Caratterestiche natural amphibian 
With their slender body and long tail, some amphibians such as salamanders, can be exchanged for lizards and other reptiles. However, this is only a superficial resemblance: there are numerous anatomical differences that distinguish amphibians from reptiles, for example, the bare skin and musk of the first, as opposed to dry and scaly seconds.
The skin of amphibians has a vital role to ensure their survival in the first place that protects them from dehydration through an outer layer of keratin , second helping to breathing integrating the function of the lungs, which in general, species that have them are inefficient: it is in fact rich in blood vessels and is kept moist by special mucous glands, so that trade gases with the environment. It is also rich in glands that secrete substances irritating or poisonous used as a deterrent against predators, and contains pigmented cells that expand and contract by changing the color of the skin in order mimetic . teeth and tongue shape varies from species to species and can sometimes be off. In general, the teeth do not have chewing function, but the taking of food, the language, which in some frog species is fixed to the palate before and after, it is often everted and is used to catch small prey such as insects.
often amphibians of the two sexes differ in size and color, also the males may show more than the female vocal sacs, the first finger is swollen and wrinkled skin.
| internal anatomy and physiology: |
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Many devices ( locomotive, digestive, nervous ) anatomy of amphibians are similar to those of higher vertebrates. The skeleton is more robust than that of fish from which amphibians have evolved, and therefore more suitable to support its body out of the water. The muscles varies according to the groups: in urodeles, in which water moves with lithe movements of the body, is quite similar to that of fish, in anurans, however, is such that the long jumps which are capable of.
The breathing apparatus of vary depending on the species and the environments in which they are adapted. The most frequent is that in which the larval stage , aquatic, has gills and lungs of the adult. In some amphibians, however, the gills are retained allo stadio adulto, e in altri mancano completamente sia le branchie che i polmoni; in questi ultimi casi, gli scambi gassosi avvengono esclusivamente attraverso la cute. Il cervello degli anfibi è caratteristico, in quanto ha un cervelletto molto ridotto. Il cuore dell’adulto presenta due atri e un ventricolo; è quindi più evoluto di quello dei pesci, che è suddiviso in un solo atrio e un solo ventricolo.
Temperatura corporea:
| Come i rettili, gli anfibi sono animali a sangue freddo; quindi la loro temperatura body varies depending on the environment and is generally much lower than that of birds and mammals. Having to rely on external heat sources, in cold regions amphibians spend the winter in a state of hibernation . Reproduction and Development: |
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Most amphibians reproduce in water or high humidity. The eggs, fragile and jellies are usually laid in ponds and swamps. In most species they hatch, giving rise to aquatic larvae called tadpoles . These, with gills, to become adults undergo metamorphosis , ie major changes in the body, both external and internal. Some amphibians, however, reach sexual maturity at the larval stage and metamorphosis should never meet, and this condition, characteristic dell'urodelo Ambystoma mexicanum (Axolotl ) is called neoteny .
adult amphibians are carnivorous and feed mainly on insects , snails and worms , tadpoles, however, are mainly herbivores. During the metamorphosis from tadpole to adult, so even the digestive system undergoes a profound transformation.
Evolution:
Based on the findings from studies paleontological , amphibians evolved from a group of fish (the crossopterigi ; see Celacantiformi ) with lobed fins and tough at the beginning of the Devonian period . During the dry, probably often in this period, these creatures came crawling from the ponds drained to breathe air with lungs that were equipped with rudimentary, or look for other pools of water where they are established. With the passage of time and then developed a relative independence from the water. Amphibians knew a time of great exuberance during the Carboniferous , but many of them had already been extinguished when, in ' Mesozoic era, appeared modern amphibians. Today the class, though very diverse, which is among the vertebrates has the fewest species. Mainly threatened by destruction of their habitat by man, the populations of amphibians are still decrease.
