Division Vertebrata (Craniata)
This group is characterized by the presence of brain case or cranium and vertebral column. The notochord is an embryonic structure gets replaced by a vertebral column which forms the chief skeletal axis of the body. They have ventral muscular heart with two, three or four chambers. The locomotor organs may be ns or limbs. Excretion and osmoregulation are carried out by a pair of kidneys. They exhibit sexual dimorphism.
Fishes are poikilothermic, aquatic vertebrates with jaws. The body is streamlined. It is differentiated into head, trunk and tail. Locomotion is by paired and median ns. The body has a covering of scales. Body muscles are arranged into segments called myotomes. Respiration is performed by gills. Gill slits are 5-7 pairs. They are covered by an operculum. The heart is two chambered with an auricle and a ventricle. Lateral line sense organs are well developed.