CLASS AMPHIBIA
Class Amphibians mainly live in water or damp places; none in salt water. They are the commonest in moist temperate regions but some are tropical; one frog ranges into Arctic circle and tree frogs occur above 400 meters in Sierra Nevada of California. Some toads are tree toads and live in deserts, some are nocturnal. The hell bender (Cryptobranchus). mud puppy (Necturus) and Congo eel (Amphiuma) are strictly aquatic. Some frogs are purely arboreal. Land salamanders hide under stones and logs. Amphibians partly pass their life in water and partly on land (Gr., amphi = dual; bios = life). They are the lowest and earliest tetrapods evolving from Devonian and onwards. Class Amphibians have educational, experimental and food value.
DIAGNOSTIC CHARACTERS OF CLASS AMPHIBIA
- Amphibious life (on land and in water)
- Skin moist and glandular. No Scales. Chromatophores in skin.
- Tetrapoda, Limbs 2 pairs. Some limbless.
- Nostrils two, connected with mouth cavity.
- Endoskeleton bony.
- Heart three chambered, 2 auricles and 1 ventricle.
- Development includes tadpole larva.
CLASSIFICATION OF CLASS AMPHIBIA
SUB-CLASS A :- STEGOCEPHALIA
- Limbs pentadactyle. Extinct.
- Skin with scales and bony plates.
Order 1. Labyrinthodontia
- Primitive tetrapods.
- Teeth large and folded similar to their crossopterygian ancestors.
Example :- Eryops (Extinct)
Order 2. Phyllospondyli
- Small salamender-like.
- Notochord and nerve cord housed in common cavity.
Example :- Branchiosaurus (Extinct)
Order 3. Lepospondyli
- Small eel-like salamanders.
- Vertebrae of a single piece.
- Probable ancestors to modem caecilians.
Example :- Diplocaulus (Extinct).
SUB-CLASS B :- LISSAMPHIBIA
- Modern amphibia.
- Teeth small. Exoskeleton absent.
- Respiration by lungs, skin and gills.
Order 1. Gymnophiona or Apoda
- Limbless elongated burrowing caecilians.
- Skull compact, limb girdles absent.
Example :- Ichthyophis, Uraeotyphlus.
Order 2. Urodela or Caudata
- Tailed amphibians.
- Gills permanent or absent in adults.
- Paired limbs present. Larval stages resemble adults.
Sub-order 1. Proteida
Sub-order 2. Cryptobranchoidea
- No gills in adults.
- Angular and prearticular of lower jaw separate.
- Permanently aquatic.
Example :- Cryptobranchus, Megalobatrachus.
Sub-order 3. Ambystomoidea
- Adults terrestrial with eyelids.
- Vertebrae amphicoelous.
Example :- Ambystoma.
Sub-order 4. Salamandroidea
- Teeth in roof of mouth behind nares in 2 long rows.
- Adults with lungs but no gills.
Example :- Triton and Triturus (Newt) Salamandra
(Salamander).
Sub-order 5. Amphimnoidea
- Body cylindrical. No eyelids.
- Adults with lungs and 1 pair of gill clefts but no gills.
Example :- Amphiuma (Congo eel).
Sub-order 6. Sirenoidea (Meantes)
- Permanent larvae. Body slender.
- Hindlegs and eyelids absent.
- Gills persistent. Forelegs small.
Example :- Siren (Mud eel), Pseudobranchus
Order 3 Anura or Salientia
- Frogs and toads. No tail.
- Eyelids and tympanum present.
- Forelimbs and hind limbs present.
- Urostyle present.
Sub-order 1 Amphicoela
- Vertebrae amphicoelous.
- Fertilization internal.
Family :- Ascaphidae
- Vertebrae connected by undivided intervertebral disc, not truely amphicoelous.
- Presacral vertebrae 9.
Example :- Ascaphus, Liapelma.
Sub-order 2. Opisthocoela
- Vertebrae opisthocoelous.
- Ribs free in adult or larva.
Family 1 :- Discoglossidae
- Disc-tongued toads.
- Eyelids present.
Example :- Alytes, Bombinator, Dlscoglassus.
Family 2 :- Pipidae
- Tongueless toads.
- Feet fully webbed.
Example :- Pipa, Xenopus.
Sub-order 3. Anomocoela
- Vertebrae procoelous or amphicoelous.
- Free ossified ribs present.
Family :- Pelopatidae
- Spadefoot toad.
- No ribs. Teeth in upper jaw.
Sub-order 4. Procoela
- Vertebrae procoelus.
- No ribs.
Family 1 :- Palaeobatrachidae
- Urostyle with 2 condyles.
- Presacral 5-8.
Example :- Palaeabatrachus
Family 2 :- Bufonidae
- True toads. No teeth
- A large paratoid gland behind eyes.
Example : –Bufo, Leptadactylus
Family 3 :- BrachycephaJidae
- Halves of pectoral girdles fused ventrally.
- Bidders’s organ absent.
Example :- Brachycephalus
Family 4 :- Hylidae
- Teeth in upper or both jaws.
- Terminal bone of each digit claw- shaped.
- Adhesive disc on toes.
Example : – Hyla, Gastrotheca
Sub-order 5. Diplasiocoela
- First 7 vertebrae procoelous. 8th vertebra amphlcoelous and 9th vertebra contains 2 condyles.
- Pectoral girdle fused to sternum. Ribs absent.
Family 1 :- Ranidae
- True frogs.
- Teeth in upper jaw.
Example :- Hoplobatrachus (Old name Rana)
Family 2 :- Rhacophoridae
- Old world frogs specialized for climbing trees. Intercalary cartilage in digits meant for climbing.
Example :- Rhacophorus
- Old world frogs specialized for climbing trees. Intercalary cartilage in digits meant for climbing.
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