This newly rediscovered species is being touted as a “penis snake”, but it’s neither penis nor snake. It is in fact a caecilian, and since you’re interested in biology (why else are you here?), you’ll need to know a bit about them. I found, via website io9, a description of a new caecelian species that happens to be the largest tetrapod (land-dwelling vertebrate) without any lungs. This one had actually been previously described from a couple of pickled specimens, but new work has found its natural habitat and has even led to observations of them alive in the wild. (See a more informative description of caecelians at National Geographic.)
But first, what is a caecilian? Before I did a bit of digging, I’d always thought they were simply legless salamanders, but that turns out to be untrue. True, like salamanders they are carnivorous amphibians and have species that are either fully aquatic or terrestrial (but bound to moist habitat). They’re found on three continents and central America, though caecelians (of which there are 187 species) are tropical. They’re also the only group of amphibians (the order Apoda, which means “no feet”) that reproduces entirely through internal insemination.
But they are not salamanders: they constitute a monophyletic group (i.e., a group in which all modern descendants go back to one common ancestor) that split of from the ancestors of modern salamanders around 150 million years ago. They are in fact a “sister group” of salamanders. Here’s where they fall on the tetrapod family tree:
So they ain’t salamanders, but they’re close to them. Anyway, a new paper by Marinus Hoogmoed et al. (free download) from Bol. Mus. Para. Emílio Goeldi. Cienc. Nat., Belém, describes several new specimens of Atretochoana eiselti from Brazil, and compares them to the known pickled ones. This turns out to be the largest tetrapod that does not have lungs: one female specimen was a meter long and weighed 570 grams (a pound is 454 grams). Here’s a photo:
Lunglessness is known in several species of salamanders and one species of frogs; breathing occurs by diffusion of oxygen through the skin.
And the head, showing the nostrils, mouth, and numerous little teeth:
The other finding of note is that, despite previous speculations that this species was limited to cold, fast-flowing streams (perhaps because such waters are highly oxygenated, helping an animal without lungs to breathe), this species was found along riverine beaches and in lakes and pools in tropical forest, including muddy mangrove pools. Apparently it gets enough oxygen to survive in those habitats; the mystery is how an animal as large as this gets sufficient oxygen solely through its skin.
Here are two more caecilians from National Geographic:
As for their evolutionary origins, here’s a candidate for something close to the common ancestor of caecelians: Eocaecelia micropoda, which has tiny limbs, clearly on the way out. It was described in the journal Nature in 1993:
This reminds me of an ancestral snake: snakes evolved from lizards by gradual diminution of the limbs, and this looks very much like an ancestral snake.
h/t: Grania Spingies
Hoogmoed, M. S., A. O. Maciel, and J. T. Coragem. Discovery of the largest lungless tetrapod, Atretochoana eiselti (Taylor, 1968) (Amphibia: Gymnophiona: Typhlonectidae),in its natural habitat in Brazilian Amazonia. Bol. Mus. Para. Emílio Goeldi. Cienc. Nat., Belém, 6: 241-262