GLAUCUS ATLANTICUS is a specialist predator of siphonophores, jellyfish-like creatures such as the Portuguese Man o’ War which float near the surface of the ocean and are often herded into large groups by the currents. G. Atlantici spend their lives floating amongst these aggregations, periodically gulping bubbles of gas into their stomachs to maintain buoyancy, and clinging to the surface tension with their muscular feet.

Siphonophores, like jellyfish, use venomous stinging cells (called nematocysts; VIDEO) to capture prey and defend themselves against predators. G. Atlanticus, however, is immune to nematocysts and consumes them without harm. The inside of their mouths and esophagi are lined with a hard cuticle (made of chitin) which acts to absorb the impact of discharging nematocysts and keep the underlying muscle tissue safe.  Additional protection comes from specialized mucus that inhibits nematocyst discharge by interfering with the trigger mechanism.

G. Atlanticus’s domination of nematocysts does not stop at neutralization. Unfired nematocysts pass through the digestive system undamaged and eventually become incorporated into the body as fully functioning defensive weapons. Intestinal protuberances guide nematocysts to G. Atlanticus’s rayed appendages where they are absorbed into muscularized chambers at the tips. Here they are nourished and stored, ready to be squeezed out if their new body comes under attack. A lifetime of meals concentrates powerful nematocysts from dozens of individual siphonophores, making the sting of G. Atlanticus a very potent cocktail.

Glaucus Atlanticus is a nudibranch (or sea slug), a gastropod mollusk closely related to marine snails. They drift with the currents in tropical and temperate oceans throughout the world. Their bodies measure between 3-5cm in length and possess 3 pairs of appendages that fan out into rayed cerata. Small chemosensory tentacles (called rhinophores) located on either side of the mouth help them find food, and they feed by using a toothed tongue (called a radula) to scrap and tear flesh from prey. They are short lived, typically spending their entire lives within a particular cluster of siphonophores. Like other nudibranchs, G. Atlanticus is hemaphroditic, possessing both male and female reproductive organs. After mating, which is reciprocal, both slugs lay egg strings, often on the bodies of their victims to endow their offspring with nourishment.


Valdes A, Orso A C (2004) Systematics of pelagic aeolid nudibranchs of the family glaucidae (mollusk, gastropod). Bulletin of Marine Science 75(3):381-389.

Greenwood P G (2009) Acquisition and use of nematocysts by cnidarian predators. Toxicon 54:1065:1070.

Photo Credits. 1. Richard Ververs. 2. Paulhypnos. 3. Doubtful Guest. 4. DYimages. 5. ? 6. ? 7. Atlas Zoologique du Voyage de la corvette La Bonite. Paris, Arthus Bertrand, Editeur, 1841.

Video Credits. 1. Killer Jellyfish. Australian Natural History Unit.

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