Hemichordates have now been placed with the non-chordates due to the absence of

Hemichordates are placed in non-chordates because true notochord is absent in them. Stomochord is a a buccal diverticulum which is present in pre-oral region. This structure (stomochord) was mistaken to be notochord and so Hemichordata was categorised under phylum Chordata in the past.