Blue Dragon Sea Slug

Glaucus atlanticus

Last updated: May 27, 2024
Verified by: AZ Animals Staff
© iStock.com/S.Rohrlach

They steal the venomous nematocysts from their prey and concentrate the venom in their own bodies!


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Blue Dragon Sea Slug Scientific Classification

Kingdom
Animalia
Phylum
Mollusca
Class
Gastropoda
Order
Nudibranchia
Family
Galucidae
Genus
Glaucus
Scientific Name
Glaucus atlanticus

Read our Complete Guide to Classification of Animals.

Blue Dragon Sea Slug Conservation Status


Blue Dragon Sea Slug Facts

Main Prey
Portuguese man o' war
Name Of Young
Veliger
Group Behavior
  • Solitary
Fun Fact
They steal the venomous nematocysts from their prey and concentrate the venom in their own bodies!
Biggest Threat
Pollution
Most Distinctive Feature
Blue and silver coloration
Distinctive Feature
Coloration, venom, cerata
Other Name(s)
Blue glaucus, sea swallow, blue sea dragon, blue dragon, dragon slug, blue angel, blue sea slug, blue ocean slug
Predators
Loggerhead turtle
Common Name
Blue glaucus
Number Of Species
1
Slogan
They inflict a painful, venomous sting
Group
Blue fleet

Blue Dragon Sea Slug Physical Characteristics

Color
  • Blue
  • Silver
  • Light Grey
Skin Type
Smooth
Venomous
Yes
Aggression
Medium

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The blue dragon sea slug is a shell-less marine gastropod mollusk remarkable for its vibrant blue coloration. It ranges throughout temperate and tropical areas of the Atlantic, Pacific, and Indian Oceans. Because it floats in open waters, it often washes up in unexpected places, soon dying. This venomous species is known for its painful and dangerous stings, the result of stinging nematocysts stored in the tips of its cerata.

5 Blue Dragon Sea Slug Facts

  • Venomous sting: This species is famous for its venomous sting, which is both extremely painful and potentially dangerous. Despite not being venomous on its own, it incorporates the stinging nematocysts of its prey.
  • Branching cerata: Part of this species’ visual appeal is its finger-like cerata, which branch out from its body in three pairs. These cerata store venomous stingers at their extreme tips.
  • A stunning shade of blue: This sea slug is gorgeous to look at with its vibrant dark and light blue color. Its countershading is reversed with its back being lighter and its belly being darker. This developed due to its habit of floating on its back.
  • Floats on its back: This species has evolved to float near the surface of the water by storing an air bubble in its stomach. The position of the air bubble causes it to float with its belly toward the sky.
  • Eats prey much larger than itself: These sea slugs are voracious eaters that prey on animals much bigger than themselves. This includes the highly venomous Portuguese man o’ war, its preferred meal.
Blue dragon sea slug rarely exceeds 1.2 inches

The blue dragon sea slug rarely exceeds 1.2 inches in length.

©iStock.com/S.Rohrlach

Blue Dragon Sea Slug Classification and Scientific Name

The scientific name for the blue dragon sea slug is Glaucus atlanticus. Alternate names for this species include blue glaucus, sea swallow, blue sea dragon, blue dragon, dragon slug, blue angel, blue sea slug, and blue ocean slug. It shares its genus Glaucus with four other species. Scientists once considered Glaucus marginatus to be the only other species besides G. atlanticus in the genus; today, they consider it to be a cryptic species complex including four species, namely:

  • Glaucus bennettae
  • Glaucus marginatus
  • Glaucus mcfarlanei
  • Glaucus thompsoni

The genus Glaucus is the only one within the family Glaucidae. It also falls within the superfamily Aeolidioidea (aeolid nudibranchs) and the order Nudibranchia (nudibranchs). Blue dragons further belong to the class Gastropoda (slugs and snails) and the phylum Mollusca (mollusks).

Blue Dragon Sea Slug Appearance

The blue dragon sea slug, Glaucus atlanticus, often floats upside down

Because the blue dragon sea slug often floats upside down due to an air bubble in its stomach, its belly is darker than its back.

©iStock.com/S.Rohrlach

The blue dragon is remarkable for its stunning coloration. Its dorsal region is silvery-grey while its ventral region is dark and pale blue. Dark blue stripes mark its head. Typically, species using countershading as a camouflage technique are darker on their backs (to blend into the water from above) and lighter on their bellies (to blend into the sky from below). Because Glaucus atlanticus often floats upside down due to an air bubble in its stomach, its belly is darker than its back.

These sea slugs are also remarkable for their cerata, which extend from three pairs of peduncles. Cerata are structures that aid in respiration, digestion, and attack or defense. They contain cnidosacs at their tips, which themselves contain stinging cells called cnidocytes. In addition to this adaptation, Glaucus atlanticus possesses serrated radular teeth useful for grasping and shredding the flesh of its prey.

This species rarely exceeds 1.2 inches in length, though some individuals have grown as long as 1.6 inches. It weighs between 0.1 and 3.5 ounces.

Blue Dragon Sea Slug Distribution, Population, and Habitat

The blue dragon occurs throughout temperate and tropical areas of the Atlantic, Pacific, and Indian Oceans. It is a pelagic species, floating in open waters and drifting according to the currents and wind direction. Because of this, it often washes ashore where it then dies. It occurs at depths up to 120 feet.

Observers have noted this species off the coasts of certain countries within North America, South America, Africa, Asia, Oceania, and even Europe. Within the United States, blue dragons have even washed up on the shores of Texas in the Gulf of Mexico. Countries, islands, and regions with this species include the following:

North AmericaSouth AmericaEuropeAfricaAsiaOceania
ArubaBrazilPortugalCape VerdeIndiaAustralia
BarbadosChile MozambiqueTaiwanKermadec Islands
BermudaPeru South AfricaVietnamNew Zealand
Canada    Pitcairn Islands
Hawaii     
Jamaica     
Mexico
Panama     
United States     

The total population of blue dragons is unknown. The IUCN does not currently include this species on its Red List.

Blue Dragon Sea Slug Evolution and History

Among gastropods, nudibranchs like Glaucus atlanticus are notoriously sparse in the fossil record. This is due to their boneless and shell-less soft bodies, which do not fossilize well. On the other hand, the fossil record has amply preserved the history of shelled gastropods from the earliest Paleozoic Era (541 to 252 million years ago). Among those of other classes, Gastropoda fossils appeared during the Cambrian Period (541 to 485.4 million years ago).

Nudibranchs evolved their unshelled form over time in concurrence with or following other protective adaptations. These adaptations include the use of chemicals from prey as a defensive mechanism. In the case of G. atlanticus, its ability to take on the venomous nematocysts of its prey is essential to its survival due to the lack of a protective shell.

Blue Dragon Sea Slug Predators and Prey

Blue dragons are carnivores that incorporate the stinging nematocysts of their prey into their own bodies. They store them in their cerata for later use.

What Do Blue Dragon Sea Slugs Eat?

The blue dragon sea slug preys on Portuguese man O' war

The blue dragon sea slug’s main prey is the dangerously venomous Portuguese man o’ war

.

©iStock.com/aldorado10

This species is notable for feeding on prey much larger than itself. Its main prey is the dangerously venomous Portuguese man o’ war (Physalia physalis), a pelagic siphonophore with stinging tentacles. It consumes the tentacles, concentrating them to deliver a far more potent sting. It also preys on species like the by-the-wind sailor (Velella velella), the blue button (Porpita porpita), and the violet snail (Janthina janthina). In addition to this, it is cannibalistic, occasionally feeding on members of its own species.

What Eats Blue Dragon Sea Slugs?

Though little is known about this species’ predators, scientists speculate that the loggerhead turtle (Caretta caretta) may be among them. It is reasonable to assume that many potential predators avoid the blue dragon due to its venomous sting.

Blue Dragon Sea Slug Reproduction and Lifespan

Blue dragon sea slugs are simultaneous hermaphrodites, meaning each individual has both male and female sex organs at the same time. Despite this, they cannot fertilize their own eggs and must rely on a second individual to act as the male. Blue dragons have evolved their male reproductive organs in a hook shape to avoid their partner’s stinging cerata.

Once fertilization has occurred, both individuals release strings of between 12 and 20 eggs each, laying an average of 55 strings per hour. The eggs either float or become attached to surfaces, including the carcasses of prey. They eventually hatch into larvae called “veligers.” The common term for a group of blue dragons is “blue fleet.”

This species lives as long as one month to one year.

Blue Dragon Sea Slug in Fishing and Cooking

Blue dragons are venomous and, therefore, not appropriate for human consumption. They may occur as bycatch, in which case fishermen should exercise caution when handling them. Certain other species of nudibranchs may be edible depending on what they eat. The term “sea slug” may also apply to sea cucumbers, which are commonly included in cuisine worldwide.

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About the Author

Kathryn Dueck is a writer at A-Z Animals where her primary focus is on wildlife, dogs, and geography. Kathryn holds a Bachelor’s Degree in Biblical and Theological Studies, which she earned in 2023. In addition to volunteering at an animal shelter, Kathryn has worked for several months as a trainee dog groomer. A resident of Manitoba, Canada, Kathryn loves playing with her dog, writing fiction, and hiking.

Blue Dragon Sea Slug FAQs (Frequently Asked Questions) 

Where are blue dragon sea slugs found?

Blue dragons occur throughout temperate and tropical areas of the Atlantic, Pacific, and Indian Oceans. They are pelagic, floating near the surface of the water.

How do you identify blue dragon sea slugs?

Blue dragons are dark and light blue on their bellies and silvery-grey on their backs. They have three pairs of branching, finger-like cerata. This species rarely exceeds 1.2 inches in length, though some individuals have grown as long as 1.6 inches.

Do blue dragon sea slugs sting?

Blue dragons administer painful, potentially dangerous stings to both prey and predators.

Are blue dragon sea slugs venomous?

Although they are not venomous on their own, blue dragons ingest the stinging nematocysts of their prey for use in their own defense. In humans, the venom from these nematocysts results in symptoms like nausea, vomiting, and intense pain.

Can you eat blue dragon sea slugs?

Blue dragons are not appropriate for human consumption.

Are blue dragon sea slugs endangered?

The IUCN does not currently include this species on its Red List. The total population of blue dragons is unknown.

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Sources