Vertebrata is the largest subphylum of chordata which is characterized by the formation of cranium and vertebral column instead of notochord and brain, spinal cord instead of dorsal nerve cord. It is also called craniata due to presence of cranium and euchordata as most of the characters of chordata are expressed in vertebrata.
Characteristics features of vertebrata are:
1. Dorsal nerve cord get differentiated into brain and spinal cord.
2. Notochord is replaced by vertebral column around the spinal cord and cranium around the brain.
3. Exoskeleton and endoskeleton is differentiable.
4. Gill slits occur at least in embryo stage.
5. Heart is ventral.
6. Blood contains haemoglobin in red blood cells.
7. Paired lateral appendages ,tail, endocrine glands, autonomous nervous system and portal system ( hepatic, renal, hypophyseal) are the other traits present in subphylum Vertebrata.
Division of Vertebrata - the subphylum Vertebrata can be divided into two groups . They are –
1. Agnatha – It is a group of poikilothermic animals. Vertebrates of this group donot contains paired appendages, girdles and jaws . Mouth is sectorial. External naris is single whereas internal naris is absent. It can be divided into two – Ostracodermi (a group of fossil Agnatha, osteostracs and heterostraciare included in this category. Another group is cyclostomata. Lamprey, Hagfish are example of cyclostomata.Agnathaconsist of class cyclostomata. Characteristics of cyclostomata are –
Mouth is circular, jawless, suctorial, horny teeth, skin is smooth , without scales and has mucous glands. Notochord and imperfect vertebrae occur. Gills are without sacrificing like pouches (marsipobronchi). Heart is two chambered,RBC s are irregular, digestive system is without stomach. External naris, olfactorysac,gonad, find are unpaired. Kidneys are mesonephros,gonoduct is absent.External fertilization is occurred larval stage (ammocoete) occurs. Example- lamprey, hagfish etc.
2. Gnathostomata – The animals of this group possesses jaws ,paired appendages, pared nares and an exoskeleton. It contains different classes. They are –
Fish/Pisces: Exclusively aquatic, appendages are fins for swimming, respiration through gills, body covered by dermal scales, cold blooded gnathostomata, heart two chambered. It is of two types – Chondrichthyes (skeleton made up of cartilage), ostecthys (bony fish). Example of pisces are Catla, rohu, hilsa etc). Example of condrichthyes are shark etc.
Amphibians: Their phases of life cycle are dependent on both land and water. They are three chambered heart, cold blooded animals. Limbs are first observedin amphibian (two pairs). Thus they are first tetrapods. Example of amphibians are frog, toad etc.
Reptiles: They are tetrapodswhich have incomplete four chamber heart. Bodies are covered by dry scale, maximum of them are terrestrial.
Example of reptiles are snake, lizard , crocodile etc.
Aves: They are the first warm blooded (their body temperature remain unchanged with the change of their temperature of surrounding)animals that appeared on the earth. They have four chambered heart where the fore limbs are converted into wings. Whole body is covered by feather.
Mammals: Mammals are the most advanced and intelligent animals on the earth.They are having, mammary gland, give direct birth to the baby.