Flabby whalefish are small, deep-sea cetomimiform fish of the family Cetomimidae. They are among the most deep-living fish known, with some species recorded at depths in excess of 3,500 m (11,500 ft). Juveniles are known as tapetails and were formerly thought to be in a separate family, dubbed Mirapinnidae. Adults exhibit extreme sexual dimorphism, and the adult males were once thought to be exemplars of still another family, Megalomycteridae.