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NEET Biology
Nematoda

Frequently Asked Questions

Nematodes, or roundworms, are unsegmented, cylindrical worms found in a wide range of habitats, including soil, freshwater, marine environments, and as parasites in plants and animals.

Nematodes are pseudocoelomates, meaning they have a body cavity that is not fully lined with mesodermal tissue.

Most nematodes reproduce sexually and are dioecious (have separate sexes). Fertilization is internal, and females can lay a large number of eggs.

No, while many are parasitic, a large number are free-living and play essential roles in decomposition and nutrient cycling in ecosystems.

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ISO

Nematoda

Nematoda, commonly known as roundworms, is a phylum of unsegmented, cylindrical worms that are found in almost every environment on Earth—soil, freshwater, marine habitats, and even inside other organisms as parasites.

1.0Introduction

  • The body of members is circular in cross section and tapering at both ends, without segmentation. So also called Roundworms. 
  • Habit and habitat - Nematodes are found everywhere, they may be free living (aquatic and terrestrial) or parasites in plants and animals. 
  • Shape - They have a worm shaped long, cylindrical body with tapering ends. 
  • Symmetry - Bilateral. 
  • Germ layers – All three primary germ layers are present so animals are triploblastic. 
  • Level of organisation - Organ-system level. 


2.0Body Wall

The body wall consists of: 

  • Cuticle - Non-living, thick, and resistant to digestive enzymes of the host. 
  • Epidermis - Syncytial i.e. a continuous layer of cytoplasm having scattered nuclei. 
  • Muscle layer - Only longitudinal muscle fibres present.
  • They are pseudocoelomate animals, body cavity is there between body wall and digestive tract which is not lined by mesodermal epithelium i.e. Pseudocoel. 
  • The skeleton is absent but fluid pressure in the pseudocoelom maintains body shape. It is called Hydro skeleton.


3.0Digestive System

  • The digestive tract is complete and differentiated into mouth, pharynx, intestine and anus. 
  • Pharynx is muscular and well developed. It is used to suck the liquid food. Intestine is non-muscular. 


4.0Respiration and Excretion

  • Respiration is through the body surface by diffusion. 
  • The circulatory system is absent. 
  • The excretory system is H-shaped (Renette cell) and consists of excretory canals (Protonephridia) which removes body wastes from the body cavity through excretory pore. 
  • They develop from an embryonic "Renette cell". Excretory matter is ammonia.

5.0Nervous System and Reproduction

  • The nervous system comprises a nerve ring (Brain) and longitudinal nerve cords.
  • Reproductive systems are developed, and sexes are separate (Dioecious) i.e., male and female are distinct. 
  • Fertilization is internal and development may be direct or indirect.

6.0Examples

  • Ascaris (Roundworm) – Parasite of small intestine. 
  • Ancylostoma (Hookworm) – Parasite of small intestine. 
  • Wuchereria (Filarial worm) – Viviparous.
  • Enterobius (Pinworm or seat worm) – Parasite of large intestine

On this page

  • 1.0Introduction
  • 2.0Body Wall
  • 3.0Digestive System
  • 4.0Respiration and Excretion
  • 5.0Nervous System and Reproduction
  • 6.0Examples