This post is part of a 4-part series by students of a Biological Oceanography course at Pennsylvania State University taught by Dr. Mónica Medina.
When you think of a dragon, does a simple sea slug come to mind? A dragon and a slug may seem as unrelated as possible, but in comes Glaucus Atlanticus, what some people call the Blue Dragon. This interesting creature has been mistaken for many different things due to its color patterns and six arms- including a sea insect and even a larval stage of an angel shark. In fact, it is a marine snail (phylum Mollusca, class Gastropoda), part of the group Nudibranchia, which lack shells as adults. Glaucus stores an air bubble inside its stomach and floats along the sea surface, belly side up, and just goes where the current takes it. This beautiful, tiny slug seems innocent enough but be careful if you pick one up, you may be in for an unpleasant surprise.
This beautiful creature that is only about three centimeters long can live up to a year under the right conditions. Its bright belly and grey back help camouflage the tiny creature from predators both above and below it. Hiding from predators, though, is not how the Blue Dragon got its name. Stored in the feather like arms, or cerata, along the slug’s body are nematocysts filled with dangerous venom. The Dragon doesn’t produce its own nematocysts though; it steals them from the Portuguese Man-o-War (Physalia physalis), another beautiful yet dangerous creature of the sea. The slug will clamp down on the Man-o-War and start ripping off chunks using its radula, a tooth like scraper. As the sluf consumes the nematocysts, which are capsular organelles present in all cnidarians, it does not get stung. Instead, its body is able to process the stingers without setting them off and move them through its digestive tract out into its cerata to be used as defense. Because it is storing the venom from many other creatures, the sting from the Blue Dragon can be more painful and serious than the string from the Man-o-War. This slug also has a strong jaw and denticles that allow it to clamp down on larger prey while tearing away the pieces and eating the animal. Dragon is beginning to make sense. Blue dragons may even turn to cannibalism, taking down one of its own kind if food is scarce.
Another fascinating feature about the Blue Dragon is that they are hermaphrodites, meaning that all individuals contain both male and female reproductive organs. The male reproductive organ has evolved to be especially large and hooked so that it can safely penetrate the female without being affected by the venomous cerata. So once mating takes place, both individuals are able to lay eggs. Each female reproductive organ will release an egg string. With each egg string containing about 20 eggs. Even though these slugs don’t stay around and take care of their young, they are careful about where they lay the eggs. Most popular spots include wood pieces, carcasses or any other floating objects that provide the newborn slugs with time to develop their own air sacs before setting off into the water.
The many interesting adaptations of Glaucus atlanticus make the beautiful Blue Sea Dragon one of the most interesting species in the ocean. More research on them is likely to make them even more fascinating. Indeed, Jessica Goodheart, a PhD student associated with the department of Invertebrate Zoology is studying the evolution of this group of sea slugs.
by Heli Bhatt and Andrea Befumo
love this animal i would love to see one on real world
Posted by: Erick Savana | 01 February 2019 at 02:47 PM
are they classed as a living fossil
Posted by: quillan | 24 August 2018 at 03:49 PM
This was really helpful, with a project I had for school
Posted by: Micah | 20 April 2017 at 07:07 PM