These are also known as the jaw vertebrates. In this case the notochord is present in the embryo stage. It disappears in the adult stage and is replaced by the vertebral column. They have a pair of nostrils and a multiple semi circular canals in the ear. The fins are paired. It includes the Pisces and tetrapoda.
The Pisces are also known as true fishes. They are cold blooded and aquatic. They have fins and the process of respiration occurs by gills. The eyes have a well formed nictitating membrane. The Pisces include chondricythes, osteichthyes and placodermi. The placodermi are the earliest fishes. They do occur in the fresh water. Their body has scales which are protective in function. They do have a teeth and a bony skeleton. The fins are also present.
The tetrapoda means 4 foot organism. It excludes all the fishes. Their skin is well adapted. The mode of respiration is through lungs. They have a good set of sensory organs. It includes reptilian, mammalian, avea and amphibian. The Pisces and amphibian comes under the anamniotes group that is they do not have an amnion which is an embryonic membrane. The rest of tetrapoda like mammalian, reptilian and aves comes under amniotes. They are with amnion which is an embryonic membrane.
