4. Kingdom Animalia - part 12 - Phylum : Chordata

 

4. Kingdom Animalia - part 12 - Phylum : Chordata


Phylum : Chordata


  • Chordates are characterised by -
  1. presence of cartilagenous notochord at least in early embryonic life
  2. presence of gill slits in the pharyngeal (neck) region
  3. presence of hollow, dorsal nerve cord running through out the length of body and 
  4. ventral heart.


  • Phylum Chordata is divided into three subphyla-
  1. Urochordata
  2. Cephalochordata and
  3. Vertebrata. 
  • Urochordata and Cephalochordata are collectively called Protochordates.


a. Subphylum : Urochordata or Tunicata :


  • e.g. Herdmania, Salpa, Doliolum.
  • These are also called as tunicates or ascidians. 
  • They are exclusively marine. Body is soft and covered by 'test' or 'tunic' which is made up of tunicine. 
  • Notochord is present only in the tail of larva, hence the name, urochordata.
  • Notochord is lost during metamorphosis.
  • Pharynx has many gill slits. 
  • Closed circulatory system is present. 
  • Development is indirect.



b. Subphylum : Cephalochordata :


  • e.g. Branchiostoma (Amphioxus or Lancelet) 
  • They are exclusively marine. 
  • These are also called as lancelet, which are small fishlike animals that rarely exceed 5 cm in length.
  • Lancelets partly live burried in soft marine sediments. 
  • Notochord extends throughout the length of body and present throughout the life. 
  • Myotomes (muscle blocks) are present. 
  • Post-anal tail is present. 
  • Closed circulatory system is present. 
  • Blood is without pigment.


c. Subphylum : Vertebrata :


  • In these chordates, notochord is replaced by cartilaginous or bony vertebral column. 
  • It is divided into two divisions - 
  1. Agnathostomata (no jaws) and 
  2. Gnathostomata (jaws present).


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