Species: Glaucus atlanticus
The other day, I got a strange text from my dad talking about an article that he found on the Internet describing a blue dragon that had washed up in Texas. He seemed really excited to show me the article because he thought I could blog about it. Well, “blue dragon” didn’t ring any bells, and I thought that it might have been an oarfish, which is dragon-esque. Instead, what I found is a nudibranch, most commonly known as a sea slug.
Glaucus atlanticus goes by many common names: blue glaucus, blue dragon, sea swallow, and blue sea slug, to name a few. No, it does not look like any slug you might have seen or land.
The creature has what looks like a head and a tail. Along its body are three pairs of fan-like appendages that look like wings. The blue sea slug can grow up to 1.2 inches (3cm) in length, which would make it the smallest dragon in the Guinness World Record book. However, it is not the smallest sea slug!
Most sea slugs live on the seafloor. They can live on coral, or the sandy substrate, or even rocky surfaces. Glaucus atlanticus isn’t like its cousins, though. Instead, they are a pelagic sea slug, meaning they live in the open water column. They have been sighted more often up towards the ocean’s surface.
The blue sea slug floats in the water column by storing an air bubble in its body, acting like an air bladder in fish. If it hangs out near the surface, how does it hide from sea birds?
Glaucus atlanticus has a special coloration that allows it to blend into its surroundings called countershading. The blue sea slug floats on its backside, showing the bright blue underbelly toward the sky. The blue helps it blend into the waves and makes it hard for sea birds to see the creature. On the other side, it is a grayish color that blends in with the surface water from below, making it nearly invisible to its underwater predators.
Countershading isn’t the only defense it has against predators. In fact, like most sea slugs, this is a creature you don’t want to touch—no matter how pretty it looks!
One of the things blue dragons consume is the Portuguese man o’ war, a type of hydrozoan known to give nasty stings to beach-goers. The Portuguese man o’ war has long tentacles, almost 30 feet long, which are full of stinging cells.
When the blue dragon consumes the Portuguese man o’ war it stores the hydrozoan’s stinging cells in those fan-like appendages. When a diver or predator gets too close, the blue dragon will brush up against the perceived threat and sting them with the stinging cells. It’s been reported that a sting from a Glaucus atlanticus hurts more than a sting from a Portuguese man o’ war—so watch out for these critters when swimming! They’re found in the warm waters of the Pacific, Indian, and Atlantic Oceans.
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Sources and links:
Reef Creature Identification: Florida, Caibbean, Bahamas 3rd edition by Paul Humann, Ned Deloach, and Les Wilk
https://scubadiverlife.com/marine-species-glaucus-atlanticus/ ⇐has dive-related news articles as well