Amphibia General Characteristics, Classification and Examples | Free Biology Notes

After reading this article you will learn about Amphibia General Characteristics, Classification and Examples

Amphibia General Characteristics

• They live in aquatic and terrestrial habitats
• First chordate animals which came out of water but are not able to live on land permanently, as they depend on water for their reproduction
• They are cold blooded animals
• These animals undergo hibernation (winter sleep) or aestivation (summer sleep) to prevent themselves from extreme cold and heat and to overcome unfavourable condition
• Body is divided into head and trunk. Tail may be present or absent
• Two pairs of limbs present. Fore limbs have 4 digits and hind limbs have 5 digits
• Skin is moist, glandular, smooth and scaleless
• Numerous mucus glands are found on skin, which help in moistening the skin
• Cutaneous respiration it means respiration occur through moist skin
• Pigment cells are found called as chromatophore for colouration
• Few amphibians have ability to change colour by expansion and contraction of pigment cells. This phenomenon is called metachrosis
• Digestive system is well developed, complete alimentary canal along with digestive glands are present
• Alimentary canal, urinary tract and reproductive tract open in a common chamber called cloaca
• Eyes have eyelids
• Respiration by gills, skins, lungs or Bucco pharyngeal cavity
• Heart is 3 chambered 2 auricle and one ventricle and double circulation present
• They are mostly ureotelic
• Ear consist of internal and middle ear. Tympanum covers the middle ear.
• Ten pairs of cranial nerves are present
• Sexes are separate. Fertilisation is external. They are oviparous and development is indirect
• Some members shows neoteny in which larva mature and start reproduction

Classification of Amphibia

The Amphibians are divided into three orders. The classification of amphibia is given below:

Order 1. Apoda or Gymnophiona

• These are primitive limbless amphibians
• Body worm like and burrowing in nature
• Scales present but embedded in skin
• Male has protrusible copulatory organ
• Eye without eye lids
• Parental care found

Examples of Apoda

Ichthyophis

• Female coil around eggs and provide parental care
• Tympannum absent
• Also called blind and deaf worm

Order 2. Urodela or Caudata

• Body is distinctly divided into head, trunk and tail
• They are called urodella as tail is found life long
• Two pairs of equal sized limbs present
• Copulatory organ absent in male
• Some members show neoteny
• Scales are absent in them

Examples of Urodela

Necturus (Water dog or mud puppy)

• It show permanent neoteny
• Tympanum is absent
• There are 3 pairs of external gills
• Tail bears caudal fin and they are nocturnal

Ambystoma (Tiger salamander)

• It exhibits the phenomenon of neoteny
• When there is iodine deficiency in water, the axolotl don’t change into an adult

Order 3. Anura or Salientia

• Tailless amphibian
• Eyes with eyelids (lover lid movable and upper lid immovable)
• Middle ear and tympanum present
• Body divided into head and trunk. neck absent.
• Fertilization is external and development through tadpole larva
• Forelimb small and hind limb long

Examples of Anura

Hyla (Tree Frog)

• It is adopted for life in trees
• Large vocal sac present

Rhacophorus (Flying frog)

• Webs developed between digits
• parental care found

Bufo (Toad)

• It inhibits on moist and dark shady places
• It bears poisonous gland (Parotoid gland)