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Wednesday, September 30, 2020

Phylum Hemichordata - NEET-Biology

 Phylum Hemichordata

Fig: Acorn worm (Hemichordate)

  • Hemichordate = half chordate.
  • These are not classified as true chordates, although they are closely related.
  • Some DNA-based studies evolution suggest that hemichordates are actually closer to echinoderms than to true chordates.
  • It was earlier considered as a sub-phylum under the phylum Chordata. 
  • But, now it is placed under a separate phylum under non-chordates.

Important characteristics:

  • Exclusively marine.
  • The body is cylindrical & is composed of an anterior proboscis, a collar & a long trunk.
  • Notochord present which allows & endodermal in origin (termed stomochord).
  • Notochord occurs only in the anterior end of the body. It is called the buccal diverticulum.
  • Open circulatory system.
  • Perform sexual reproduction.
  • Sexes are separate.
  • Fertilization is external.
  • Development is indirect.
  • Example: Balanglossus (Tongue worm), Ptychodera & Saccoglossus.
Fig: Balanoglossus (Tongue worm)



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