The skin lacks scales and is moist and smooth to the touch, except in
newts of the Salamandridae, which may have velvety or warty skin, wet to the touch. The skin may be drab or brightly colored, exhibiting various patterns of stripes, bars, spots, blotches, or dots. Male newts become dramatically colored during the breeding season. Cave species dwelling in darkness lack pigmentation and have a translucent pink or pearlescent appearance. Salamanders range in size from the
minute salamanders, with a total length of , including the tail, to the
Chinese giant salamander which reaches and weighs up to . All the largest species are found in the four families
giant salamanders,
sirens,
Congo eels and
Proteidae, which are all aquatic and obligate
paedomorphs. Some of the largest terrestrial salamanders, which go through full metamorphosis, belong to the family of
Pacific giant salamanders, and are much smaller. Most salamanders are between in length.
Trunk, limbs and tail An adult salamander generally resembles a small lizard, having a basal
tetrapod body form with a cylindrical trunk, four limbs, and a long tail. Except in the family Salamandridae, the head, body, and tail have a number of vertical depressions in the surface which run from the mid-dorsal region to the ventral area and are known as
costal grooves. Their function seems to be to help keep the skin moist by channeling water over the surface of the body. have an eel-like appearance. Some aquatic species, such as
sirens and
amphiumas, have reduced or absent hind limbs, giving them an
eel-like appearance, but in most species, the front and rear limbs are about the same length and project sideward, barely raising the trunk off the ground. The feet are broad with short digits, usually four on the front feet and five on the rear. Salamanders do not have claws, and the shape of the foot varies according to the animal's habitat. Climbing species have elongated, square-tipped toes, while rock-dwellers have larger feet with short, blunt toes. The
tree-climbing salamander (
Bolitoglossa sp.) has plate-like webbed feet which adhere to smooth surfaces by suction, while the rock-climbing
Hydromantes species from California have feet with fleshy webs and short digits and use their tails as an extra limb. When ascending, the tail props up the rear of the body, while one hind foot moves forward and then swings to the other side to provide support as the other hind foot advances. In larvae and aquatic salamanders, the tail is laterally flattened, has dorsal and ventral fins, and undulates from side to side to propel the animal through the water. In the families
Ambystomatidae and Salamandridae, the male's tail, which is larger than that of the female, is used during the
amplexus embrace to propel the mating couple to a secluded location. In terrestrial species, the tail moves to counterbalance the animal as it runs, while in the
arboreal salamander and other tree-climbing species, it is
prehensile. The tail is also used by certain
plethodontid salamanders that can jump, to help launch themselves into the air. The animal often then eats the resulting sloughed skin. Mature adults of some salamander species have "nuptial" glandular tissue in their
cloacae, at the base of their tails, on their heads or under their chins. Some females release
chemical substances, possibly from the ventral cloacal gland, to attract males, but males do not seem to use pheromones for this purpose. In some
plethodonts, males have conspicuous mental glands on the chin which are pressed against the females' nostrils during the courtship ritual. They may function to speed up the mating process, reducing the risk of its being disrupted by a predator or rival male. The gland at the base of the tail in
Plethodon cinereus is used to mark
fecal pellets to proclaim territorial ownership.
Vision The eyes of most salamanders are adapted primarily for vision at night. In some permanently aquatic species, they are reduced in size and have a simplified
retinal structure, and in cave dwellers such as the
Georgia blind salamander, they are absent or covered with a layer of skin. In amphibious species, the eyes are a compromise and are
nearsighted in air and
farsighted in water. Fully terrestrial species such as the
fire salamander have a flatter lens which can focus over a much wider range of distances. To find their prey, salamanders use
trichromatic color vision extending into the
ultraviolet range, based on three
photoreceptor types that are maximally sensitive around 450, 500, and 570 nm. The larvae, and the adults of some highly aquatic species, also have a
lateral line organ, similar to that of fish, which can detect changes in water pressure. The opercularis system consists of two ossicles: the columella (equivalent to the
stapes of
higher vertebrates) which is fused to the skull, and the operculum. An opercularis muscle connects the latter to the pectoral girdle, and is kept under tension when the animal is alert. The system seems able to detect low-frequency vibrations (500–600 Hz), which may be picked up from the ground by the fore limbs and transmitted to the inner ear. These may serve to warn the animal of an approaching predator.
Vocalization Salamanders are usually considered to have no voice and do not use sound for communication in the way that frogs do. Before mating, they communicate by pheromone signaling; some species make quiet ticking, clicking, squeaks or popping noises, The
California giant salamander can produce a bark or rattle, and a few species can squeak by contracting muscles in the throat. The arboreal salamander can squeak using a different mechanism; it retracts its eyes into its head, forcing air out of its mouth. The
ensatina salamander occasionally makes a hissing sound, while the
sirens sometimes produce quiet clicks, and can resort to faint shrieks if attacked. Similar clicking behaviour was observed in two European newts
Lissotriton vulgaris and
Ichthyosaura alpestris in their aquatic phase. Vocalization in salamanders has been little studied and the purpose of these sounds is presumed to be the startling of predators.
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. 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. ==Feeding and diet==