Sunday 11 March 2018

Mud Dragon

Image: WoRMS Editorial Board
From the sounds of it, this must surely be the lowliest of all dragons. Fire dragons soar overhead, frost dragons slumber in beautiful ice lairs, swamp dragons brood in their stinking miasmas, even flightless flu dragons get to lie in bed all day.

What do poor old Mud Dragons get? They get to wriggle. In the mud. Hmmm... Someone drew a very short straw.

Image: Alvaro Esteves Migotto
Mud Dragons are some 150 species which make up their own phylum called Kinorhyncha. There are only 35 animal phyla in the world, maybe one or two less depending on who you ask, and they're pretty much all insects. This despite the fact insects are just one part of the arthropod phylum. Look at the other three dozen phyla and you'll find flat things called Strange Worms, hairy things called mammals, things found only on lobsters called Cycliophora, and dragons that seldom grow more than a millimetre in length.

Yup, Mud Dragons are that teeny-tiny! I wasn't joking about how short that straw was. And in contrast to other dragons— the ones with splendid wings, vicious claws, sinuous tails and lairs full of gold—your average Mud Dragon looks like a microscopic grain of rice.

Image: Brandon C
At least the Mud part is accurate. Mostly. Mud Dragons live in sand and mud, usually in the ocean, though a few species live in brackish estuaries. There are also Mud Dragons who prefer a more lively environment. 'Lively' as in alive. They're found scratching a living on algae mats, sponges or bryozoans.

When it comes to the essentials of life, Mud Dragons are easily pleased. They can be found everywhere from the intertidal zone all the way down to the most abyssal of depths, over 5,000 metres (16,500 ft) down. Don't fret if a Mud Dragon pays you a visit, they are a most undemanding guest who can do perfectly well without fine dining, pleasurable diversions or even light. I'm not saying they'd turn their nose up at a freshly oiled maiden, I'm just saying it's not a requirement.

Video: Matthew Lee

The Mud Dragon's closest relatives are our old friends the Penis Worms. It's important to note that even the smallest Penis Worms are considerably larger than Mud Dragons. I suspect this mostly tells us they were both named by men.

Being so closely related, Mud Dragons and Penis Worms bear various similarities. They're both simple creatures with very simple nervous systems and scant few internal or external organs. Some Mud Dragons have simple eyes to tell light from dark, other species don't even bother with that much. They learn about the outside world predominantly through touching it with the sensory bristles that cover their body. Sounds a bit like being buried alive to me but then I'm not a dragon. You can tell from all the pleasurable diversions I need.

Image: Martin V. Sørensen
Unlike Penis Worms, Mud Dragons are segmented. An adult's body is composed of precisely thirteen segments: one for the head, one for the neck and eleven for the rest of the body.

Those sensory bristles are cool and all but they pale into insignificance compared to the face-spines. The single most dragonish things Mud Dragons have in their possession are those spines and their importance goes beyond self-esteem, Mud Dragons also use them to move through their surroundings.

Mud Dragons have up to seven rows of spines encircling their head. Like Penis Worms, that head is an introvert, which means it can be completely retracted into their neck. So, Mud Dragons get around by stretching out their head and using the spines as grappling hooks to gain purchase on the sand around them. Then they drag their whole body forward by retracting their head. This is where they get their scientific name from—Kinorhyncha means something like "move snout."

There's a lot yet to be learned about Mud Dragons. For a start, we don't know much about how they feed, though they probably eat single-celled algae and other microscopic specks of detritus.

Image: Rick Hochberg
Little is known about how they reproduce, either. They do lay eggs, though, which hatch into even tinier versions of the adults. Hatchlings already have eleven segments and they moult several times, eventually acquiring two new segments to add to the collection.

Dragons, eh? Always keeping their secrets close their scaly chests, and Mud Dragons are even more secretive than the others. They were first discovered as recently as 1841, so while people like St George were slaying all the charismatic megadragons, no one had any idea of the millions of microscopic ones hiding in the mud. Who drew the short straw now?

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