None of these characteristics are true for all chordates. Chordates are defined by having a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post- tail at some point in their life cycle. Some chordates may have a coelom, mammary glands, or bilateral symmetry, but these are not defining characteristics of the phylum. Additionally, chordates are triploblastic, not diploblastic.
