Blue Glaucus - Oceana

Marine Life Encyclopedia

Corals and Other Invertebrates

Blue Glaucus

Glaucus atlanticus

Distribution

Atlantic, Pacific and Indian Oceans

eCOSYSTEM/HABITAT

Open ocean

FEEDING HABITS

Foraging predator

TAXONOMY

Order Nudibranchia, Family Glaucidae

 

The blue glaucus, which is also called the blue dragon, sea swallow, or blue angel, is a brightly colored nudibranch, commonly known as sea slugs.  Found throughout the Atlantic, Pacific, and Indian Oceans in tropical and subtropical waters, the blue glaucus grows up to 1.2 inches (3 cm) long. These tiny sea slugs 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. A group of blue glaucuses floating together is called a “blue fleet.” These “blue fleets” often wash ashore and can sting people swimming in the water.

The blue glaucus is a simultaneous hermaphrodite — each individual has both male and female reproductive organs. After a pair mates, they will lay a string of about 16 eggs in the water which take about three days to hatch into larvae. Due to the blue glaucus’s small size and its wide range around the world, little is known about its conservation status.

 

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