Blue Glaucus | Oceana
Home / Blue Glaucus
Marine Life Encyclopedia > Corals and Other Invertebrates > Blue Glaucus

Blue Glaucus

Don’t be fooled by its size — this tiny sea slug is as fierce as it is beautiful. The blue glaucus, also known as the blue dragon, sea swallow, or blue angel, floats upside down at the ocean’s surface, showing off its electric blue underside while feeding on venomous prey. 

 

Measuring about 2.5 centimeters (1 inch) long, the blue glaucus is a species of nudibranch, a group of soft-bodied, shell-less marine gastropods. Found throughout the Atlantic, Pacific, and Indian Oceans in tropical and subtropical waters, they spend most of their lives floating upside-down at the surface, staying afloat by storing air bubbles in their stomach. 

The bright colors of the blue glaucus are an example of a phenomenon called countershading. Its bright blue underside helps the blue glaucus blend into the water’s surface while its grayish backside helps it blend into the ocean when spotted from below, camouflaging it from both flying and swimming predators while floating in open water. But these nudibranchs don’t just depend on camouflage for protection. By feeding on venomous prey, including Portuguese man-o’-war, and ingesting their prey’s stinging cells, the blue glaucus becomes toxic itself. 

 

 

Due to the blue glaucus’s small size and its wide range around the world, little is known about its conservation status. However, like all ocean animals, they depend on healthy, clean, abundant oceans to survive.

 

 

Protecting and restoring our oceans benefits wildlife around the world. By speaking up and working together, we can create real, measurable change for oceans and marine life. Learn more about Oceana’s campaigns to protect and restore marine biodiversity and abundance here.

 

 

  • Churchill CKC, Valdés A and Ó Foighil D. (2014) Afro-Eurasia and the Americas present barriers to gene flow for the cosmopolitan neustonic nudibranch Glaucus atlanticus. Mar Biol 161: 899–910. https://doi.org/10.1007/s00227-014-2389-7 
  • Churchill CKC, Valdés Á and Ó Foighil D. (2014) Molecular and morphological systematics of neustonic nudibranchs (Mollusca : Gastropoda : Glaucidae : Glaucus), with descriptions of three new cryptic species. Invertebrate Systematics 28: 174–195. http://dx.doi.org/10.1071/IS13038 
  • Helm R. (2021) Natural history of neustonic animals in the Sargasso Sea:reproduction, predation, and behavior of Glaucus atlanticus, Velella velella, and Janthina spp. Marine Biodiversity 51: 99. https://doi.org/10.1007/s12526-021-01233-5 
  • Hernández L, Munguia-Vega A, Pérez-Alarcón, F, Fernández-Rivera Melo, F and Angulo O. (2018) Occurrence of Glaucus atlanticus in the Midriff Islands Region, Gulf of California, Mexico. American Malacological Bulletin 36: 145-149. 10.4003/006.036.0113. 
  • Pinotti RM, Bom FC, and Muxagata E. (2019) On the occurence and ecology of Glaucus atlanticus Forster, 1777 (Nollusca: Nudibranchia) along the Southwestern Atlantic coast. Anais da Academia Brasileira de Ciências 91. https://doi.org/10.1590/0001-3765201920180154 

 

GET INVOLVED

DONATE TODAY

SUPPORT OUR WORK TO PROTECT THE OCEANS BY GIVING TODAY

With the support of more than 1 million activists like you, we have already protected over 4 million square miles of ocean.

DONATE

TAKE ACTION NOW

SUPPORT POLICY CHANGE FOR THE OCEANS

Decision-makers need to hear from ocean lovers like you. Make your voice heard!

ACT NOW

VISIT OUR ADOPTION CENTER

SYMBOLICALLY ADOPT AN ANIMAL TODAY

Visit our online store to see all the ocean animals you can symbolically adopt, either for yourself or as a gift for someone else.

SHOP THE STORE

DOWNLOAD OCEAN ACTIVITIES

HELP KIDS DISCOVER OUR BLUE PLANET

Our free KELP (Kids Environmental Lesson Plans) empower children to learn about and protect our oceans!

LEARN MORE

FEATURED CAMPAIGN

Save the Oceans, Feed the World

We are restoring the world’s wild fish populations to serve as a sustainable source of protein for people.

Learn More

MORE CAMPAIGNS

Protect Habitat

Bycatch

Plastics

View All

CONTACT

Oceana International Headquarters
1025 Connecticut Avenue NW, Suite 200
Washington, DC 20036 USA

General Inquiries
+1(202)-833-3900
info@oceana.org

Donation Inquiries
+1(202)-569-4895
wavemaker@oceana.org

Press Inquiries
+1(202)-833-3900
press@oceana.org

OCEANA'S EFFICIENCY

BECOME A WAVEMAKER

Sign up today to get weekly updates and action alerts from Oceana.

SHOW YOUR SUPPORT WITH A DONATION

We have already protected over 4 million square miles of ocean and innumerable sea life - but there is still more to be done.

Donate Now

QUICK LINKS: