Tuesday, May 19, 2015

Page 2-Biology,Amphibians cont'nd

Page2 (amphibians cont'nd)

Limbless Amphibians

Limbless amphibians are included in order Apoda and sometimes called as blind worms also(eyes poorly or less developed)
They mostly inhabit tropical and subtropical regions of Americas,Africa and Asia excluding Medagasca.They do not have fossil forms.
1)They are burrowing forms except few strictly aquatic forms.They burrow in moist ground with their strong heads.
2)They are long body worm like burrowing animals and resemble large earthworms.
3)Limbs and girdles abscent.
4)In many genera in grooves a series of small calcified scales are found unlike other amphibians. Due to linear arrangement of these scales in transverse grooves false segmentation appears in their body.
5)Eyes small functionless and covered by skin.
6)Mouth terminal.
7)They are carnivorous in food habit feeding upon small animals which are found on ground.
8)Tail either absent or very small just like Anurans.
9)Anus or Vent present at posterior end of body at ventral surface.
10)There is a characteristic sensory protrusable tentacle present on side of face between nostril and eyes in all species. It arises from a special groove in maxilla and called as facial tentacle. It compensates for sensory organ. It is protruded by being descended with blood like eractile organ and retracted by strong muscles.

11)Tympanic cavity and tympanic membrane absent. Columella also absent.
12)Kidney extends whole length of coelom.
13)Liver posteriorly constricted into many numbers of lobes.
14)Laryngotracheal chamber is prolonged into distinct trachae supported by cartilage.
 Tracheal lungs are found in these animals just like snails.Left lung is rudimentary (because body is not narrow, therefore cannot accommodate)
15)Comus arteriosus is without spiral valve.There are only 2 pairs of aortic arches i.e. systemic arch and pulmonary arch.
16)Unlike 4 branchial clefts in embryonic life of Apoda.
17)Fertilization is internal with the help of enlarged,eversible cloacal valve which serves as copulatory organ.It is armed with hooks.
Copulatory organ

18)Skull differs considerably from modern amphibians and reveals resemblances with extinct labrynthodontia i.e. limbless amphibians are primitive and retain some primitive characters mentioned below:
1.Skull solid,compact on dorsal side and have large number of bones than modern amphibian skull.
2.Cranium covered by dermal bones.
3.A pair of post orbital and post frontal bones are present.
4.Frontal and parietal are not fused and separate unlike modern amphibians.
5.Orbit is small and surrounded by bones.
6.Hyoid apparatus and dentary primitive.
7.Vertebral column also differs in many respect from modern amphibians such as
1.Number of vertebrae numerous i.e. 200 to 300 and centrum is me amphicoelus.
2.Notochord persists.
3.First vertebra devoid of odontoid process.
4.Ribs bifurcated.

20.These are either oviparous, ovoviviparous and sometimes viviparous.In oviparous forms female guards eggs in burrows after egg laying until larvae hatch out.

Continued on Page 3