Question

In the amphibian order Urodela,
(a)Limbs are small in front and long behind.
(b)Limbs are absent in adults.
(c)Hind limbs are absent in adults.
(d)All of the above.

Answer 1

Hint: An example of the amphibian Urodela is salamander which has a lizard-like appearance. Adult salamanders have a tetrapod body and a long tail. They have specialized features for the purpose of crawling.

Complete answer:
Urodela is an order of amphibians with a well-developed tail and is often long. It includes salamanders, tritons, and species allied to it. They are often colored brightly and range in length from a few centimeters to around 1.5 meters. Limbs can vary from short in front and long in behind.
Amphibians can be classified into three classes:
-Urodela ("tailed-ones"), example: Salamanders
-Anura ("tailless ones"), for example: Frogs
-Apoda ("legless ones"), for example: Caecilians
Salamanders are a group of amphibians usually lizard-like in appearance, with slender bodies, blunt snouts, short limbs attached to the body at right angles, and the presence of a tail in both larvae and adults. All the families of salamanders are classified under the order Urodela.
Salamanders rarely have more than four toes on their front legs and five on their rear legs, although some species have fewer digits and some species lack hind limbs. Usually, their permeable skin makes them dependent on environments in or near water, or other cold, humid areas. Throughout their lives, some salamander species are completely aquatic, others take to water intermittently and some as adults are entirely terrestrial. They are able to regenerate the lost limbs, as well as other damaged parts of their bodies.

So, the correct answer is ‘Limbs are small in front and long behind’.

Note: Salamanders can regenerate whole limbs and parts of major organs, a capacity that relies on their immune systems. An analysis of axolotl (Ambystoma mexicanum), an aquatic salamander, shows that in the early stages of regenerating the damaged limbs, immune cells called macrophages are essential. The regeneration of limbs is made possible in these organisms because of the activation of undifferentiated cells called stem cells. Humans have these stem cells but they are not activated and hence we cannot regenerate limbs.