They seem very dirty, sluggish to us that majority of us do not like them but they are a part of our ecosystem and are helpful in making the ecological balance. They are salamanders. They belong to class Amphibia which means that they are able to live in water as well as land. About 5,000 species of salamander are known at present. They bear slender bodies, stout noses and long tails. All the fossil species are categorized under order Caudata while the living species are placed under order Urodela. Fore-legs have four toes while hind legs have 5 toes. Skin is perfectly adapted for living both in water as well as on land. Some are fully aquatic and some completely terrestrial while some live partly in water and partly on land. Power or regeneration is highly developed.
Mature salamanders share their body appearance with that of lizards while some show eel-like bodied with reduced limbs. Claws are totally absent. They are also brightly colored throughout the year while in some only males becoming brightly colored during the breeding season. Some prefer to live underground and lack skin pigment and may be either white or pink in body coloring. Some are relatively very short like the minute salamanders measuring only 2.7 cm in length while some attain good body lengths like the Chinese giant salamanders measuring 1.8 m and weighing up to 65 kg. Majority of species attain a length between 10-20 cm. they are known to shed their skin in order to grow and consume the shed skin. Mode of respiration is also variable among different species. Some respire through gills in absence of lungs. The gills are visible as hairy tufts on either side of the head while the amphiumas have both internal gills as well as gill slits. Terrestrial species respire through lungs but the structure of lungs is very simple in comparison with that of mammals. Olms have both gills as well as lungs. Some species lack both gills and lungs and respiration through skin known as valerian respiration in which many capillary beds are scatter through the epidermis around mouth. Some with lungs also respire in this manner.
Skin secretes large amount of mucus which keeps them moist when they move on dry land. Mucus helps in maintaining salt water balance as well acts as a lubricant during swimming. Skin glands also secret poison and pheromones during courtship. The tip of tongue is also kept moist with mucus which helps in prey capture. Some highly aquatic species lack muscle in the tongue so it can not be used in prey capture. Most species bear teeth in both upper and lower jaws. They use trichromatic color vision of ultraviolet range for prey capture. Subterranean salamanders have reduced eyes covered with a flap of skin. Some highly aquatic species have lateral line system like that of fishes for detecting pressure changes. External ear absent and middle is vestigial. Tail is shed off on being attacked by predators which later on regenerates by the process of autotomy. Limbs if damaged may also be regenerated.
They are found in all continents except Antarctica, Australia and most parts of Africa. One third species have been recorded from North America. The Appalachian Mountains house highest population of salamanders in the world. Salamanders prefer to live in arid and dry habitats of the northern hemisphere. They are found in creeks, ponds, brooks and other moist locations. Life history resembles that of frogs and toads. In majority of species fertilization is internal where the male deposits the sperm contained in sac-like structures inside the cloaca of female. Female is oviparous and lays eggs either near the ponds or on moist soil. Ovoviviparous species are also known. Eggs hatch into larvae which are either fully aquatic or fully terrestrial and bear gills. Larvae may be with or without legs. Larval period may range from few days to many years. Some lack larval stages. Neoteny has been observed in many salamander species where the larva retains gills even after attaining sexual maturity. Axolotl larva of the tiger salamander is a common example of neoteny.
Salamanders have been attacked by a fungal disease known as chytridiomycosis which is responsible for their population reduction. Loss of habits due to deforestation is also one of the major causes for population reduction. There are 10 families under the order Caudata. Many myths and legends are famous for them. They are generally considered as symbols of fire. People believe that they live under the logs and when logs are kept in fire they try to come out. People believe that they have originated from flames. They deserve special place in the writings of Leonardo da Vinci.
The power of limb generation in salamanders is a burning issue in the field of research and scientists are working in this area tirelessly. Axolotl larva is next in this context for neoteny.