What are the various Classes of Chondrichthyes?
1. Classified under the division Gnathostomata, which is further subdivided into two superclasses, Pisces and Tetrapoda.
The first class under the super-class Pisces is Chondrichthyes
2. Marine animals with cartilaginous endoskeletons and streamlined bodies designed to swim freely in water
3. The notochord is present throughout its life cycle and the 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 is teeth which are oriented backward
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 a 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), while some have a poisonous sting (Eg., Trygon)
11. Organisms are dioecious, with internal fertilization. Organisms are viviparous.
12. Example of organisms belonging to class Chondrichthyes – Pristis (Sawfish), Trygon (Stingray), Scoliodon (Dogfish)
A. Scoliodon B. Pristis
What is the Class Osteichthyes?
1. Includes both marine and freshwater fishes
2. Streamlined body with the bony endoskeleton
3. Four pairs of gills on both sides of the body which are covered by an operculum
4. Presence of air bladder which regulates buoyancy
5. Cold-blooded animals with a 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), Freshwater – Catla (Katla), Aquarium – Pterophyllum (Angelfish)
A. Hippocampus B. Catla
What is the Class Amphibia?
1. Terrestrial and aquatic habitat animals, hence the name (Greek: Amphi – dual; bios- life)
2. Body is divided into two parts – head and trunk. The 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. The ear is represented by a tympanum.
5. Respiration is by lungs and skin (on land) and via gills (within the water)
6. Alimentary canal, reproductive and urinary tracts open into a common chamber called the cloaca which opens into the exterior surface of the body.
7. Cold-blooded animals with three-chambered hearts (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