Urodela

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Salamanders, Newts and relatives

Fire Salamander, Salamandra salamandra

Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Class:	Amphibia
Order:	Caudata/Urodela

Urodela is the amphibian order comprising salamanders and newts.

1 Distribution
2 Meaning
3 Biology
4 Characteristics
5 Examples
6 See also
7 References

[edit] Distribution

Urodela is one of three orders composing the modern class amphibia. The order Urodela makes up 9% of global amphibian species equalling 558 species out of 6153 species of amphibians worldwide. Anurans are the most numerous amphibian order while gymnophiona is the least numerous.

Newts and salamanders are found on all continents except for most of Africa, Australia and Antarctica. One-third of the known urodeles, are found in North America. The highest concentration of these is found in the Appalachian Mountains region and doesnt exist any longer.

[edit] Meaning

The name Urodela is derived from Greek. The word can be divided into 2 parts. ' Ur ' & ' delos ' - Ur = tail; Delos = visible.
They have another name: Caudata. Cauda means tail in Latin.
The meaning of Urodela/Caudata is an animal with a body which is lizard-like and has a distinct post-anal tail

[edit] Biology

The newts appear to be rather primitive amphibians because they have a rather simple shape.^[1]

Note that their legs are rather weak and small, and that the body often partly drags along the ground when the animal is moving. They rely on lateral undulations of the body to assist with movement. But these primitive features are probably deceptive, and there is no evidence to suggest that they arose any earlier than the other orders of modern amphibia.

[edit] Characteristics

1. Two pairs of weak and equal limbs are present.
2. Skin is without exoskeleton.
3. Teeth are Present on both jaws.
4. Tympanum is present.
5. Eyelids may be present or absent
6. Gills are retained throughout (perinnibranchiates) the life. In some they are lost in the adults (caducibranchiates).
7. Well developed Lateral Line sense organs are present.
8. They show a transition of aquatic life to terrestrial mode of life.
9. Necturus like animals are completely aquatic, but some animals like Amphiuma are traditional forms losing gills but retaining gills slits, while Ambystoma is a complete lung breathing form of adult condition.

[edit] Examples

Necturus (mud puppy): It is with external gills and lateral line sense organs. Lungs are greatly reduced. It is found in eastern parts of USA.
Amphiuma (Congo eel): External gills are absent. Limbs are rudimentary. RBCs are largest among that of the vertebrates. It if found in the southern parts of N. America.

Necturus

Amphiuma

Tylotriton

Ambystoma: It is a terrestrial newt. Larva is Axolotl. Axolotl larva becomes sexually mature with out metamorphosis due to lack of iodine in the extremely cold water, in which it lives. Iodine is required for the secretion of thyroxine, which stimulates the metamorphosis in amphibians. Deficiency of the thyroxine results in extended larval condiitions and precocious sexual maturity, which is called neoteny. It leads to paedogenesis.
Andrias: These are the giant salamanders of China and Japan and are the largest caudate known.
Tylototriton: It occurs in the eastern Himalayas region and is the only Indian caudate species.