Bio: Symmetry/Evolution

[HannibalLecter]

In which of the following phyla are only bilaterally symmetrical animals found?
(Chordata, Echinodermata, Mollusca, Ctenophora, Platyhelminthes)

The answer states it is Platyhelminthes only but doesn't bilateral symmetry start off after the clades of Cnidarians and Poriferans so technically mollusca, Platyhelminthes, and Chordata all have bilateral symmetry.

Echinodermata I left off because of its radial symmetry

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[mh0000]

The question asks which phyla that ONLY bilateral symmetry is found. I don't know of any radial symmetry in platyhelminthes. Cnidarians do have radially symmetric species though, so they wouldn't be an answer choice. On the top of my head, I can't think of any radial chordates. Maybe tunicates? Mollusks, I can't think of a radial species either... Is the trochophore radially symmetrical? Some mollusks have a trocophore larval stage. So you might be right about chordates and mollusks.

 

[HannibalLecter]

This is just a dumb question, my bad for even asking it. It clearly states all three: Flatworms, Chordates and Molluscs are included in bilaterians

http://en.wikipedia.org/wiki/Bilateria