18Amphibia

πŸ“š
CLASS AMPHIBIA
β–’ Meaning and General Position:
❖ Meaning: Amphi = both; bios = life
❖ Habit: Living both in water and land
❖ Vertebrate Rank: Smallest class of vertebrates in number of species
❖ Origin: Originated during Devonian period from Stegocephalia
❖ Dominance: Dominated during Carboniferous period
❖ Age: Carboniferous period = Age of amphibians
❖ Marine Amphibians: No amphibian is marine
❖ Examples by Habitat:

Table 1: Amphibian Habitat

Habitat
Example
Arboreal
Hyla
Terrestrial
Toad
Aquatic / semi-aquatic
Frog, salamander larva
β–’ External Morphology:
❖ Body: Head distinct; trunk elongated
❖ Neck and Tail: May be present or absent
❖ Limbs: Usually two pairs; tetrapod
❖ Limbless Form: Seen in Apoda / Gymnophiona
❖ Digits: Toes 4–5 or less; pentadactyl type
❖ Fins: Paired fins absent; median fins may be present without fin rays
❖ Skin: Soft, moist, glandular and vascular
❖ Pigment Cells: Chromatophores present
❖ Exoskeleton: Generally absent
❖ Dermal Scales: Sometimes concealed dermal scales present, especially in caecilians
β–’ Skeleton:
❖ Endoskeleton: Bony
❖ Skull: Dicondylic with two occipital condyles
❖ Vertebrae: Usually procoelous
❖ Axis Vertebra: Absent
❖ Sacral Vertebra: Single sacral vertebra present
❖ Cranial Nerves: 10 pairs
β–’ Digestive System:
❖ Mouth: Large
❖ Teeth: Homodont, polyphyodont and acrodont
❖ Tongue: Protrusible
❖ Alimentary Canal: Terminates into cloaca
β–’ Respiration:
❖ Adult Respiration:
  • β€’
    Lungs
  • β€’
    Skin
  • β€’
    Buccal lining
❖ Larval Respiration: Larvae and certain aquatic forms respire by external gills
❖ Skin Respiration: Favoured by moist, vascular and glandular skin
β–’ Circulatory System:
❖ Heart: 3-chambered
❖ Heart Chambers: 2 auricles + 1 ventricle
❖ Sinus Venosus: Present
❖ Portal Systems: Renal and hepatic portal systems well developed
❖ Circulation: Double circulation
❖ Ventricle: Pumps mixed blood
❖ RBC: Large, oval, biconvex and nucleated
β–’ Excretory System:

Table 1: Kidney and Excretion

Stage / Animal
Excretory Organ / Product
Larva
Pronephros
Adult amphibian
Mesonephros
Most amphibians
Ureotelic
Salamanders
Ammonotelic
Frog tadpole functional kidney
Pronephros
β–’ Sense Organs:
❖ External Ear: Absent
❖ Middle Ear: Single rod-like ossicle present
❖ Ear Ossicle: Columella auris and stapedial plate
❖ Lateral Line: Present in larval forms and some aquatic adults
β–’ Reproduction and Development:
❖ Sex: Sexes separate
❖ Male Copulatory Organ: Absent in most amphibians
❖ Fertilization: Mostly external in frog; sometimes internal in salamander
❖ Female: Mostly oviparous
❖ Egg: Large with moderate amount of yolk; mesolecithal
❖ Extraembryonic Membranes: Absent; anamniota
❖ Development: Usually indirect
❖ Larva: Tadpole larva metamorphoses into adult
❖ Body Temperature: Cold-blooded / poikilothermic / ectothermic
❖ Seasonal Sleep: Hibernate in winter and aestivate in summer
β–’ Classification:

