一個語言可能會有和半閉與半開的央元音不同的中央圓唇元音 (a rounded /ə/不過因為沒有已知的語言分辨半閉、中與半開的央元音,因此IPA沒有這個單獨給母音的符號,而代表半閉央圓唇元音的符號/ɵ/經常被用以表示這個元音。如果要表達的更精確,半閉央圓唇元音的符號可能會被與開音符號合用而變成:/ɵ̞/.
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