a. Chondrichthyes and Osteichthyes

b. Urochordata and cephalochordate

1.Chondrichthyes

●mainly marine and their body is streamlined. 

●cartilaginous endoskeleton.

●Examples are scoliosis and Trygon

2.Osteichthyes

● both marines as well as freshwater  

●streamlined body. 

●the endoskeleton is bony.

●Examples are •Marine-Hippocampus (Sea horse),

• Freshwater: Labeo (Rohu), •Aquarium: Betta (Fighting fish)

b) Urochordata and cephalochordate

●In urochordates, notochord is present only in the larval tail 

●But in cephalochordates, notochord extends from head to tail region and is persistent throughout the life span .

●Examples – Urochordates-Ascidia, Salpa, Cephalochordates: Branchiostoma