Animal Kingdom

Phylum Aschelminthes

Did you know there are some parasites that live in the intestines of human beings? Yes, sometimes humans and animals suffer from such infestation of worms, called ringworms. These ringworms are a prominent species of Phylum Aschelminthes, also known as pseudocoelomates. Let us learn more about them.

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Phylum Aschelminthes

Aschelminths can be free-living or parasitic. The free-living organisms are extremely abundant in soils and sediments and they feed on bacteria. While some others are plant parasites and can cause disease in crops that are economically important. The others are parasites that can be found in animals and human beings.  Some of the parasitic worms include hookworms, pinworms, Guinea worms, and intestinal roundworms.

Ascaris lumbricoides is the Giant Intestinal Roundworm that is an endoparasite living in the human intestine. They are very common in children. These worms cause a disease called ascariasis. Many adult roundworms live inside the intestine, causing obstruction to the intestinal passage. This causes abdominal discomfort, colic-like pain, impaired digestion, diarrhea, and vomiting. Generally, deworming medicines are given to get rid of these roundworms from the body.

Round Worm

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Characteristic features of Phylum Aschelminthes

  • The body of these organisms is unsegmented and triploblastic.
  • They have a pseudocoeloem, where the body cavity is not lined by the mesodermal layer.
  • They are bilaterally symmetric.
  • The body is cylindrical or thread like with elongated, slender worm-like appearance and tapering at both ends.
  • Body wall has epidermis, muscle layer and is covered by cuticle.
  • The body size of these organisms varies from microscopic to several centimetres in length.
  • These organisms are mostly parasitic, with a few free-living
  • They exhibit an organ system level of organization.
  • Externally, there is little differentiation between the anterior and posterior regions. But internal cephalization is present.
  • There is no distinct head. However, the mouth is present in the anterior
  • The digestive system is complete, with a mouth and anus.
  • The mouth in these organisms is terminal and is surrounded by lips bearing sense organ.
  • Amphids and papillae are the main sensory organs.
  • The nervous system consists of a nerve-ring that encircles the oesophagus. From it, nerves extend out anteriorly and posteriorly.
  • Respiratory organs are absent. Respiration occurs through the general body surface. It is aerobic in free-living forms and anaerobic in parasitic organisms.
  • The excretory system has canals and gland-like
  • Sexes are separate and are unisexual, exhibiting sexual dimorphism.
  • Fertilization is internal.
  • They are ovo-viviparous, oviparous or viviparous.
  • The life cycle of these organisms is complicated. It may be with or without an intermediate host.


  • Ascaris lumbricoides – Round Worm
  • Enterobius vermicularis – Pinworm
  • Ancylostoma duodenale – Hookworm
  • Wuchereria bancrofti – Filarial worm
  • Loa loa – Eye Worm

Solved Questions for You

Q: How is the body cavity of an Aschelminth different?

Ans: The body cavity of phylum Aschelminthes is called pseudocoelom. It is filled with pseudocoelomic fluid. The body cavity is not lined by the mesodermal layer.

Q: What causes Ascariasis in humans?

Ans: Ascariasis in humans is caused by roundworms and is scientifically known as Ascaris lumbricoides. It is an endoparasite, living in the intestines of humans, causing intestinal obstruction, abdominal pain, and diarrhoea.

Q: What is the scientific name of pinworm?

Ans: Enterobius vermicularis

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