia semperi forms a symbiotic relationship with algae—a rare trait among nudibranchs. It hosts zooxanthellae (symbiotic algae) within its body and, when these plants photosynthesize, they provide their host with supplementary energy.
This nudibranch is different from sacoglossans like Shaun the Sheep—instead of stealing chloroplasts, it maintains living symbiotic algae within its tissues. This makes this beautiful blue dragon unique; a tiny ecosystem, floating through a world of miniature marvels.
Explore More with Murex!
Ready to discover the many nudibranchs of North Sulawesi for yourself? At Murex Resorts, we provide guided dives to locations like Bunaken, Bangka, and Lembeh, where nudibranchs proliferate among countless other critter species.
For more information, and to begin booking your own dive adventure in Indonesia, please visit the Murex website or get in touch. A world of wonders—both great and small—is waiting for you!
Want to learn more about diving in North Sulawesi? Check out these blog articles, which reveal the amazing biodiversity to be explored here:
- Top 10 Dive Sites in North Sulawesi
- Top 5 Marine Animals in Bunaken
- Top 5 Marine Animals to Spot On Your Diving Trip to Bangka
- Boxing Clever: The Peacock Mantis Shrimp
- Frogfish: Masters of Disguise
For a closer look at the five sea slugs featured in this article, along with 18 other nudibranch species of North Sulawesi, watch our latest video on YouTube.
