Salamander (orig. from Persian: sam, "fire", and andarun, "within") is the common name for a group of approximately 500 species of amphibians typically characterized by slender bodies, short legs, and long tails. Their moist skin usually makes them reliant on habitats in or near water or under some protection on moist ground, often in a swamp. Some salamander species are aquatic throughout life, some take to the water intermittently, and some are entirely terrestrial as adults. They lay shelless eggs in water. They are capable of regenerating lost limbs in a process known as ecdysis. Respiration differs among the different species of salamanders. In those that retain lungs respiration is done through the gills as water passes over the gill slits. Some salamanders that are terrestrial have lungs that are used in respiration similar to that in mammals. However, some terrestrial species lack both lungs and gills and perform gas exchange through their skin, a process known as valarian respiration in which the capillary beds are spread throughout the epidermis. Hunting is yet another unique aspect of salamanders. Muscles surrounding the hyoid bone contract to create pressure and actually "shoot" the hyoid bone out of the mouth along with the tongue. The tip of the tongue is composed mucous which creates a sticky end to which the prey is captured. Muscles in the pelvic region are used in order to reel the tongue and the hyoid back to its original position. Salamanders split off from the other amphibians during the Mesozoic, and initially were similar to modern members of the Cryptobranchoidea. Any resemblance to lizards is the result of convergence of the basic tetrapod body plan, as they are no more closely related to lizards than they are to mammals. Their nearest relatives are the caecilians, little known legless amphibians.