When considering the wormlike phyla within the protostomes,which feature is most useful in distinguishing groups?

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Feeding structures or mouthparts are a key feature used to distinguish the various wormlike phyla within protostomes, such as Annelida, Nematoda, and Platyhelminthes. The type of body cavity (A) and presence or absence of a hemocoel (B) are less helpful in distinguishing these groups, as these features can vary within each phylum or even within different species in the same phylum. While a hydrostatic skeleton (D) is present in some wormlike phyla, it is not a defining characteristic that can distinguish between them.

When Considering the Wormlike Phyla Within the Protostomes,which Feature Is