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Glaucus atlanticus: The Blue Dragon 1 DSC_5634

Blue Dragon / Sea Lizard - NSW, AUSTRALIA. with Porpita porpita on the right.

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"Glaucus atlanticus Forster, 1777




This is a bluish-purple nudibranch with a white underside. It resembles most nudibranchs. The elongated, flattened body is up to 3 cm long. The papillae (up to 84 in number) are placed in four or three pairs of clusters (Glaucus atlanticus). It lives in the pleuston of all oceans.


Taxonomic Description


The naked body is elongate and flat. The head is small and blunt. It has a pair of small oral tentacles near the mouth and a pair of extremely small rhinophores on the dorsal side. There are four or three pairs of clusters of papillae (cerata) placed on peduncles on the lateral side of the body. The papillae are placed in a single row (uniseriate), their may be 84 in total. The genital pore is on the ventral side at the right; the renal pore is on the right dorsal side between the first and second cluster of papillae; the anus is dorso-laterally at the right between the second and third pair of papillae. The penis is armed with a chitinous spine. The foot is flat and slender, at the ventral side; the metapodium is long. The body is deep bluish-purple ventrally (= upperside in living animals) the dorsal side is silvery white. The radula formula is 0-1-0 (Glaucus atlanticus radula).

Body length up to 43 mm.




A special description is not available.




This species is hermaphroditic. The eggs are 60-75 µm wide and 75-97 µm long. Eggs are laid in straight strings up to 17.5 mm long. At 19°C, division of the eggs starts after some hours. After 48-60 hours a trochophore is formed and after three days a veliger with larval shell (first ovoid, is coiled at the day 11 after hatching) leaves the egg string.




This species is carnivorous and lives in the pleuston where it feeds on Velella, Porpita and Physalia. The nematocysts of Physalia pass unharmed through the digestive system and are used as defence system in the papillae, this is an example of oplophagia (Donati and Porfirio (1986).


Practical Importance


As this species can use the stinging nematocysts of its prey animals it can be harmful to humans.




This species occurs in the tropical waters of all oceans, see the Glaucus atlanticus map." ref:


We have a little cabin on a cliff by the sea. We listened to the storm all night as the waves crashed on the rocks below us. The next morning many ocean drifters had been washed onto the sand and into rock pools.


I spent the morning photographing these amazing animals.


The animal above can eat the stinging cells of other sea creatures and secrete them into special sac at the tip of their cerata. People who picked them up were stung severely. (See below)


This was a morning I will always remember.


In January 2011 we found one beautiful specimen of this creature again and released it into the ocean.


“ A day in such serene enjoyment spent,

Is worth an age of splendid discontent.”

Moliere (pseudonym of Jean Baptiste Poquelin), Tartuffe (act IV, sc. 5)


This nudibranchs feeds almost exclusively on Physalia, it appears that they are able to select the most venomous of Physalia's stinging nematocysts for their own use. Like most aeolids, they store the nematocysts in special sacs (cnidosacs) at the tip of their cerata .


Glaucus atlanticus is a species of medium-sized, floating, blue sea slug, a pelagic aeolid nudibranch, a marine opisthobranch gastropod mollusk in the family Glaucidae

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Taken on January 3, 2011