properties of amphibians

Amphibians

Natural history

  • The amphibians (the vertebrates with dual life) were the first vertebrates to invade land, but they aren’t fully dependent to terrestrial life.
  • They occur in fresh water and moist land but no marine forms.  Some frogs live on trees. E.g. Hyla

Life phases

  •  The amphibians undergo metamorphosis and generally have two phases in their life; the larval form and the adult.
  • Larval stage, called tadpole, is fish-like, lives in water, swim with a tail.
  • Adult stage is terrestrial, moves about with limbs supplied with webs.

General characteristics

  • They are poikilothermic (cold blooded) animals and most forms hibernate in winter and aestivate in summer.
  • The carboniferous period is regarded as the age of amphibians.
  • The body may be long and narrow, short and broad, depressed or cylindrical.
  •  The body may be divisible into head, trunk and tail (salamander) or only into head and trunk (frog).

Appendages

  • There are two pairs of pentadactyl limbs, each with 4-5 or fewer digits.
  •    The digits are without claws, nails or hooves, and often with webs.
  •      The skin is without scales, smooth, moist, rich in multicellular mucous or poison glands.
  •     Skull is flat and dicondylic (with two occipital condyles).

Digestive system

  • The mouth is large and armed with acrodont and vomerine teeth in the upper jaw.
  • They have a true tongue and it is soft, mucous-coated and attached at the front end (protrusible tongue).
  • Distinct liver and pancreas are present.  Alimentary canal leads into the cloaca.

Respiratory system

  • Tadpoles respire through gills as they live in water.
  • Adults respire with lungs, lining of buccopharyngeal cavity and skin.
  • Some forms have vocal cords.

Circulatory system

  • Circulatory system is closed and the heart is three chambered: two auricles and one ventricle.
  •  The ventricle pumps the mixed blood; sinus venosus and truncus arterisus are present.
  • Well-developed renal portal system and hepatic portal system are present.
  • RBCs are oval, biconvex and nucleated.

Excretory system

  • Kidneys are pronephric in larvae and mesonephric in adult.
  • Waste material is either urea (in ureotelic or tailless forms) or ammonia (in ammoniotelic forms or larvae and tailed forms).
  • Urinary bladder is present.

Reproductive system

  • The gonoducts lead into the cloaca.
  • Male lack a copulatory organ.
  • Fertilization may either be external or internal.
  • Most forms are oviparous; eggs have a coat of jelly and usually laid in water.

Sense organs

  • The olfactory sacs are paired and dorsal.
  • Eyes often have movable lids.
  • Middle ear with a single auditory ossicle is present in addition to the internal ear.
  • Tympanum covers the middle ear but there is no external ear.
  • Lateral-line sense organs are present in the larvae and in aquatic forms but absent in terrestrial forms.
  • There are 10 pairs of cranial nerves and 9-10 pairs of spinal nerves.

Leave a Comment