Glaucus atlanticus (blue sea slug)

These little guys are pretty awesome. They live in temperate and tropical waters, staying afloat by swallowing air and keeping it in their stomachs. They eat the venomous Portuguese Man o’ War jellyfish and keep its stings for their own defence. And they look like cycloptic alien dragons. What’s not to love?

(Photos and info from Wikipedia, the Natural History Museum and Animals Talking in All Caps.)

Edited to add: Here’s what they look like on the inside!

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 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?

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)