Creature Feature: The Blue Dragon (Glaucus atlanticus)

The first time I saw a picture of this little guy I thought it had to be a photoshop thing; some little creature made up by some talented artist. It made me want to delve deeper, and you know what I found - It really does exist!

Believe it or not, this little sea slug or nudibranch, is pelagic (lives in the open water). It is often found floating upside down on the surface of the ocean in temperate and tropical waters in such regions as the east and south coasts of South Africa, Mozambique, European waters, the east coast of Australia, and the islands of Hawaii. They also have been spotted in the waters of Bermuda. Its average size when fully grown is a whopping 3-4cm. The blue dragon's floating abilities are due to a gas-filled sac located in its stomach. Because of its location, this sac causes the slug to float upside down exposing its blue-white foot to the surface of the water, leaving the silver-gray dorsal surface facing downward into the water. This is an example of counter shading, where the coloration helps to protect the organism from it predators both below and above. These slugs spend most of their lives drifting along, directed by currents and winds. They are generally not observed by humans except on those occasions when strong onshore winds bring masses of them (often called the "blue fleet") to beaches, causing much pain for swimmers and beach-goers.

Common names for this beautiful slug are blue dragon, blue glaucus, blue sea slug, blue ocean slug, and sea swallow. G. atlanticus is carnivorous and preys on other, larger pelagic organisms such as the venomous Portuguese Man o' War, the by-the-wind sailor, the blue button, and the violet snail. They have also been know to become cannibalistic.

The blue dragon is immune to the venomous nematocysts of the Portuguese Man o' War, and when consuming this animal, appears to select and store the most venomous nematocysts in specialized sacs called cnidosacs on the tip of its feather-like fingers. Because it is able to store up this venom for future use, ironically it can produce a more powerful and deadly sting than the man 'o war upon which it feeds.

Blue dragons are hermaphrodites (have both male and female reproductive organs). After mating, both animals produce 4-6 egg strings within an hour that float freely in the water or are placed on the remains of prey. These busy little slugs can produce from 3300-8900 eggs per day.

References:

1. Glaucus atlanticus Forster, 1777. World Register of Marine Species, accessed 3 April 2010.
2. "Marine Species Identification Portal : Glaucus atlanticus". Species-identification.org. http://species-identification.org/species.php?species_group=pelagic_molluscs&id=189. Retrieved 2011-11-21. 
3. Rudman, W. B. (6 November 1998). "Glaucus atlanticus Forster, 1777". Sea Slug Forum. http://www.seaslugforum.net/factsheet.cfm?base=glauatla. Retrieved 26 February 2011. 
4. Debelius, H.; Kuiter, R. H. (2007). Nudibranchs of the world. IKAN-Unterwasserarchiv. ISBN 978-3-939767-06-0. 
5. http://seaslugsofhawaii.com/species/Glaucus-atlanticus-a.html
6. http://www.thecephalopodpage.org/marineinvertebratezoology/glaucusatlanticus.html