This tiny nudibranch goes by many names; sea swallow, blue angle, blue sea slug, and, perhaps the most theatrical and maybe most fitting, blue dragon. It’s no surprise that such an ornate creature has a plethora of identities, each hoping to capture a little of the organism’s intrigue. This wonderful little dragon is known by scientists by its latin name; Glaucus atlanticus and occurs throughout the world’s oceans.

A whole case of these little critters arrived at the aquarium a few days ago and I got the chance to observe them firsthand milling about in a light current, their bodies reminiscent of a confectioner’s gummy candy. I realized then

bermudas marine life sterrer
Wolfgang Sterrer’s comprehensive book

that I knew little about them; the other place I had seen them was on the cover of Wolfgang Sterrer’s book, and in videos proclaiming them as a “real life pokemon.” It’s hard to know how these little organisms live; they have no visible eyes or mouths, and almost appear to be little toys rather than living things.

How could I know so little about such a fascinating creature? If you look them up, Wikipedia will tell you that Glaucus atlanticus is “a species of small, blue sea slug, a pelagic aeolid nudibranch, a shell-less gastropod mollusk in the family Glaucidae.” This definition, full of scientific jargon, does little to classify them in the mind. So what exactly is an aeolid nudibranch? And what is the real essence of this creature behind all its biology?

For starters, a nudibranch simply means “naked lung” – all members of nudibranchia are classified so because they have external lungs; the atrium of their heart is posterior to the ventricle. Members of this group are known colloquially as sea slugs and include members like the sea hare (Aplysia dactylomela), the zebra slug (Hypselodoris zebra), and our blue Glaucus. Aeolid nudibranchs are nudibranchs that utilize the wind, as their name (from Aeolus, the Greek god of wind) suggests. Specifically, the blue Glaucus floats upside down, using the surface tension of the water and a gas-filled sac in their stomach to stay up, and are carried along by winds and ocean currents.

A zebra slug just chillin’

Also like most nudibranchs, the Glaucus possesses both male and female reproductive organs. Because they float, the Glaucus mates with ventral sides facing rather than with right sides facing, like other nudibranchs, and afterwards both animals produce a fertile string of eggs.

As with most pelagic (traveling over the open ocean) organisms, the blue glaucus is camouflaged by counter shading with its blue side blending in with the blue of the ocean from above and its silvery side camouflaging it against the sunny surface from predators below. It seems almost unnecessary to have this camouflage as the nudibranch won’t reach larger than 3cm long.

Glaucus, like all nudibranchs, is a vicious carnivore, feeding on other pelagic creatures like the by-the-wind-sailor (Velella velella), violet snail (Janthina janthina), and, astonishingly, the portuguese man o’ war (Porpita porpita). The Glaucus is immune to these organisms’ stinging cells, and after consumption appears to store their most venomous cells for their own use. This venom is then concentrated, meaning they can produce a more potent sting than even the man o’ war. The nematocysts are stored in sacs in the tips of the cerata, the finger/feather-like appendages of the Glaucus.

Blue Glaucus attacking a (much larger) Man o’ War

In short, the Glaucus is a tiny dragon/angel/sea slug unbound by gender roles and capable of producing a sting that would make any grown person cry. Can you think of a better sea creature? (and the mantis shrimp doesn’t count – you got it from that Oatmeal comic).

P.S: interestingly, just after I saw these guys at the aquarium, I was made aware of a Bermudian’s facebook post who spotted some at our very own Spittal Pond – and he might have been the one to bring them into the aquarium in the first place.