Use the figure to answer the question.
A: Morphological phylogeny.

B: Molecular phylogeny.

In the traditional phylogeny (A), the phylum Platyhelminthes is depicted as a sister taxon to the rest of the protostome phyla and as having diverged earlier from the lineage that led to the rest of the protostomes. In the molecular phylogeny (B), Platyhelminthes is depicted as a Lophotrochozoan phylum. What probably led to this change?
A) Platyhelminthes ceased to be recognized as true protostomes.
B) The removal of the acoel flatworms (Acoela) from the Platyhelminthes allowed the remaining flatworms to be a monophyletic clade clearly tied to the Lophotrochozoa.
C) All Platyhelminthes must have a well-developed lophophore as their feeding apparatus.
D) Platyhelminthes' close genetic ties to the arthropods became clear as their Hox gene sequences were studied.

Question

Use the figure to answer the question.
A: Morphological phylogeny.

B: Molecular phylogeny.

In the traditional phylogeny (A), the phylum Platyhelminthes is depicted as a sister taxon to the rest of the protostome phyla and as having diverged earlier from the lineage that led to the rest of the protostomes. In the molecular phylogeny (B), Platyhelminthes is depicted as a Lophotrochozoan phylum. What probably led to this change?
A) Platyhelminthes ceased to be recognized as true protostomes. 
B) The removal of the acoel flatworms (Acoela) from the Platyhelminthes allowed the remaining flatworms to be a monophyletic clade clearly tied to the Lophotrochozoa. 
C) All Platyhelminthes must have a well-developed lophophore as their feeding apparatus. 
D) Platyhelminthes' close genetic ties to the arthropods became clear as their Hox gene sequences were studied.

Quizplus · Accepted Answer

The shift in Platyhelminthes' placement from a sister taxon to the rest of the protostomes to being part of the Lophotrochozoa is likely due to the removal of the acoel flatworms from the Platyhelminthes group, which made the remaining flatworms a monophyletic clade that is clearly tied to the Lophotrochozoa in molecular phylogenies.

Use the Figure to Answer the Question