Class Fishes:
Charachterisitics, Classificiaon and Examples;

1. Fishes are first evolved in silurian period of palaeozoic era.
2. They increased their number in Devonian period. Devonian Period Is Called Age of Fishes.
3. Fishes are aquatic; cold blooded vertebrates.
4. It has a spindle shaped body. It is helpful in swimming.
5. The body is covered by scales.
6. Respiration is by gills. Gills are the extensions of the pharynx.
7. On the head a pair of eyes is present.
8. On the lateral sides of the body LATERAL LINE SENSE organs are present.
9. They detect the pressure changes of water.
10. Pelvic and pectoral fins are paired.
11. Dorsal and ventral fins are unpaired. They maintain balance in water. They are useful for locomotion.
12. The digestive system is well developed.
13. The nervous system contains brain and spinal cord. Brain is small & it will not occupy the entire cranial cavity.
14. 10 pairs of cranial nerves are present.
15. Many fishes are oviparous. Some fishes are viviparous.
16. In the development of fishes amnion is not developed.