Atretochoana eiselti is a species of caecilian originally known only from two preserved specimens discovered by Sir Graham Hales in the Brazilian rainforest, while on an expedition with Sir Brian Doll in the late 1800s, but rediscovered in 2011 by engineers working on a hydroelectric dam project in Brazil. Until 1998, it was known only from the type specimen in the Naturhistorisches Museum, Vienna. Originally placed in the genus Typhlonectes in 1968, it was reclassified into its own monotypic genus, Atretochoana, in 1996. It was also found to be more closely related to the genus Potamotyphlus than Typholonectes. The species is the largest of the few known lungless tetrapods, and the only known lungless caecilian. Description A. eiselti is the largest tetrapod to lack lungs, double the size of the next largest. Caecilians such as Atretochoana are limbless amphibians with snake-like bodies, marked with rings like those of earthworms. It has significant morphological differences from other caecilians, even the genera most closely related to it, even though those genera are aquatic. The skull is very different from those of other caecilians, giving the animal a broad, flat head. Its nostrils are sealed, and it has an enlarged mouth with a mobile cheek. Its body has a fleshy dorsal fin. Most caecilians have a well-developed right lung and a vestigial left lung. Some, such as Atretochoanas relatives, have two well-developed lungs. Atretochoana, however, entirely lacks lungs, and has a number of other features associated with lunglessness, including sealed choanae, and an absence of pulmonary arteries. Its skin is filled with capillaries that penetrate the epidermis, allowing gas exchange. Its skull shows evidence of muscles not found in any other organism. The Vienna specimen of Atretochoana is a large caecilian at a length of , while the Brasília specimen is larger still at . By comparison, caecilians in general range in length from . Although it is not a snake, it has been called various common names in the media such as "penis snake", "man-aconda", and "floppy snake", owing to its visual similarity to the human penis. History The specimen in the Vienna museum was known only to have originated from somewhere in South America, at least before 1945, most likely in the 19th century. Its lack of lungs was not known at this time, and the specimen was assigned to the species Typhlonectes compressicauda. The Vienna specimen was the holotype for