Molecular-based phylogies place the phylum Platyhelminthes in the Protostomia. How do scientists best explain the morphological differences between flatworms and the other members of the Lophotrochozoa?
A. Modern Platyhelminthes do not have a coelom but did originate from an ancestor that had one.
B. The Platyhelminthes clade separated from other clades before coeloms evolved and consequently Platyhelminthes have never had a coelom.
C. Platyhelminthes evolved from an ancestor without a coelom but developed one during the course of their evolution.
D. Some Platyhelminthes have a coelom but others do not and it is difficult to conclude anything about its evolution within the clade.
E. Platyhelminthes originated from ancestors with a coelom and have retained it to the present time.
Answer: A
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