Table 1: Classification of Amphibia

Group
Status / Examples
Subclass Stegocephalia
Extinct amphibians
Subclass Lissamphibia
Living amphibians
Order Gymnophiona / Apoda
Caecilians; limbless amphibians
Order Urodela / Caudata
Salamanders and newts
Order Salientia / Anura
Frogs and toads
β–’ Order Gymnophiona / Apoda:
❖ Common Name: Caecilians / blindworms
❖ Body: Limbless, blind, elongated, worm-like and burrowing
❖ Skin: Dermal scales embedded in skin
❖ Male: Protrusible copulatory organs present
❖ Examples:
  • β€’
    Ichthyophis
  • β€’
    Uraeotyphlus
❖ Ichthyophis: Limbless amphibian showing parental care; no tongue
❖ Important Point: Limbless amphibians are sometimes called blindworms
β–’ Order Urodela / Caudata:
❖ Common Examples: Newts and salamanders
❖ Body: Lizard-like with distinct tail and paired limbs
❖ Tympanum: Absent, gills permanent or lost in adult
❖ Male: Without copulatory organs
❖ Limbs: Forelimbs and hindlimbs of same size with 4 digits
❖ Examples:
  • β€’
    Salamander
  • β€’
    Triturus
  • β€’
    Necturus
  • β€’
    Ambystoma
❖ Ambystoma: Tiger salamander found in USA
❖ Axolotl: Larva of Ambystoma; found in North America and Mexico
❖ Neoteny / Paedogenesis: Retention of larval characters even after sexual maturity
β–’ Order Salientia / Anura:
❖ Common Name: Frogs and toads
❖ Tail: Absent in adult; present in larval stage
❖ Limbs: Legs longer than hands
❖ Adult Gill: Absent
❖ Eyelids: Well formed
❖ Tympanum: Present
❖ Skin: Loose-fitting, scaleless
❖ Mandible: Toothless
❖ Examples:
  • β€’
    Rana
  • β€’
    Bufo
  • β€’
    Alytes
  • β€’
    Rhacophorus
  • β€’
    Xenopus
❖ Frog:
β—‰ Exoskeleton: Scales absent
β—‰ Diaphragm: Absent
β—‰ Toad Difference: Frog differs from toad by absence of warts
β—‰ Male Frog: Croaks louder due to vocal sacs
β—‰ Ear: No pinnae
β—‰ Digits: 4 fingers in hands and 5 toes in legs
β—‰ Skin Glands: Mucous and poisonous glands
β—‰ Excretion: Ureotelic
β—‰ Seasonal Sleep: Aestivates in summer and hibernates in winter
❖ Special Examples:

Table 1: Special Amphibian Examples

Animal
Important Point
Bufo marinus
Poisonous amphibian
Poison gland of toad
Modified parotid gland
Alytes
Midwife toad; male shows parental care
Bombinator
Warning coloration
Rana goliath
Largest frog
Hyla
Arboreal green frog
Rhacophorus
Flying frog
Xenopus
Used in diagnosis of human pregnancy
Phyllobates limbatus
Smallest frog found in Cuba
Discoglossus
Fire-bellied toad
Phrynosoma
Horned toad; actually a lizard, not an amphibian
β–’ High-Yield Competitive Points:

Table 1: Must Remember

Question Clue
Answer
Amphibia meaning
Both life
Origin period of amphibians
Devonian
Age of amphibians
Carboniferous
Smallest vertebrate class by species
Amphibia
Marine amphibians
Absent
Skull type
Dicondylic
Vertebrae
Procoelous
Sacral vertebra
Single
Heart
3-chambered
RBC
Oval, biconvex, nucleated
Larval kidney
Pronephros
Adult kidney
Mesonephros
Extraembryonic membranes
Absent / anamniota
Larva
Tadpole
Apoda example
Ichthyophis
Urodela example
Salamander
Anura example
Frog
Neoteny example
Axolotl larva of Ambystoma
Largest frog
Rana goliath
Flying frog
Rhacophorus
Pregnancy test amphibian
Xenopus
Q1.
The word Amphibia means
Q2.
Amphibians originated during which geological period?
Q3.
The Carboniferous period is called the age of
Q4.
Which of the following habitats is absent in Amphibia?
Q5.
Amphibian skin is mainly
Q6.
The skull of amphibians is
Q7.
The vertebrae of Amphibia are generally
Q8.
How many sacral vertebrae are present in amphibians?
Q9.
The heart of adult amphibians is
Q10.
Amphibian erythrocytes are
Q11.
Functional kidney of adult amphibians is
Q12.
Functional kidney of frog tadpole is
Q13.
Most amphibians are
Q14.
Extraembryonic membranes in amphibians are
Q15.
The larva of frog is called
Q16.
Amphibians are cold-blooded animals, also called
Q17.
Class Amphibia is divided into two subclasses
Q18.
Order Gymnophiona is also called
Q19.
Ichthyophis belongs to
Q20.
Which amphibian shows parental care and has no tongue?
Q21.
Urodela or Caudata includes
Q22.
Axolotl is the larva of
Q23.
Retention of larval characters even after sexual maturity is called
Q24.
Adult frogs and toads belong to order
Q25.
Tail in Anura is
Q26.
Which structure is absent in frog?
Q27.
A frog differs from a toad mainly by absence of
Q28.
The largest frog is
Q29.
The flying frog is
Q30.
Which amphibian was used in diagnosis of human pregnancy?