Aschelminthes Characteristics and Classification | Free Biology Notes

Aschelminthes Characteristics and Classification

After reading this article you will learn about Aschelminthes Characteristics and Classification

Aschelminthes General Characteristics

  • Habit & habitat:- Aquatic and terrestrial. Free living or parasitic in plants & animals
  • Aschelminthes are commonly referred to nematodes, roundworms & threadworms
  • Nematodes have long, cylindrical body with tapering ends without segmentation
  • Anterior end does not show distinct head
  • Body wall consist of:- Cuticle – Non living and resistant to digestive enzymes of host. Epidermis –
  • Syncytial epidermis beneath cuticle. Muscle layer – Only longitudinal muscle fibres present
  • Skeleton system absent but fluid pressure in the psedocoelom maintains body shape called hydroskeleton
  • Digestive system is complete and differentiated into mouth, Pharynx, Intestine and anus
  • Respiration is through body surface by diffusion
  • Excretory system consist of excretory canals which remove body waste through excretory pores.
  • Nervous system comprises of nerve ring and longitudinal cords
  • Sense organs
    • Papillae – a receptor for the sense of touch
    • Amphids – Chemoreceptor’s long the cuticle
    • Phasmids – Chemoreceptor’s near the anus
    • Ocelli – Eyespots found in aquatic nematodes
  • Reproductive system is developed and saxes are separate
  • Sexual dimorphism is present
  • Male is smaller than female and curved from its caudal end
  • Male has pineal setae for copulation. Genital tract joins with digestive tract to form cloaca
  • Female is larger than male and straight at both ends. Genital and digestive tract open independently. Female lays a large number of fertilized eggs
  • Fertilization is internal and development may be direct or indirect

Classification of Aschelminthes

Class 1. Phasmidia

  • Mostly parasite
  • Phasmids present
  • Excretory system developed
  • E.g. Wuchereria, Ascaris

Class 2. Aphasmidia

  • Mostly free living
  • Phasmids absent
  • No excretory system
  • E.g. Trichinella, Paramermis

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