4. Diversity In Living Organism
The animals belonging to class-Pisces are commonly called fishes
. They exclusively live in water
The skin of fishes is covered with scales/plates, which helps these animals to live in water
The body may be long, laterally compressed and spindle shaped or dorsiventrally flattened and disc shped. It usually consists of head, trunk and a musclular tail.
The muscular tail and fins help them to swim in water and move from one places to another.
Fishes are cold-blooded animals and their hearts have only two chambers – one auricle and one ventricle.
Fishes obtain oxygen dissolved in water and breathe through gills.
They are egg laying animals. Fertilization is external.
There are many kinds of fishes. They have been broadly grouped under three categories. Cyclostoma :
The round mouthed fishes. Examples, The hag fish, the lamprey. Chondrichthyes :
The cartilaginous fishes. Examples Scoliodon (dog fish or the Indian Shark), sting ray, electric ray (Torpedo) (figure). Osteichthyes :
The bony fishes. Examples, Labio rohita (Rohu), Hippocampus (Sea horse), Tuna, etc. Some cartilaginous fishes A. Scoliodon (dog fish or the Indian shark); B. Sphyrna (hammer headed shark); C Pristis (Saw-fish); D. Torpedo (the electric ray); E. Sting ray