Finding Nemo never put me on to this!
Seriously though, the Glaucus atlanticus, also known as the blue sea slug, is an animal that raises many questions. Questions like:
1. "Does it really float on its back?"
2. "How can you tell?"
3. "What does it do?"
4. "Is it poisonous?"
5. "Where does it come from?"
Let us start with the most important question of all:
"What is the Glaucus atlanticus?"
The Glaucus atlanticus is a planktonic animal that belongs to the oceanic group known as Nudibranches, that is also thought of as an "unusual" group of molluscs. Molluscs have muscular feet and rhinopores, the term for their tentacles. What is noticeably different about the Glaucus to a mollusc is that it does not have a shell. It is planktonic because it feeds off of microscopic organisms such as protozoans or algae. Think SpongeBob SquarePants. Plankton drift in large groups in salt and even fresh water. They also serve as food for larger organisms swimming in the deep blue sea.
Since the Blue Dragon (as the Glaucus is also called) is in fact planktonic, it has adapted physically to fit its needs. One adaptation is the sac located in its stomach that is filled with gas helping it stay afloat. It is probably the most important attribute that it has, considering that drifting among the ocean's waves is its only real form of transportation. The Blue Sea Slug also feeds on nematocysts (stinging cells) and the most dangerous type of them as well!
They are called Blue Bottles or, more interestingly, the Portuguese Man O' War or the By-The-Wind-Sailor. If there are not enough Blue Bottles in an area, the Blue Dragon will take to cannibalism and feed on other nearby Glaucus. It is also immune to the nematocysts, thus giving it the ability to consume them as well as store its dinner's venom for its own use! The venom is collected by the tips of the slug's feather-like "fingers" called cerata and stored in specialized sacs called cnidosacs. There are three pairs of cerata used for respiration, defense and digestion. This is why the Blue Dragon is feared more than the Blue Bottle; Glaucus can have a much deadlier sting depending on the amount of venom stored within its body.
One of the most unique things about this animal is the way it floats. Glaucus atlanticus do indeed float upside-down. Its dorsal surface (backside) is actually its "foot" and belly and is either blue or blue and white in coloration. The true dorsal surface of the Blue Dragon is a silvery-greyish color. Both colorations on each side help camouflage and protect the G. atlanticus from both underwater and aerial predators alike. Think about the color of the ocean's surface from above. It looks blue and white because of the waves, whereas underwater, darker colors like silver and grey make it harder for prey to be spotted.
Another interesting fact is that the Blue Dragon is a hermaphodite. In actuality, most sea slugs are hermaphodites, allowing both slugs to produce egg strings after mating. G. atlanticus grow to be about 40-50mm and can be found all over the world in temperate to tropical waters. Glaucus tend to lay their eggs on driftwood or even the skeletons of their prey (yuck!). They lay the eggs on objects or animals that remain afloat to allow their young to develop until they have their own air sacs. When out of water, they tend to roll into a little ball and open up again once they are placed back into water. They also flip themselves over slowly when placed in water if their silver-grey surface is facing the sky.
There is much more to learn about this strange looking creature, and more and more people are becoming aware that they exist. Hopefully, animals like these may inspire people to take interest in the world around them; you never know what you may come across on our planet Earth so keep your eyes open!