4. Kingdom Animalia - part 11 - Phylum : Hemichordata

 


4. Kingdom Animalia - part 11 - Phylum : Hemichordata


Phylum : Hemichordata (Hemi : Half, Chordata : Rod)

  • e.g. Balanoglossus, Saccoglossus.
  • Earlier, this Phylum was considered as sub-phylum of Chordata because buccal diverticulum was considered as notochord. But, now it is placed as a separate phylum of Non-chordata. 
  • These are exclusively marine animals, usually living at the bottom of sea in burrows. 
  • Mostly these are free living but the animals like Rhabdopleura are sedentary. 
  • Body is soft, vermiform, unsegmented and divided into three parts -
  1. proboscis
  2. collar and 
  3. trunk.


  • Buccal cavity gives rise to rod-like buccal diverticulum which is considered as notochord by some scientists.
  • Alimentary canal is complete, straight or 'U' shaped. 
  • Respiration occurs by numerous gills, arranged in two longitudinal rows, present in the pharyngeal region. 
  • Gills open by gill slits.
  • Circulatory system is simple and open type. 
  • Excretion occurs with the help of glomerulus. 
  • Nervous tissue is embedded in epidermis on both dorsal and ventral sides.
  • The sexes are separate (sometimes bisexual). 
  • Fertilization is external and development is indirect through free swimming larva. 
  • This phylum is the connecting link between nonchordata and chordata.

Do u know ?

  • Notochord is flexible rod-like structure of vacuolated cells.
  • It is located along the dorsal side of chordate embryos. 
  • It gives support to the body and provides attachment to muscles.

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