Chapter 6

• Class Amphibia


  • Freshwater and terrestrial
  • Paired appendages are legs
  • Skin without scales in most living species
  • With internal nares
  • Upper jaws fused to skull
  • Heart three-chambered
  • Breathing through gills, lungs, skin, and mouth cavity
  • 10 pairs of cranial nerves
  • Sexes separate
  • Fertilization mostly external, with tadpole larvae
  • Some with internal development, oviparous, ovoviviparous or viviparous
• Subclasses of Amphibia


  • Anura
  • Urodela
  • Apoda
• Anura (Toads, frogs)


  • Tailless, without neck
  • Hindlimbs usually long, feet webbed
  • 10 vertebrae
  • With eyelids
  • Adults mostly terrestrial
• Anura metamorphosis


  1. Larva (tadpole) is herbivorous, globulous and apod, with long propulsive tail and external/enveloped gills

  2. After metamorphosis, adult is carnivorous, less voluminous, with 4 legs adapted for jumping and swimming

  3. Tailless adult must breathe air to survive

  4. Eggs obligatory laid in water, external fertilization after copulation
• Urodela (Salamanders, newts)


  • Body with head, trunk, tail
  • Aquatic larvae resemble adults
  • Larvae and some adults with teeth on upper and lower jaws
  • Eyelids typically present in terrestrial adults, absent in aquatic adults
• Apoda (Gymnophiona)


  • Vermiform (1-4 dcm) body, legless
  • Short tail of same diameter as body
  • Skin with circular folds, often with embedded dermal scales
  • Eyeless
  • Small tentacles in front of nostrils
  • Tail short
  • Fertilization internal, male with copulatory organ
• Most amphibians live on land, returning to water each year to breed
• Amphibian eggs are protected by a jellylike substance and need to be laid in damp places
• Amphibians laying eggs in water normally leave them alone, but those laying eggs on land usually watch over them to protect them from predators
• Frogs and toads lay thousands of eggs in water, with frogs laying them in clumps and toads laying them in strings
• Mating behaviours


  • Male golden mantilla frogs attract mates by chirping
  • Axolotls court each other by dancing
• Frog life cycle


  1. Eggs laid in water during spring

  2. Eggs hatch into tadpoles which can swim and breathe underwater using gills

  3. After 6-9 weeks, tadpoles grow legs

  4. By 12 weeks, tadpoles change into froglets which can breathe using lungs and have a persisting tail

  5. By 12-16 weeks, adult frogs totally reabsorb their tail and breathe using lungs and skin
• Amphibian hibernation locations


  • Levant frog - under water in mud
  • Tree frog - in deep holes in trees, in soil, in ground depression, in small burrows, in crevices, or under leaves
  • Green toad - under moist objects, in small burrows, in crevices, or under leaves
  • Fire salamander - under logs or barks or small piles of branches
• Tree frogs


  • Have adhesive fingers for easy climbing
• Salamanders and toads


  • Have glands on their necks that secrete a toxic substance which forces their predators to release them
• Estivation


  During extensive periods of heat or drought, frogs can enter a period of dormancy similar to hibernation