• Aschelminthes, also known as "pseudocoelomates," are a diverse group of small, worm-like, bilaterally symmetrical invertebrates.
  • They are characterized by their simple body structure and the presence of a pseudocoelom, which is a fluid-filled body cavity not completely lined by mesoderm.


  1. Bilateral Symmetry: Aschelminthes exhibit bilateral symmetry, meaning they have a left and right side that are mirror images of each other.

  2. Pseudocoelom: They possess a pseudocoelom, which is a body cavity located between the endoderm and mesoderm. It is not fully lined with mesoderm, unlike the true coelom found in higher animals.

  3. Body Shape: Aschelminthes have a simple, elongated, worm-like body shape.

  4. Digestive System: They have a complete digestive system with a mouth and an anus. Some may have specialized feeding structures like pharyngeal jaws or stylets.

  5. Excretory System: Excretion is primarily performed by protonephridia (excretory tubules).

  6. Reproduction: Aschelminthes can reproduce both sexually and asexually, depending on the species. Some are hermaphroditic (having both male and female reproductive organs).

  7. Larval Forms: Many Aschelminthes have larval stages with distinct morphological features.

Classes of Aschelminthes:

  1. Nematoda (Roundworms):

    • Nematodes are among the most numerous animals on Earth.
    • They are characterized by their cylindrical bodies and unsegmented appearance.
    • Nematodes can be free-living or parasitic, affecting plants, animals, and humans.
    • Examples include Caenorhabditis elegans (a model organism) and various parasitic nematodes like Ascaris and hookworms.
  2. Rotifera (Rotifers):

    • Rotifers are small, aquatic, and often transparent organisms.
    • They are characterized by the presence of a crown of cilia (corona) used for feeding and locomotion.
    • Rotifers are typically filter-feeders and play essential roles in aquatic ecosystems.
  3. Gastrotricha (Gastrotrichs):

    • Gastrotrichs are tiny, marine or freshwater organisms with flattened bodies.
    • They possess cilia on their ventral surface, which they use for locomotion and feeding.
    • Gastrotrichs are primarily detrivores (feeding on detritus) or microphagous filter-feeders.

Ecological Importance:

  • Aschelminthes, particularly nematodes and rotifers, are essential components of ecosystems. Nematodes can affect plant health by parasitizing roots, while rotifers play a role in nutrient cycling in aquatic environments.

Medical and Agricultural Significance:

  • Some nematodes are parasites of humans, livestock, and plants, causing diseases and crop damage. Understanding their biology is essential for managing these issues.


  • Aschelminthes represent a diverse group of pseudocoelomate organisms with simple body structures. They have ecological, medical, and agricultural significance, making them an important topic of study in biology.