structural:expansion
Respiration

Respiration differs among the different species of salamanders, and can involve gills, lungs, skin, and the membranes of mouth and throat. Larval salamanders breathe primarily by means of gills, which are usually external and feathery in appearance. Water is drawn in through the mouth and flows out through the gill slits. Some neotenic species such as the mudpuppy (Necturus maculosus) retain their gills throughout their lives, but most species lose them at metamorphosis. The embryos of some terrestrial lungless salamanders, such as Ensatina, that undergo direct development, have large gills that lie close to the egg's surface.

When present in adult salamanders, lungs vary greatly among different species in size and structure. In aquatic, cold-water species like the torrent salamanders (Rhyacotriton), the lungs are very small with smooth walls, while species living in warm water with little dissolved oxygen, such as the lesser siren (Siren intermedia), have large lungs with convoluted surfaces. In the lungless salamanders (family Plethodontidae and the clawed salamanders in the family of Asiatic salamanders), no lungs or gills are present, and gas exchange mostly takes place through the skin, known as cutaneous respiration, supplemented by the tissues lining the mouth. To facilitate this, these salamanders have a dense network of blood vessels just under the skin and in the mouth.

In the amphiumas, metamorphosis is incomplete, and they retain one pair of gill slits as adults, with fully functioning internal lungs. Some species that lack lungs respire through gills. In most cases, these are external gills, visible as tufts on either side of the head. Some terrestrial salamanders have lungs used in respiration, although these are simple and sac-like, unlike the more complex organs found in mammals. Many species, such as the olm, have both lungs and gills as adults.

In the Necturus, external gills begin to form as a means of combating hypoxia in the egg as egg yolk is converted into metabolically active tissue. However, molecular changes in the mudpuppy during post-embryonic development primarily due to the thyroid gland prevent the internalization of the external gills as seen in most salamanders that undergo metamorphosis. The external gills seen in salamanders differs greatly from that of amphibians with internalized gills. Unlike amphibians with internalized gills which typically rely on the changing of pressures within the buccal and pharyngeal cavities to ensure diffusion of oxygen onto the gill curtain, neotenic salamanders such as Necturus use specified musculature, such as the levatores arcuum, to move external gills to keep the respiratory surfaces constantly in contact with new oxygenated water.