Platyhelminthes, Nemathelminthes and Annelida · Zoology

Flatworms are described as 'acoelomate' because:

  1. They lack a digestive tract entirely
  2. They have a cavity lined by endoderm
  3. Parenchyma tissue fills the body wall space
  4. They possess a cavity derived from the blastocoel
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Correct answer: Parenchyma tissue fills the body wall space

Platyhelminthes (flatworms) are acoelomate — they lack a true body cavity. The region between the outer epidermis and inner gut lining is packed with solid mesodermal parenchyma tissue, leaving no open fluid-filled space.

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