4. Kingdom Animalia - part 06 - Phylum : Aschelminthes

 

4. Kingdom Animalia - part 06 - Phylum : Aschelminthes


Phylum : Aschelminthes (ascus-sac,helminth-worm) / Nemathelminthes (nema-thread) :

  • e.g. Ascaris (Roundworm), W uchereria (filarial worm), Ancylostoma (hook worm).
  • These are mostly parasitic, few forms are free-living. 
  • Body is long, cylindrical, thread like, circular in cross-section, hence are called round worms. 
  • They are triploblastic, bilaterally symmetrical, pseudocoelmate, with tube within tube body plan. 
  • Body is covered by tough and resistant cuticle. 
  • Body wall has longitudinal muscles but no circular muscles. 
  • Alimentary canal is complete with mouth and anus at opposite ends. 
  • Pharynx is well developed and muscular. 
  • Excretion takes place by canals or gland cells. 
  • Excretory products are eliminated through excretory pore. 
  • Nervous system has nerve ring and nerves. 
  • Animals are unisexual i.e. sexes are separate. 
  • Animals like Ascaris shows sexual dimorphism. 
  • Usually female is longer and broader and have straight posterior end. 
  • Male is shorter and narrower and has curved posterior end with a pair of penial setae for copulation. 
  • Fertilization is internal.
  • Development may or may not include larval stage.

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