Phylum Aschelminthes: Aschelminthes are commonly known as roundworms. They are characterized by the presence of a pseudocoelom. It is now an obsolete phylum of invertebrates and the animals grouped under this are now kept in ten different phyla.

• Body in aschelminthes (Nemotoda) is cylindrical [bilaterally symmetrical] rather than flattened.
• They exhibit organ-system level of body organization [there are tissues, but no real organs].
• They are triploblastic. A sort of body cavity or a pseudocoelom, is present.
• They are freeliving, aquatic, terrestrial or parasitic in plants and animals.
• These are very familiar as parasitic worms causing diseases, such as the worms causing elephantiasis (filarial worms) or the worms in the intestines (roundworm or pinworms).
• The body is circular in cross-section, hence, the name roundworms.
• Alimentary canal is complete.
• An excretory tube removes body wastes from the body cavity through the excretory pore.
• Sexes are separate (dioecious), i.e., males and females are distinct.
• Often females are longer than males.
• Fertilisation is internal and development may be direct (the young ones resemble the adult) or indirect.

Classification of Aschelminthes

Aschelminthes is classified into 2 classes i.e., Aphasmidia and Phasmidia.

Aphasmidia

• Phasmids are absent.
• Excretory organs are reduced or absent.
• Examples:- Trichinella, Trichuris, etc.

Phasmidia

•  Phasmids are present.
•  Excretory organs are well developed. 
•  Examples:- Ascaris, Enterobius, Ancylostoma, Wuchereria, etc.

Attempt MCQ on Phylum Aschelminthes

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By Team Learning Mantras