describe the Phylum chordata and its classes
Answers
Phylum Chordata belongs to the Kingdom Animalia and includes all the vertebrates, i.e., animals with a backbone, and several invertebrates, i.e., organisms without a backbone. They possess a bilaterally symmetrical body and are divided into three different sub-phyla
classes:
Urochordata
The adults are fixed to the substratum.
It is also known as Tunicate because the body of an adult is enclosed within a tunic made up of cellulose -like substance known as tunicin.
Notochord can be seen only in the larval stage and disappears in the adults.
The nerve cord present in larva is replaced by a dorsal ganglion in adults.
The larva can move and undergoes a metamorphosis.
For e.g., Ascidia, Salpa, Doliolum.
Cephalochordata
The atrium is present.
Motile adult and larval stage.
The tail is present throughout life.
They show progressive metamorphosis.
The notochord is found throughout life.
Numerous well-developed pharyngeal gill slits are present.
For e.g., Lancelets possess the notochord and nerve cord throughout their life. However, they lack the brain and bony vertebral column like Branchiostoma.
Vertebrata
The characteristic features of vertebrates include:
These are advanced chordates and have cranium around the brain.
The notochord is replaced by a vertebral column in adults. This is why it is said that ‘all vertebrates are chordates but all chordates are not vertebrates’.
A high degree of cephalization is observed.
The epidermis is multi-layered.
They consist of three types of muscles-striped, unstriped and cardiac.
They have a well-developed coelom.
The alimentary canal is complete.
The heart is three or four-chambered.
They have well-developed respiratory and excretory systems.
Endocrine glands are present in all.
They are unisexual and reproduce sexually, hagfish being an exception.
For e.g., humans.
Subphylum Vertebrata is further classified into seven classes. They are:
Cyclostomata
Chondrichthyes
Osteichthyes
Amphibia
Reptilia
Aves
Mammalia
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The most distinguishing feature of a Chordata is that it has a bundle of nerves and cartilage supporting these nerves all along the back, also known as the spine. ... The classes of the Phylum Chordata are the Amphibia, the Reptilia, the Fish, the Birds, and the Mammalia.