sˈɪns ðˈɛn, ɪt hˈæzbiːn ɹᵻklˈæsᵻfˌaɪd baɪ mˈɛni wˈɜːkɚz æz hˌævɪŋ mˈɛni dˈɪfɹənt ɐfˈɪnᵻɾiz, sˈʌtʃ ɐz æn "ʌnspˈɛʃəlˌaɪzd ˈænɐspˌɪd", ɔːɹ æz ɐ sˈɪstɚ tˈæksən tə ðə lˈæmpɹiz, ɪts dˈɪfɪkˌʌlti ɪn klˌæsɪfɪkˈeɪʃən dˈuː tə dˈɪfɪkˌʌltiz ɪn ɹˌiːkənstɹˈʌktɪŋ ðɪ ɐnˈæɾəmi; ɪt dʌznˌɑːt pəzˈɛs ˌɛni jˈuːʒuːəl kˈɔːɹdeɪt sɪnˈæpəmˌoːɹfiz.
Since then, it has been reclassified by many workers as having many different affinities, such as an "unspecialized anaspid", or as a sister taxon to the lampreys, its difficulty in classification due to difficulties in reconstructing the anatomy; it does not possess any usual chordate synapomorphies.