The curiosities of the Blue dragon nudibranch

Commonly referred to as the Blue dragon nudibranch, Pteraeolidia ianthina (Nudibranchia - Facelinidae), is a remarkable species of sea slug native to the Indo-Pacific region.

This is an extremely elongate species up to 5cm long, with large, curved arches of cerata (the projections on the upper surfaces of the body) along the length of the body. The cephalic tentacles have two distinctive dark purple (or blue) bands.

Although the body color of this nudibranch is translucent tan, the cerata, which are mostly blue or dark purple, lavender or golden brown, give the nudibranch most of its apparent color.

The Blue dragon nudibranch has many amazing survival strategies. When touched, the nudibranch will “flare” its cerata and the nematocysts will discharge on contact (it is one of the few nudibranchs with a sting strong enough to be felt by humans though usually not in areas with thicker skin such as the palm of the hand).

It is also able to autotomize (lose or detach) the posterior part of its body in order to distract, or free itself from, a potential predator. Later, the missing portion can be regenerated.

Another curiosity of this species is that the cerata contain zooxanthellae of the genus Symbiodinium that exhibit the capacity for photosynthesis, and they grow while reside in the sea slug. This symbiotic relationship with the algae helps the adult nudibranch to overcome a period of food shortage by getting photosynthetic products.

References: [1] - [2] - [3] - [4]

Photo credit: ©Sylke Rohrlach

Locality: New South Wales, Australia

Made with Flickr

Glaucus Atlanticus.

Also known as sea swallow, blue sea slug, blue angel or blue dragon, it is a small sized sea slug that lives in the Atlantic, Indian and Pacific ocean.

They feed mainly on other sea creatures like the Portuguese Man-o-War, a cnidarian often mistaken for a jellyfish. The Glaucus is immune to their venom, and can actually store it in its cerata ( their dorsal and lateral outgrowths on the upper surfaces of the body). As a result they can sting potential predators. The sting is quite painful for humans, so they should be handled carefully.
At times, and given the occasion, they can be cannibalistic.

With the aid of a gas-filled sac in its stomach, the Glaucus floats at the surface. Due to the location of the gas sac, the sea swallow floats upside down. 

Like almost all heterobranchs, Glaucus is a hermaphrodite, having both male and female reproductive organs. After mating, both animals produce egg strings.


This is a Blue Sea Slug.

This is a Sea Swallow.

This is a Blue Ocean Slug.

This is a Blue Dragon.

This. Is. Beautiful.

If ever you’re confused as to the name, just use the scientific one, Glaucus atlanticus. When in doubt, Latin.

Anyway, the Blue Dragon is a type of nudibranch, which means it’s a mollusk without a shell (easy for me to remember because, well… nudey-branch… no shell… I know it’s silly, but it’s easy to remember). It is venomous, too – which means if you’re a kid in Australia and a bunch of these wash up on shore one day, they’re… good fun to… throw at your friends?! That’s right. Kids in Australia throw these little beauties at their friends, they’re called “Bluebottle” fights. Don’t have a “Bluebottle” fight. These are animals, leave them alone.

What I really wanted to talk about with these was the finger-like projections… the whispies… They’re called cerata, and those are the organs where the Blue Dragon stores the stinging cells that it steals from the jellyfish that. it. eats.

Pretty cool, right? Yeah, yeah it is. But this precious little 4 cm slug doesn’t just eat any old jellyfish, this is a dragon we’re talking about. The Glaucus atlanticus eats the Man O’ War jellyfish – and just so you know, the Blue Dragon concentrates the venom that it collects and can produce a more deadly sting than the Man O’ War jellyfish. Can’t find a Man O’ War jellyfish, just a bunch of other Blue Dragons? That’s okay as well, sometimes they become cannibalistic.

But hey, they’re pretty, right?

