Neotenic Arizona tiger salamander with both external gills and legs, at the onset of metamorphosis. Ambystoma tigrinum nebulosum. Photographed in captivity. From a desert pond in Hidalgo County, New Mexico, USA. Photographed under controlled conditions Photo on Sept. 16. Metamorphosis photo series over a 3-month period (UNM-0220 - UNM-0290): one 4-legged, gilled aquatic larva through metamorphosis to terrestrial adult.