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Flatworms lack a specialized circulatory system, relying on diffusion and a gastrovascular cavity.

The Claim

Members of the phylum Platyhelminthes (flatworms) lack a specialized circulatory system.

Verified by Lenz ·

The Short Version

The evidence strongly supports this statement. Standard biology references consistently describe Platyhelminthes as lacking a dedicated circulatory system, with gases and nutrients moving mainly by diffusion and, in larger forms, through a branched gastrovascular cavity. That cavity assists transport but does not qualify as a specialized circulatory system.

Caveats

  • Do not confuse nutrient distribution by a branched gastrovascular cavity with a true circulatory system.
  • One ambiguous low-authority outline appears contradictory, but clearer higher-quality sources overwhelmingly support the claim.
  • The wording matters: the claim concerns a specialized circulatory system, not whether flatworms move materials internally at all.

The Receipts

  1. Platyhelminthes (flatworms) | INFORMATION

    Animal Diversity Web

  2. Evolutionary Adaptations of Parasitic Flatworms to Different Oxygen Tensions

    PubMed Central (MDPI Biology)

  3. 33.2.2: Phylum Platyhelminthes

    Biology LibreTexts

  4. Phylum Platyhelminthes | Biology for Majors II

    Lumen Learning

  5. Section 2: Types of Circulatory Systems

    EdTech Books (Brigham Young University–Idaho)

  6. Worms: Phyla Platyhelmintes, Nematoda, and Annelida

    University of Hawai‘i at Mānoa

  7. Characteristics of Platyhelminthes

    BYJU'S

  8. Flatworms

    CK-12 Foundation

  9. Chapter 8: Platyhelminthes (lecture outline)

    Weber State University

  10. Circulatory, Secretory and Nervous Systems of Platyhelminthes

    Learnpedia (YouTube transcript via learnpedia.in)

+ 2 more sources — see the full list on Lenz

Filed Under

Platyhelminthes