Class Amphibian (Theory)

     

               

Class Amphibian: General Characters and Classification |

These are the first cold blooded vertebrates from evolution point of view. There are about 3000 species of class Amphibian. They are almost found in freshwater or moist land. Amphibians are not found in marine water except few species.   

General Characteristics of Class Amphibians:

 

1.      Amphibians are cold blooded animals. i.e. ectothermic.

2.      They can live in water on land hence they are called amphibians.

3.      Body is divisible into head trunk. In some amphibian neck is absent.

4.      Tail is present in few member.

5.      Respiration by lung, gills, skin and bucco-pharyngeal cavity. 

6.      Scales are absent.

7.      The skin is smooth and moist.

8.      Mucous glands are present in skin.

9.      Two pairs of limbs are present except caecilions (Ichthyophis- limbless amphibian).

10.  Gills are present in the larval stage. In some adults in addition to lung externals gills are present.

11.  Kidney is meso-nephric.

12.  Urinary bladder is present in frog.

13.  In frog and toad are ureotelic (Urine is excreted)  Salamander are aminotelic (Amonia is excretory product) .

14.  Heart is three chambered.

15.  Presence of cloaca (Alimentary canal, urinary and reproductive track open in common chamber).

16.  Nictitating membrane is well developed.

17.  Middle ear and inner ear is present.

18.   Ten pair of cranial nerve.

19.  Generally they are oviparous. Salamander is viviparous.

20.  Fertilization is external (Grog and Toad).

21.  Metamorphosis is occurs.

22.  Larval stage is called tadpole. 

Classifications of Living Amphibians: Living Amphibians are divided into three orders:  

Order 1. Apoda (Gymnophiona or Caecilia/ Limbless Amphibians):

1.      They are limbless amphibian.

2.      Scales are present hidden in to the skin. 
3. Male vocalize to attract female.  

4.      They are viviparous amphibian.some forms are oviparous.
5. Fertilization is external.

6.      Extensive parental care by coiling body around eggs till hatching. 

7.      They are called “blind worms” or caecilians.
8. Eyes are covered with skin. 
9. Adult are insectivorous or carnivorous.

Order- Urodela or Caudata : Eg.  Salamanders

1.     Near about 620 species,  are included into the order  urodela.

2.     Some are aquatic, other terrestrial, and some that live on land only as adults.

3.     They are tailed amphibians.

4.     They are tetrapod having two pairs of limb i.e. fore limb and hind limb.

5.     There are presence of external gills and gill slits in aquatic larva when present.

6.     Many salamanders have a biphasic life cycle. Larval forms are aquatic with external gills and a metamorphosed terrestrial adult form breathes by lungs and/or through moist skin.

7.     In some salamander species lack metamorphosis and some larval characters remain in larval condition throughout their life.

8.     In adult externals gills are present along with lung. Majority of the salamander are lung-less and breath through gills (Plethontid), some form gills are absent and they use lung for breath (Amphiumas).

9.     Tympanum is absent.

10.         Presence of true teeth on both the jaws.

11.         Salamanders are carnivorous prey on small arthropods.

12.         Fertilization is internal.

Order – Anura (Tailless Amphibians) eg. Frog, Toad, Tree frog etc.

1.     Order Anura includes divers group of vertebrates. Near about 595 species found all over the world except Antarctica.

2.     These are the vertebrates able to live in water and on land hence called amphibians. (Two habitats).

3.     Neck is absent.

4.     Skin is moist and slippery.

5.     Tongue is long and sticky.

6.     Tail is present in larval condition.

7.     Larva of Anura are called tadpole respire through gills.

8.     Adult respire with skin, bucco-pharynx and lung.

9.     Tadpoles are herbivorous while adults are insectivorous.

10.         Fore limb and hind limbs are present. Hind limbs are used for jumping and swimming.

11.         Toes are webbed, used for swimming into water.

12.         In male vocal sacs are present.

13.         Caudal vertebrae are fused formed rod like urostyle bone.

14.         Parental care is extensive in some frogs by constructing nests.

15.         They are insectivorous.

16.         Fertilizations is external.

17.         They are oviparous.

18.          Cloaca is present. 


Parental care in Amphibian
 

Mammals

 Mammals

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 1.    Mammals are warm-blooded animals.
2.     The body is divisible into the head, neck, thorax, and abdomen
2.    They give direct birth to young ones. Few mammals lay eggs (Platypus) Some mammals
       (Kangaroo) give birth to immature young ones.
3.    They found in a variety of habitats- forests, mountains, water, polar ice caps, deserts, etc.
4.    Presence of mammary glands.
5.    Presence of fur on the body.
6.    Presence of pinnae.
7.    Presence of forelimb and hind limbs used for running, climbing, walking swimming, flying etc.
8.    Presence of different kinds of teeth
9.    Heart is four-chambered.
10.    Respiration by lung.
11.    They are homoeothermic animals (warm Blooded) maintains constant body temperature.
12.    Sexes are separate.
13.    Fertilization is internal.
14.    They give direct birth to young ones with few exceptions.
15.    Development is direct.

Examples: Oviparous – Platypus; Viviparous – Kangaroo, Flying fox), Delphinus (Common dolphin), Balaenoptera (Blue whale), etc.

1.              Class Mammalia is classified into three sub-classes , which are :

Sub-class: Prototheria

2.              They do not give birth but they lay eggs and incubate them, The mother suckles its young with milk secreted from its mammary glands on its abdomen, They have a cloacal opening through which urine, feces, and eggs emerge, Such as Duck-billed platypus and Spiny ant-eater.

Sub-class: Metatheria

3.              They give birth immature youngs, The mother suckles its youngs from nipples found inside a special pouch at the bottom of its abdomen where it keeps its young until they become fully grown, Such as Kangaroo.

Sub-class: Eutheria

4.              They are placental mammals that give birth fully developed youngs, Their mother suckles its young with milk secreted from its mammary glands.

5.              Eutheria includes many animals that are headed by human and it is divided into many orders , the most important ones are Edentata , Insectivora , Carnivora , Perissodactyla , Artiodactyla , Cetacea , Rodentia , Lagomorpha , Chiroptera , Proboscida and Primates .