In phylum Aschelminthes, the organisms 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:
- Habitat– These animals existing 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 with the alimentary canal.
- A complete digestive system is present.
- Excretion– Waste products 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.
Some examples of Aschelminthes: Ascaris (roundworm), Wuchereria (Filarial worm), Ancylostoma (Hookworm), Brachiomus, Colotheca, Urodasys, Macrodasys, Echinoderes, Centroderes, etc.
Classification of Aschelminthes
- The members are endoparasites
- The body is Bilaterally symmetrical and vermiform.
- A complex cuticle covers the body.
- Example: Ascaris (roundworm), Ancyclostomata (hookworm), Enterobius (pinworm)
- The organisms are microscopic aquatic.
- sexes are separate
- Excretion through protonephridia tubes.
- Example: Brachiomus, Colotheca
- They are free-living aquatic organisms.
- Sexes separate or united
- Example: Urodasys, Macrodasys
- These are marine and microscopic organisms.
- Internally segmented body
- separate sexes
- Development is indirect (with the larval form)
- Example: Echinoderes, Centroderes
- The body of these organisms is slender and unsegmented.
- Also called hairworm
- Sexes are found separate.
- example: Nectonema, Gordius
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