Plethodontid salamanders have no lungs at any adult stage. Gas exchange occurs across the moist skin and the buccopharyngeal lining, which works because these animals are small, thin-bodied and ectothermic, with low oxygen demand. The trade-off is a strict dependence on moisture and cool conditions.
The loss reorganised the head. In lunged salamanders, the throat and hyobranchial apparatus are used to pump air. Freed from that job, plethodontids evolved a hyobranchial skeleton specialised for tongue projection, and several lineages, particularly the tropical bolitoglossines, can fire a tongue a substantial fraction of body length to capture prey in milliseconds. That feeding mechanism is among the fastest in vertebrates.
Why lungs were lost is still contested. The long-standing explanation invoked fast mountain streams where lungs cause unwanted buoyancy, but that scenario has been challenged, and alternatives emphasising skin respiration in cool, moist conditions are now argued. The family is also the reason salamander diversity peaks in the Appalachians and in Neotropical cloud forest, not in the temperate ponds most people picture.