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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