Amphibia: General Characters and Classification
GENERAL CHARACTERS:
1. Cold blooded vertebrates.
2. Skin smooth or rough, rich in glands which kept it moist.
3. Scales, if present, are hidden in the skin.
4. Skull articulates with the atlas by two occipital condyles.
5. Auditory columellar apparatus fitting into fenestra ovails.
6. Vertebrae are acentrous, pseudocentrous and notocentrous.
7. Limbs tetrapodus pentadactyle type.
8. Red blood corpuscles (R.B.C.) are biconvex, oval and nucleated.
9. Heart is divided into two atria and one ventricle and it has a conus provided with valves.
10. Aortic arches are symmetrical. 11. Gills are present at least, during some early stages of development.
12. Kidneys are provided with persistent nephrostome.
13. Lateral sense organs are present during some stages of development.
14. Vagus is the last cranial nerve.
15. Eggs with gelatinous covering, usually laid in water.
16. The larvae pass through an aquatic stage before metamor-phosing into adult.
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CLASSIFICATION:
Different authors have classified Class Amphibia with their own conception.
Parker and Haswell divided the class into eight orders, five extinct and three living.
It has been customary to place the extinct orders together in a subclass Stegocephalia (Sedg- wick).
Dr. Gadow classified extinct orders into a subclass Lisiamphibia. G. Kingsley Noble (1931) classified class Amphi. bia into six orders.
The classification followed under these lines is of G. Kingsley Noble (1931).
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Extinct Amphibia:
Order: 1. Labyrinthodontia.
1. These were crocodile or salamander-like Amphibia.
2. They lived from the Lower Carboniferous to the Triassic period.
3. They had a skull completely roofed over with bones.
4. Many more bony elements were present in their skulls than occur today in the modern Amphibia.
5. Enlarged teeth with greatly folded dentine found in both the jaws.
6. Many species were aquatic but others may have been terrestrial.
Example: Eryops.
Order: 2. Phyllospondyli
1. They were small, salamander-like Amphibia.
2. Found in the Carboniferous and Permian deposits.
3. Vertebrae tubular with spinal cord and notochord lying in one cavity.
4. Well marked transverse processes with stout ribs.
5. Pubis cartilaginous.
6. Four fingers and five toes.
7. A clavicle, cleithrum and scapula were present but the coracoid remained cartilaginous.
8. The skull roof had a separate quadrato-jugal and a lacrimal.
Order: 3. Lepospondyli
1. Small Carboniferous and Permian Amphibia.
2. Vertebrae composed of a single piece, the neural arch being continuous with the centrum.
3. Ribs articulate with the column intervertebrally.
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Living Amphibia:
Order: 4. Gymnophiona or Apoda
1. Primitive burrowing forms.
2. Body is elongated eel-type.
3. Limbs and tail are absent. 4. The skin is provided with numerous transverse grooves or wrinkles.
5. Minute scales are found embedded in the grooves of the skin in some forms.
6. Copulatory organs are present in males.
Examples: Ichthyophis, Uraeotyphlus, Siphonops.
Order: 5. Caudata or Urodela
1. Body with distinct head, trunk and tail.
2. Limbs are of equal size.
3. Skin devoid of scales.
4. Teeth are present in both the jaws.
5. Usually oviparous.
6. Larvae are aquatic like adults or resemble adults in form.
Suborder: 1. Cryptobranchoidea
1. Body is depressed.
2. Skin is soft and flabby.
3. Eye-lids are absent.
4. Gills are absent in adults.
5. Fertilization is external.
Examples: Cryptobranchus, Hynobius.
Suborder: 2. Ambystomoidea
1. Teeth present in transverse rows across the posterior margins of vomer.
2. Eyelids are present.
3. Fertilization is internal.
4. Exhibits the phenomena of neoteny or paedogenesis, i.e., larva becomes sexually mature and reproduces.
Examples: Ambystoma, Axolotl larva,
Suborder: 3. Salamandroidea
1. Eyelids are present or absent.
2. Usually either gills or lungs are present but in some forms respiration by skin.
3. Fertilization is internal.
4. Vertebrae are amphicoelous.
5. Usually viviparous.
Examples: Salamandra, Amphiuma, Triton.
Suborder: 4. Proteida
1. Body is depressed.
2. Permanent larval forms,
3. 3. Tail provided with fin.
4. External gills are always present.
5. Eyelids are absent.
6. Permanently aquatic.
Examples: Proteus, Necturus.
Suborder: 5. Meantes
1. Body is slender eel-type.
2. Permanent larval forms.
3. Hind limbs are absent.
4. External gills are well developed.
5. Eyelids are absent.
6. Jaws with horny covering.
7. Fertilization is external.
8. Completely aquatic.
Example: Siren
Order: 6. Anura or Salientia
1. Body is short and broad.
2. Head and trunk are fused.
3. Neck and tail are absent.
4. Fore limbs are short while hind limbs are long.
5. Gills are absent. Respiration is by lungs.
6. Fertilization is usually external.
Suborder: 1. Amphicoela
1. Vertebrae are amphicoelous.
2. Two tail waging or relict muscles.
3. Fertilization is internal.
Examples: Ascaphus, Liopelma,
Suborder: 2. Opisthocoela
1. Vertebrae are opisthocoelous.
2. Free ribs either in larva or adult.
Examples: Alytes, Pipa, Bombinator.
Suborder: 3. Anomocoela
1. Vertebrae are procoelous.
2. Sacral vertebrae are fused with urostyle 3. No free ribs.
4. Skin is rough.
Example: Pelobates.
Suborder: 4. Procoela
1. Vertebrae are procoelous.
2. Urostyle articulates ooodyles. with the last vertebra by two
Examples: Bufo, Hyla.
Suborder: 5. Diplasiocoela
1. First seven vertebrae are procoelus.
2. Eighth vertebra is amphicoelous.
3. Sacral vertebra acoelous and bears two condyles posteriorly for the attachment with the urostyle.
4. Pectoral girdle is fused with sternum.
5. Ribs are absent.
Examples: Rana, Rhacophorus.
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