Phylum Aschelminthes

In phylum Aschelminthes, the organisms are also called roundworms because the body is circular in cross-section. These organisms are endoparasites. They are cylindrical, unsegmented, and triploblastic animals.

Characteristics Features of Aschelminthes

The characteristics features of Aschelminthes are:

  • Habitat– These animals exist as free-living, aquatic, and terrestrial or may be found as a parasite in plants and animals.
  • Level of organization– An organ-system level of organization is found.
  • Symmetry– They are possessing a bilaterally symmetrical body. the distinct head is absent in Aschelminthes.
  • Germinal layer– Triploblastic animals
  • The body cavity or Coelom– These animals are pseudo coelomate.
  • The alimentary canal is complete.
    • A well-developed muscular pharynx is found within the alimentary canal.
    • A complete digestive system is present.
  • Excretion– Waste products are removed from the body cavity by an excretory tube through the excretory pore. In some forms protonephridia or rennet cells or giant cells as excretory organs.
  • Circulatory and respiratory system: absent.
  • The sense organs are in the form of pits, papillae, bristles, and eyespots.
  • The body is covered with a thick cuticle i.e. syncytial, it is flexible, non-living, and made up of protein (scleroprotein)
  • Reproduction– sexes are separate- dioecious
    • Dioecious- males and females are distinct. Females are longer than males.
    • Fertilization takes place internally.
    • The development may occur direct – as the young ones resemble the adult or indirectly.
Examples of Aschelminthes:

Some examples of Aschelminthes are Ascaris (roundworm), Wuchereria (Filarial worm), Ancylostoma (Hookworm), Brachiomus, Colotheca, Urodasys, Macrodasys, Echinoderes, Centroderes, etc.

Example of Aschelminthes

Example of Aschelminthes

Classification of Aschelminthes
  1. Nematoda
    • The members are endoparasites
    • The body is Bilaterally symmetrical and vermiform.
    • A complex cuticle covers the body.
    • Example: Ascaris (roundworm), Ancyclostomata (hookworm), Enterobius (pinworm)
  2. Rotifera
    • The organisms are microscopic aquatic.
    • sexes are separate
    • Excretion through protonephridia tubes.
    • Example: Brachiomus, Colotheca
  3. Gastroticha
    • They are free-living aquatic organisms.
    • Sexes are separate or united
    • Example: Urodasys, Macrodasys
  4. Kinorhyncha
    • These are marine and microscopic organisms.
    • Internally segmented body
    • separate sexes
    • Development is indirect (with the larval form)
    • Example: Echinoderes, Centroderes
  5. Nematophora
    • The body of these organisms is slender and unsegmented.
    • Also called hairworm
    • Sexes are found separate.
    • example: Nectonema, Gordius

 

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