Three Types of Amphibians

Three Types of Amphibians
By Priya Johnson

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Class Amphibia is classified into three orders which are Anura, Caudata and Gymnophiona. Aunra comprises frogs and toads, Caudata comprises salamanders, newts, mudpuppies, waterdogs, sirens, and amphiuma and Gymnophiona comprises caecilians. These three types of amphibians, though under one class have several distinguishing features....

Amphibians are tetrapods (four legged vertebrates) that can live on land and water alternatively. They start their lives underwater and then move on to live on land in their adult stages. This dual ability to live in water as well as on land has given them the name 'Amphibians', which has been derived from the Greek word amphibios meaning 'double life'. They belong to the class Amphibia, subphylum Vertebrata and phylum Chordata. Amphibians are cold blooded, which means that they have no control over their body temperature and are seen to take on the temperature of their surroundings. Today around 6000 species of amphibians exist of which one third are listed as endangered amphibians.

Three Types of Amphibians

Class Amphibia comprises three orders: Anura (Salientia), Caudata (Urodela), and Gymnophiona (Apoda), which is why amphibians are of three types. Frogs and toads come under the order Anura; salamanders, newts, waterdogs, mudpuppies, sirens, and amphiuma come under the order Caudata; and the third type consists of the Caecilians under the order Gymnophiona.

Order Anura (Salientia): Frogs and Toads
The term 'anura' means absence of tail, which implies that this class features the lack of the tail feature: Toads and adult frogs lack tails. Approximately 4500 species come under this category, making Anura the largest order of the three. They are found across the globe and range from few millimeters to a feet or two in length. Species of this order differ from the other two orders, Caudata and Gymnophiona, in the fact that they are four legged, wherein the hind limbs are longer thereby enabling them to climb and leap. Another area where they also differ from the other species is the fact that they are external fertilizers (union of male and female sex cells outside the body of the female). These species are also vocal and are seen to make various sounds ranging from squeaks to barks.

Frogs and toads come under this category. Though they are similar in many ways, they have different characteristics as well. Frogs are characterized by smooth, moist skin through which they absorb water. They possess lungs, though they make use of their skin to breathe as well. Their two bulging eyes are retractable in nature, which means that the frog can make its eyes go in and out of the socket. Frogs have long, webbed hind limbs which assist them while swimming, leaping and climbing, and are seen to spend a lot of time in the water. On the other hand, toads are special types of frogs which possess extraordinarily granulous, warty, dry skin, thereby enabling them to live on drier regions. Unlike the frog's long hind limbs, the toad's hind limbs are shorter and are suited for walking on land. Toads are tailless amphibians, whereas frogs possess tails in the amphibian stage though lose it in their adult life.

Order Caudata (Urodela): Salamanders, Newts, Waterdogs, Mudpuppies, Sirens, and Amphiuma
Today, there about 500 species of amphibians have been classified under this category and the number keeps getting revised according to new discoveries. The term 'Caudata' has been derived from the Latin word Cauda meaning tail. This implies that the species under this amphibian category are tailed species. This characteristic differentiates these amphibian species from those under the order Anura. Their tails are approximately equal to the length of the body, and in some species such as Oedipina, the tails are extraordinarily long. The well-developed tails enable the aquatic caudates to swim well. Caudates are also characterized by their four equal-sized limbs which they use for walking. An exception is the siren which lacks hind limbs and has reduced fore limbs instead. Unlike the anurans, this species does not leap and jump from one place to another. Sometimes, they just may run.

Caudates, unlike the anurans are not able to vocalize, except Dicamptodon ensatus which makes squeaking noises when provoked. They also vary in size and even include a species that is approximately 6 feet long called Andrias davidanius, which happens to be the world's largest amphibian. Salamanders, newts, waterdogs, mudpuppies, sirens, and amphiuma fall under this order. The lungless salamander group is the largest, comprising of over half the known caudate species. Newts and salamanders are quite similar, except for the fact that salamanders are completely aquatic and completely terrestrial, thus they can live on land or in water. However, newts live on land during summer, and throughout the winter and in spring enter the water in order to breed. The lungless salamanders are found mostly in the US, with a fraction also found in Europe. Giant salamanders (Cryptobranchidae) and Amphiuma (Amphiumidae) are among the smallest groups in the caudate order and feature only three living species under them.

Order Gymnophiona (Apoda): Caecilians
Approximately 50 known species of Caecilians come under the order Gymnophiona, and the amphibians coming under this order are the ones that have been least studied. They are characterized by long, worm-like segmented bodies and are mostly found in parts of South America, Africa and Southern Asia. These amphibians have reduced tails and also lack any kind of appendages (family Ichthyophiidae is an exception). Rather than resembling typical amphibians, they resemble eels or earthworms. They live underground and in aquatic habitats, and possess highly ossified skulls and powerful heads, which enable them to burrow deep into the soil. This is why they are seldom seen. They also have reduced eyes (nearly functionless eyes) and tiny scales, which makes them the only amphibian species to possess dermal scales.

We seldom give a second thought to amphibians and their characteristics. However, the more we hear and learn about them, the more interesting they seem. Amphibians are intriguing creatures with myriads of wonderful features. However, the tragedy is that there is a possibility of these creatures becoming extinct even before we can learn everything about them. Urbanization, environmental pollution and several other factors are pushing amphibians towards extinction. We cannot stand and watch these 'double life' unique animals just disappear into thin air!