Why doesn't a flatworm have a circulatory system?

a. The animal is thin enough to permit effective gas exchange by diffusion.
b. There is not enough room for a circulatory system because of the large gastrovascular
cavity.
c. The animal lacks muscles, so it could not have a heart to pump blood.
d. Only bilaterally symmetrical animals need a circulatory system.
e. Only vertebrates have circulatory systems.


A

Biology & Microbiology

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