When a crew of engineers stumbled across this critter while building a dam in the Amazon, many dubbed it the "penis snake," and it's easy to see why. But this phallic squirmer isn't a snake at all but an extremely rare, limbless amphibian.
Photo by Matt Roper from Mongabay. See another photo of the animal there.
Last year, a group of engineers draining a portion of the Madeira River in Brazil discovered six of these creatures, which biologist Julian Tupan identified as Atretochoana eiselti. A. eiselti is a caecilian, one of the oder of amphibians that resembles worms and snakes due to its lack of limbs. It's also the largest known tetrapod to possess no lungs; it's believed that it breathes through its skin, but it's still unclear just how the amphibian manages to intake sufficient oxygen to survive.
What's especially interesting about A. eiselti (aside from its resemblance to human genitalia) is that, until last year, the species was known only from two preserved specimens. In fact, before A. eiselti was discovered in the warm, turbid waters of the Madeira River, it was theorized that they lived instead in the cold, oxygen-rich waters of an elevated region. So this discovery has offered biologists a unique opportunity to study the species. However, given that the species is likely rare, it's a bit distressing that the species was discovered during the drainage of its habitat. In discussing the conservation of the Amazon, won't somebody please think of the penis snakes?
You can read more about A. eiselti and see more photos of the amphibians in the paper, "Discovery of the largest lungless tetrapod, Atretochoana eiselti (Taylor, 1968) (Amphibia: Gymnophiona: Typhlonectidae), in its natural habitat in Brazilian Amazonia," via Wikipedia.