Phylum Aschelminthes/Nemathelminthes: General characteristics and classification




General characteristics of Phylum Aschelminthes

  1. Gr. Askos: cavity; helmins: worms. Nema: thread, helmins: worms
  2. Habitat: They are marine or freshwater animal.
  3. Habit: They are endoparasite.
  4. Coelom: Pseudocoelomate which means they have a cavity called pseudocoel between the gut and body wall.
  5. Symmetry: bilateral
  6. Germ layer; triploblastic
  7. Grade of organization: Organ system grade
  8. They are non-segmented round worm.
  9. Their body is covered with cuticle.
  10. Digestive system: simple type
  11. The mouth is provided with hooks and suckers
  12. Respiratory system: Absent
  13. Circulatory system: Absent
  14. Nervous system: poorly developed
  15. Excretory system: Protonephridia and canals
  16. They are unisexual or dioecious animals
  17. Reproduction: sexual by gamatic fusion
  18. Fertilization: internal

Classification of phylum Aschelminthes/Nemathelminthes

Aschelminthes is classified into five classes

Class 1 Nematoda

(Nema: thread)

  • They are endoparasites
  • Body is Bilaterally symmetrical and vermiform.
  • Body covered in a complex cuticle.
  • Sexes are separate
  • Examples: Ascaris (round worm), Ancyclostoma (hook worm), Enterobius (pinworm)

Class 2 Rotifera

  • They are minute microscopic aquatic
  • Sexes are separate
  • Excretion: two protonephridia tubes
  • Examples: Brachionus, Colotheca, Philodina

Class 3 Gastrotricha

  • They are minute aquatic free living
  • Sexes are separated or united
  • Excretory organ: present or absent
  • Examples: Urodasys, macrodasys, Chaetonotus

Class 4 Kinorhyncha

  • Minute microscopic marine
  • Body is internally segmented
  • Sexes are separates
  • Development: indirect ( with larval form)
  • Examples: Echinoderes, Centroderes

Class 5 Nematomorpha

  • They are long slender un-segmented worm
  • Known as hair worm
  • Sexes are separate
  • Examples: Nectonema, Gordius

Phylum Aschelminthes/Nemathelminthes: General characteristics and classification