Multiple choice

Circulatory system is absent in:

  1. annelids

  2. flatworms

  3. anthropods

  4. cephalopods
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Flatworms (Platyhelminthes) lack a specialized circulatory system because their flat, thin body shape allows sufficient diffusion of gases and nutrients directly from the environment to body cells. Annelids have a closed circulatory system, arthropods have an open circulatory system, and cephalopods (mollusks) have a well-developed closed circulatory system with multiple hearts.

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