Notes on Nemathelminthes | Grade 11 > Biology > Introduction to kingdom Animalia | KULLABS.COM

Nemathelminthes

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Example of Phylum Nemathelminthes
source:www.kullabs.com
fig:Example of Phylum Nemathelminthes

Nemathelminthes is composed of two words i.e. nematodes which mean thread and helminths which mean worm. Gegenbaur coined the term nemathelminths in 1859.

General characteristic features of Nemathelminthes:

  • They are cylindrical, elongated, unsegmented and worm-like.
  • They are mostly parasitic and some are free living found in soil and water.
  • They are triploblastic.
  • They are bilaterally symmetrical.
  • Coelom is pseudo coelom type i.e body cavity s lined by mesodermal layer.
  • Nutrition is a holozoic type.
  • The alimentary canal is complete and straight. Mouth is terminal surrounded by lips.
  • The respiratory system is absent. Respiration is anaerobic type in parasitic forms only.
  • Transport of fluid nutrients takes place with the help of hydro lymph or pseudocoelomate fluid.
  • The body is covered with the thick non-living cuticle.
  • It consists of lateral excretory ducts which collect the excretory substances and expel out through the anus.
  • It consists of nerve ring ana a longitudinal nerve cord. sense organs are poorly developed.
  • They are unisexual or dioecious and sexual reproduction takes place.
  • Fertilization is internal.
  • Development may be direct or indirect with some larval stages.
  • The body has not the distinct head.

Classification:

It is classified into two classes on the basis of presence and absence of amphids.

Trichuris
source:ruby.fgcu.edu
fig:Trichuris

Phasmida:

  • Caudal sense organ(phasmid) is present.
  • Most of them are parasitic forms.
  • Example: Ascaris, Trichuris.
Rotifers
source:www.microimaging.ca
fig:Rotifers

Aphasmida:

  • Caudal sense organ is absent.
  • Most of them are free-living forms.
  • Amphids or anterior sensory organs are present.
  • Example: Dorylaimus, Rotifers.



  • Nemathelminthes is composed of two words i.e. nematoswhich means thread and helminthes which means worm. 
  • They are cylindrical, elongated, unsegmented and worm like.
  • They are mostly parasitic and some are free living found in soil and water.
  • Body is covered with thick non living cuticle.
  • Fertilization is internal.
  • Development may be direct or indirect with some larval stages.
  • Body has not distinct head.
  • Development may be direct or indirect with some larval stages.
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