Atretochoana eiselti. Credit: Juliano Tupan

"What? What are you guys all laughing at? No, of course I don't have any idea what I look like. You're laughing because I'm so ridiculously good-looking, right? Guys? Hey stop stealing my fries, don't think I can't sense you!"


Yes, this is probably the most unfortunate-looking animal in the world, and yes that's because it looks like a penis, but what would you look like if you were blind, lungless, limbless and one metre long? While many headlines have been calling this the discovery of a "new species", we have known about the incredibly rare Atretochoana eiselti since it was first described by American herpetologist Edward Harrison Taylor in 1968 from a single 738mm-long specimen, dead and preserved in the bottle in the Naturhistorisches Museum of Vienna.

That, and Taylor's very minimal description (he didn't notice the total lack of lungs) in his monograph Caecilians of the World, was all we had of this hairless heartbreaker for the following 30 years, until herpetologists Mark Wilkinson and Ronald A. Nussbaum studied the first specimen before discovering their own bottled specimen in a collection of the University of Brasília in Brazil. This specimen, stretching 805mm, was named the largest lungless tetrapod (vertebrate animals with four limbs) on Earth and the only known lungless caecilian - a very poorly understood group of amphibians that superficially resemble earthworms or snakes.

Head in frontal view showing large mouth and sealed nostrils. Credit: A. O. Maciel

Then late last year, a group of engineers drained a hydroelectric dam in the Madeira river in Rondonia, Brazil, and noticed six A. eiselti specimens sitting on the riverbed. Brazilian biologist Juliano Tupan was brought in to investigate and later commented, “Of the six we collected, one died, three were released back into the wild and another two were kept for studies. Despite looking like snakes, they aren’t reptiles and are more closely related to salamanders and frogs ... The Amazon is a box of surprises when it comes to reptiles and amphibians. There are still much more to be discovered.”

Commonly known as 'floppy snakes', A. eiselti has a flat, widened head with two sealed, internal nostrils called choanae, and a complete lack of pulmonary arteries and veins. Lunglessness like A. eiselti's is usually restricted to small species of salamanders and a small Bornean frog called Barbourula kalimantanensis, so the fact that A. eiselti is so much larger than any of these is a real surprise. Together with its lack of open nostrils, A. eiselti's lunglessness has posed quite a problem for scientists, because no one has been able to figure out how it obtains oxygen from its watery surroundings.

Credit: RA Nussbaum, University of Michigan

What this species does have, however, are capillaries that sit very close to the skin - there's only about two or three cells between its blood and the surface of its skin, according a 2011 Boletim do Museu Paraense Emílio Goeldi paper by a team of Brazilian biologists including Tupan. What this could mean, the team suggested, is that the only way for this species to obtain oxygen from the water is through its skin: "Possibly the wrinkles in the skin serve to increase total skin surface in order to facilitate skin respiration...". This is the case in the Lake Titicaca frog (Telmatobius culeus), commonly known as the 'scrotum frog', and the hellbender salamander, or mud dog' (Cryptobranchus alleganiensis). Still, the team says, as some turtles breathe through their cloacal openings, this possibility can't be ruled out for A. eiselti. A bald butt-breather. Say it isn't so.

For more surreal caecilians, read Darren Naish's round-up.