- An order of marsipobranchs, like the Myxine or hagfish therefore the genus Bdellostoma. They usually have barbels across the lips, one tooth on the palate, and a communication between the nasal aperture plus the neck. See hagfish.
- A primary subdivision of myzonts, embracing forms using the roofing of this mouth perforated because of the single nasal canal.
- hagfishes as distinguished from lampreys