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Class Chondrichthyes:

1.      Classified under the division Gnathostomata, which is further sub-divided into two super class, Pisces and Tetrapoda. The first class under the super-class Pisces is Chondrichtyes

2.      Marine animals with cartilaginous endoskeleton and a streamline body designed to swim freely in water

3.      Notochord is present throughout its life cycle and mouth is present ventrally.

4.      Presence of separate gills without operculum (gill cover)

5.      Tough skin with the presence of minute placoid scales. A modification of these scales are teeth which are oriented backwards

6.       Presence of powerful jaws which prey on other small fishes

7.      These animals need to swim constantly as they lack air bladder.

8.      Presence of two-chambered heart with one auricle and one ventricle.

9.      Cold-blooded animals, also known as Poikilothermous, as they lack the capacity to regulate their body temperature.

10.  Characteristic features – Some animals have electric organs (Eg. Torpedo), which some have poisonous sting (Eg., Trygon)

11.  Organisms are dioecious, with internal fertilization. Organisms are viviparous.

12.  Example of organisms belonging to class Chondrichcytes – Pristis (Saw fish), Trygon (Sting ray), Scoliodon (Dog fish)

 

A.     Scoliodon                    B. Pristis

 

Class Osteichthyes:

1.      Includes both marine and fresh water fishes

2.      Streamlined body with bony endoskeleton

3.      Four pairs of gills on both sides of the body which are covered by operculum

4.      Presence of air bladder which regulates buoyancy

5.      Cold-blooded animals with two-chambered heart

6.      Animals are dioecious with external fertilization and direct development. Animals are usually oviparous.

7.      Examples of organisms belonging to this class -  Marine – Hippocampus (Sea Horse), Fresh water – Catla (katla), Aquarium – Pterophyllum (Angel fish)

 

A.    Hippocampus                                     B. Catla

Class Amphibia:

1.      Terrestrial and aquatic habitat animals, hence the name (Greek: Amphi – dual; bios- life)

2.      Body is divided in to two parts – head and trunk. Tail may be present in larval stages

3.      Most of them have two pairs of limbs. Scales are absent. Skin is moist. Eyes covered by eyelids.

4.       Ear is represented by tympanum.

5.      Respiration is by lungs and skin (on land) and via gills (within water)

6.      Alimentary canal, reproductive and urinary tracts open into a common chamber called cloaca which opens into the exterior surface of the body.

7.      Cold-blooded animals with three chambered heart (2 auricles and 1 ventricle)

8.      Animals are oviparous with external fertilization and direct/indirect development.

9.      Organisms belonging to class Amphibia – Rana (Frog), Salamandra (Salamander), Ichthyophis (Limbless Amphibia)

 

A.     Salamandra                B. Rana

Various Classes of The Sub-Phyla Vertebrata Homework Help