Blue Sea Slug (Glaucus atlanticus)

Kingdom: Animalia
Phylum: Mollusca
Class: Gastropoda
Superfamily: Aeolidioidea
Family: Glaucidae
Species: G. antlanticus
Size: 3cm
Diet: Larger pelagic organisms like Portuguese Man o’ War, by-the-wind sailor, blue button, and violet snail
Distribution: Temperate and tropical waters like the East and South Coast of South Africa, European waters, east coast of Australia and Mozambique
Facts: The sea slug preys on poisonous organisms to them save their poison to use for its own protection.  It also floats upside down on the surface tension of the ocean water.


This is the blue dragon sea slug, also known as Glaucus atlanticus.  Not only is the blue dragon immune to its sting, it’s able to process the Man o’ War’s nematocysts, the cells that allow for that creature’s deadly sting, and store them in its own extremities. Those venomous cells can be used by the blue dragon later on, and in a higher concentration, making their sting even more deadly.


On that topic, people often think that Goodra is partly based on this blue sea dragon sea slug, Glaucus atlanticus

but that looks nothing like Goodra

Understandably, It’s probably because the Glaucus atlanticus is really well known, i.e. it IS the dragon slug you first think of when you hear the words dragon + slug.

However, confusingly (and wonderfully)  there is another group of aeolid nudibranch sea slugs called blue dragons, the Pteraeolidia 

Which not only match Goodra’s colour scheme excellent but are called dragon sea slugs too!

Another closely related group also looks like our fave gooey dragon, the Phyllodesmium sp.

Anyway nudibranchs are SUPER COOL BRO

This tiny creature has gotten a fair bit of attention lately because of one simple reason: It’s absolutely crazy-looking. At first glance, it resembles a Pokémon or character from Final Fantasy more closely than a real biological animal. But the Glaucus atlanticus sea slug—commonly known as the blue sea slug or blue dragon—is indeed a genuine species. And if you swim in the right places off of South Africa, Mozambique or Australia, you just might find one floating upside down, riding the surface tension of the water’s surface.

The species has a number of specialized adaptations that allow it to engage in a surprisingly aggressive behavior: preying on creatures much bigger than itself. The blue dragon, typically just an inch long, frequently feeds on Portuguese man o’ wars, which have tentacles that average 30 feet. A gas-filled sac in the stomach allows the small slug to float, and a muscular foot structure is used to cling to the surface. Then, if it floats by a man o’ war or other cnidarian, the blue dragon locks onto the larger creature’s tentacles and consumes the toxic nematocyst cells that the man o’ war uses to immobilize fish.

The slug is immune to the toxins and collects them in special sacs within the cerata—the finger-like branches at the end of its appendages—to deploy later on. Because the man o’ war’s venom is concentrated in the tiny fingers, blue dragons can actually have more powerful stings than the much larger creatures from which they took the poisons. So, if you float by a blue dragon sometime soon: look, but don’t touch.


Weird animals Part 1 // Part 2

1. Blue Sea Slug - Galucus Atlanticus  (x)(x)

2. Gerenuk  - Litocranius Walleri  (x)(x)

3. Binturong - Articus Binturong  (x)(x)

4. Sunda Flying Lemur - Galeopterus Variegatus  (x)(x)

5. Tasmanian Giant Crab - Pseudocarcinus Gigas  (x)(x)

Glaucus atlanticus, commonly called a sea swallow, blue angel, or various other names, may well be the most exquisite creature known to mankind. It is a ocean drifter, clinging to the surface film of the sea like a snail in a pond; being a species of sea slug, there is not a great biological difference between the two.

The sea swallow feeds on siphonophores, jellyfish-like entities formed from masses of stinging polyps that drift in the plankton. The slug is immune to these venomous colonies, however, allowing it nearly exclusive access to siphonophores as a food source; it secretes their stinging cells (nematocysts) in its finger-like extensions as a defence. The stolen venom becomes extremely concentrated as the animal grows larger, giving them a stinging power agonising to humans.


No photo can really do this animal justice, but I found this particularly good one on Sylke Rohrlach’s Flickr page. Her photographs of marine life are stunning, and well worth an extended look: