Which of the following animals have a single opening in their digestive system that serves both as a mouth and an anus?

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SSC CGL 2022 Tier-I Official Paper (Held On : 01 Dec 2022 Shift 4)
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  1. Arachnids
  2. Echinoderms
  3. Platyhelminthes
  4. Arthropods

Answer (Detailed Solution Below)

Option 3 : Platyhelminthes
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Detailed Solution

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The correct answer is Platyhelminthes.

Key Points

  • Phylum Platyhelminthes belongs to the kingdom Animalia.
  • The organisms are also known as flatworms.
  • These are acoelomates and they include many free-living and parasitic life forms.
  • They have a single opening in their digestive system that serves both as a mouth and an anus.
  • Platyhelminthes have the following important characteristics:
    • They are triploblastic, acoelomate, and bilaterally symmetrical.
    • They may be free-living or parasites.
    • The body has a soft covering with or without cilia.
    • Their body is dorsoventrally flattened without any segments and appears like a leaf.
    • They are devoid of the anus and circulatory system but have a mouth.
    • They respire by simple diffusion through the body surface.
    • They have an organ level of organization.
    • They do not have a digestive tract.
    • The space between the body wall and organs is filled with connective tissue parenchyma which helps in transporting the food material.
    • They are hermaphrodites, i.e., both male and female organs are present in the same body.
    • They reproduce sexually by fusion of gametes and asexually by regeneration by fission and regeneration. Fertilization is internal.
    • The life cycle is complicated with one or more larval stages.
    • They possess the quality of regeneration.
    • The flame cells help in excretion and osmoregulation.
    • The nervous system comprises the brain and two longitudinal nerve cords arranged in a ladder-like fashion.

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