General characters amphibia

amphibian general characters

1. Amphibia- General characters B.Ashok kumar Lecturer in Zoology KRK Govt Degree College Addanki-523201 @9652929696,9441635264 [email protected]

2. Introduction Amphibians are cold blooded vertebrates. In the Devonian period of palaeozoic era they were originated from fishes, In the carboniferous period, they increased their number, hence that period is called ‘ Age of amphibians’

3. According to Romer Dipnoi fishes are the “ uncles of Amphibians ” According to Newman “ Dipnoi and amphibians had same grand father .”

4. General characters of Amphibians 1) Amphibians are cold blooded vertebrates which can hue on land and in water. 2) Amphibians show four limbs with which they can swim in water and jump or walk on the land, (But In apoda limbs are absent.) 3) In Amphibians  animals exoskeleton is absent. But in apoda animals small cycloid scales are present. 4) In Amphibians the adult animals lungs are present. Gills are absent. But In some urodelans the gills are present.

5. 5)Amphibians Skin is a respiratory organ. 6) The Amphibians skull is dicondylic . 7) Amphibians Ribs are absent. 8)In Amphibians The body divisible into head and trunk Tail is present in, urodela animals. 9)Amphibians  Digestive system is well developed. A well developed liver Is present

6. 10) External ear is absent. Middle and inner ears are present, the middle ear columella auris Is present. 11)Amphibians Heart is 3 chambered with 2 auricles and 1 ventricle The blood contains R.B.C. They are nucleated. They contain hemoglobin. 12) Blood vascular system contain hepatic and renal portal systems. 13) Amphibians Kidneys are mesonephric . Urinary bladder is present. It stores urine.

7. 14) Central nervous system is well developed. The brain occupies completely the cranial cavity. The brain is divided into fore, mid and hind brains. Brain continuous as spinal cord. 15)10 pairs of cranial nerves will arise. 16) Sexes are separate. 17) Male and female can be indentified - Sexual dimorphism. 18) In Amphibians the life history a larva stage may be present. 19) Amphibian Eggs are telolecithal , Cleavage is holoblastic unequal.

8. Classification of Amphibia J.Z.Young classified Amphibia into three sub classes Labarynthodontia Lepospondyli Lissamphibia

9. Sub-class: Labyrinthodontia Folded teeth Extinct Enamel and dentine at the base of tooth was folded Some had scales Others had dry leathery skin Includes three orders i . ichthyostegalia eg : Ichthyostega Ii. Temnospondyli eg : Eryops Iii.Anthracosauria eg : Seymouria

10. Sub-class: L epospondyli Small salamander like extinct amphibians Eg : Diplocaulus

11. Sub- class: Lissamphibia Based on the characters of present day (extant) amphibians( Lissamphibia ) are classified Into 3 orders. Order I . Anura - (Frogs and Toads). Order 2. Urodela - (Salamanders). Order 3 Apoda - (Limbless amphibians)

12. Order 1. Anura ( Gr.An =Without, oura =tail) Salientia ( L.saliens =leaping) This order Anura includes frogs and toads. They can live in water and on land. Inhabits tropical and temperate regions Body is short and broad with head and trunk The fore limbs are small, the hind limbs are long for leaping and swimming, feet are webbed . In the adult stage tail is absent Skin is scaleless Vertebrae are procoelous and are fewer(generally 9) Caudal vertebrae fuse to form urostyle Ribs are reduced/ absent Teeth are on upper jaw or absent Gills and gill slits are absent in adults Vocal cards are present They show a pair of eyes. tympanic membranes. Their Life history includes a larval stage called tad-pole larva. Eg:1 . Alytes . (Mid wife toad).  2. Cacopus (Burrowing frog). 3. Xenopus (Clawed Toad), 4. Bufo .

13. Order 2. Urodela / Caudata ( Gr.Oura =Tail; Delos=visible;, L.Cauda =tail; ata = bearing) This order includes Salamandars and newts. These urodelans are more in North America. Hence North America is called Head Quarters of Urodeles The body is divisible into head, trunk and tail. The fore limbs and hind limbs are equal and weak. Scaleless Vertebrae opistocoelous ( amphicoelous in some)and numerous Ribs are present Teeth on both the jaws Vocal cords are absent In some adults the gills are presents Middle ear is absent, E yes are small and eyelids are present in some Copiulatory organ is absent, fertilisation is internal Some forms show neoteny and paedogenesis . In North India only one species is available. Tilototriton venvcosa . In South India urodelan animals are absent. 1.Necturus 2. Proteus(Mud puppy).(Blind salamander) 3. Molge (Newt). 4. Amblystoma

14. Order 3. Apoda / Gymnophiana These animals are limbless. Hence they me called Apoda . The body is long and snake like. Hence it Is called gymnophiona . The body is divisible into head and hunk. Tail is absent On the head two eyes are present. They covered by skin and scales. Hence they are blind ( Cecaelians ). Vertebrae are amphicoelous and numerous Lungs are asymmetrical . The skin shows minute cycloid scales. in the male apoda animals copulatory organs present. Fertilization is internal. 1. lchthyophis (Limbless amphibian). 2. Gegenophis (Limbless amphibian). 3. Ureotyphlus .