LAST DRAGON IN WORLD

“Blue Dragon” Sea Slug Reminds Us That the Ocean is Filled With Strange Creatures That Look Like Pokemon

The strange blue creature in the photo above may look like a monster from a Japanese RPG, but is actually a  real animal—the Glaucus atlanticus sea slug, to be exact.

Commonly known as the blue dragon or blue sea slug, this beautiful little mollusk can be found off the coast of South Africa, Australia and Mozambique, floating on the surface tension of the water.

Glaucus atlanticus got quite a bit of attention on the internet in April after a stunning up-close photo was posted to imigur (above). While we only just stumbled upon the blue dragon today, the moment we saw it we had the feeling this wasn’t the first time we had seen a sea slug that looked like something out of a fantasy world.

Glaucus atlanticus (common names sea swallow, blue glaucus, blue dragon, blue sea slug and blue ocean slug) sea slug, apelagic aeolid nudibranch, a marine gastropod mollusk in the family Glaucidae. This is the o

Description

The regular size of this species is up to about 3 cm,depending on the animal's age.^[3] It is silvery grey on its dorsal side and dark and pale blue ventrally. It has dark blue stripes on its face. It has a tapering body which is flattened and has six appendages which branch out into rayed cerata.^[4] Its radula bears serrated teeth on their blades.^[5]

Glaucus atlanticus and its close relative, Glaucilla marginata, live in close association with what Sir Alistair Hardy described many years ago as "The Blue Fleet" - the siphonophores such as Physalia physalis, Velella velella, Porpita porpita and the other associated animals including the "violet snails" of the genus Janthina. All these animals float on the surface of the ocean being carried by the currents and the winds. Most of us are only aware of their existence when days of onshore winds blow great fleets of them on to the beaches, causing pain and angst for swimmers.

Both species spend their life floating upside down in the water, partially bouyed by a gas bubble in their stomachs.

The two nudibranchs feed almost exclusively on Physalia, and as Tom Thompson and Isobel Bennett reported some years ago, 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 .

There are a number of reports in Australia of kids engaged in "Bluebottle" fights - where they throw stranded Physalia at each other - being badly stung by inadvertently playing with Glaucus and Glaucilla, both of which, by concentrating the most venomous of Physalia's nematocysts, are much more deadly.

Another interesting feature of the two species is their colouration. They both exhibit a textbook example of colour countershading. Their foot and undersides of the cerata, (which because they float upside down is effectively their dorsal surface), is blue or blue and white which helps to camouflage them from predation (sea birds) from above. Their true dorsal surface, which faces down in the water, is silvery grey to effectively camouflage them from fish looking up from below.                                                                                        

Distribution and habitat 

This nudibranch is pelagic, and is distributed throughout the world's oceans, in temperate and tropical waters. Regions where this slug is found include the East and South Coast ofSouth Africa, European waters, the east coast of Australia and Mozambique. And has been seen, too, in some regions of <<Costa Rica>> ^[6] This species floats upside down on the surface tension of the ocean.

Life history and behavior

G. atlanticus preys on other, larger pelagic organisms: the dangerously venomous Portuguese Man o' War Physalia physalis; the by-the-wind-sailor Velella velella; the blue buttonPorpita porpita; and the violet snail, Janthina janthina. Occasionally, individual Glaucus become cannibals given the opportunity.

G. atlanticus is able to feed on P. physalis due to its immunity to the venomous nematocysts. The slug consumes the entire organism and appears to select and store the most venomous nematocysts for its own use. The venom is collected in specialized sacs (cnidosacs), on the tip of their cerata, the thin feather-like "fingers" on its body.^[7] BecauseGlaucus concentrates the venom, it can produce a more powerful and deadly sting than the Man o' War upon which it feeds.^[7]

With the aid of a gas-filled sac in its stomach, G. atlanticus floats at the surface. Due to the location of the gas sac, the sea swallow floats upside down. The upper surface, actually the foot (the underside in other snails), has either a blue or blue-white coloration. The true dorsal surface (downwards in G. atlanticus) is completely silver-grey. This coloration is an example of counter shading, which helps protect it from predators from below, sides, and above.

Like almost all heterobranchs, Glaucus is a hermaphrodite, having both male and female reproductive organs. Unlike most nudibranchs, which mate with their right sides facing, sea swallows mate with ventral sides facing.^[8] After mating, both animals produce egg strings.\