In this article we will discuss about the classification of Phylum Amphibia.
Amphibia, as the term signifies, are the animals adapted to both land and water and as such have made a compromise between the two environments. At least, they require water for their breeding. But there are forms which do not require water medium at any stage of their life history. So, more precisely, they may be defined as cold-blooded vertebrates with a moist, glandular, smooth or rough skin.
Amphibians appeared in the remote past as far back as the Palaeozoic age. The three orders of the Palaeozoic amphibia, are extinct as such, but they appear to have left some surviving descendants.
The order Labyrinthodontia was a totally spent up Amphibia, but they were supposed to have given rise to the primitive reptiles; the Phyllospondylia gave rise to the modern Caudata and Salientia and the Lepospondylia probably gave rise to the Gymnophiona, as has been suggested by Noble.
Modern Orders:
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The modern amphibia may be divided into three existing orders:
1. Gymnophiona or Apoda.
2. Caudata or Urodela.
3. Salientia or Anura.
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Gymnophiona (Blind worms or caecilians or apoda):
1. Body elongated, worm-like.
2. Almost without tail, legs absent.
3. Presence of scales in some, embedded in the skin.
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4. Minute lidless eyes, buried deep in the head.
5. Anus opens at the posterior end of the body on the ventral surface.
6. Absence of limbs and limb girdles.
7. Males possess a rather large protrusible copulatory organ provided with hooks.
8. A protrusible tentacle, sensory in function, is present between the nostrils and the eyes.
9. Subterranean burrowing animals, tropical and subtropical in distribution.
10. Carnivorus in habit.
11. Nineteen genera are present with fifty-five species.
Example. Caecilia panchvnema.
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Caudata or Urodela:
Commonly known as salamanders and newts.
1. Body elongated.
2. Limbs present but weak in comparison to the body.
3. Presence of tail.
4. Metamorphosis very insignificant.
5. Neotenic forms are abundant, where the adults retain their larval characteristics and are commonly known as permanent larvae.
6. Presence of external gills in some.
7. Five suborders, with numerous genera and subgenera.
Examples. Water newts, Necturus maculatus, Siren lacertina, etc.
Salientia or Anura:
1. Body short and broad.
2. Hind limbs long, fore limbs short.
3. Absence of tail.
4. Head large and depressed.
5. Mouth depressed and large tympanic membranes present.
6. Metamorphosis, involving interesting changes from larval to adult condition, is well marked.
7. Absence of Neoteny.
8. Five suborders with numerous families and subfamilies. Almost cosmopolitan in distribution.
Examples. Bufo melonostictus, Rana tigrina etc.
Extinct Orders:
The Extinct orders have highly developed roofed skull.
1. Ichthyostegatia:
Primitive amphibia, known from either upper Devonian or lower Carboniferous age.
2. Labyrinthodontia:
The dentine of the teeth is typically infolded; neural arches of the vertebrae resting either on intercentrum or pleurocentrum. Lower Carboniferous to upper Trias.
3. Phyllospondyiia:
Small in size, only the neural arches of the vertebrae ossified. Lower Carboniferous to lower Permian.
4. Lepospondylia:
Neural arches with the centrum. Lower Carboniferous to lower Permian.
5. Adelospondvlia:
The centrum of the-vertebra with perforations, neural arch not fused with it. Lower Carboniferous to lower Permian.